Vintage KIM-1: Disaster to Redemption

[@DavesGarage]

Just an update for folks: what Jonathan wound up doing was to bridge the 12V regulators so we only need to pass 5V and 12V now. That allows me to run a simple dual-voltage Meanwell supply, which is now hard-wired with yellow/red/black cables to the power input lugs. So there's no guesswork, and not 4 voltages anymore. The only downside is the PROM burner likely won't work that way for some old EPROMS, which can take a lot of voltage to write. I've got a 2516 eprom burner now for the PC, so I don't really need to write new roms in the KIM, but the PROM board would be a nice place to put a copy of SuperMON or something!

[@iroll]

@@willynebula6193 I was going to suggest Adrian Black; he's in the pacific NW and sometimes has surpluses of certain items (like potentially an 8" shugart drive)

[@KennethScharf]

Years ago (1970's) when I was in college, I worked part time at one of the first computer stores in NYC. It was a one man shop, with me being a programmer and repair guy. The shop sold mostly Imsai and SWTP computers, both in kit form and assembled. I was the guy building the kits to sell as assembled. One day I came in to find the owner in a state of shock. He had been debugging a customers memory card in his own Imsai, with memory card on an extender card plugged into the Imasi. He'd found a suspect chip and was going to remove it. He grabbed for his soldering iron which was stuck into a steel wool pad to clean the tip. The steel wool pad sailed through the air and landed in the motherboard of the computer creating a shower of sparks. Then the computer was dead. He expected to have blown every IC in the thing. I told him, I'd try to fix it, but he was doubtful that I would be able to. So I started probing the bus, with a logic probe (He ad an oscilloscope, but I figured I could do as well with the simple probe at first). I found some signals that didn't map out right, and then went on to the front panel board. Eventually, I traced the missing signal to a SN7400 chip on the front panel. I replaced that IC, and tested the computer. It worked! The ONLY fried part was a 25 cent chip! (How lucky can you get?) That resistor on the CE line is probably a low ohm device. It's purpose is likely to reduce 'ringing' on the signal. The layout of that board probably wasn't perfect, and there was some cross talk between lines. Or maybe due to prop delays or something the signal at the CE lines simply wasn't clean. Adding that resistor could clean that up and make the memory more reliable. Sometimes a very small capacitor to ground will do the same thing. I once had to debug a printer interface on a home brew computer that wouldn't work EXCEPT when I was probing the strobe signal with a scope. Turns out the scope probe added a small amount of capacitance to ground and that quieted down a noisy line. The fix was to put a 10pf cap to ground where I had probed. A series resistor might have done the same thing. 3.5" and 5.25" HD PC drives have the same track layout and clock speeds as an 8" floppy. So unless you have some 8" floppies you need to read you can use the smaller disks with your KIM FD controller. Just make sure you use HD media. Some cable rewiring will be required however.

[@Pistoletjes]

About 8" floppy: I recentely saw in one of CuriousMarc's that he has a stack of 8" drives. Glad that you we're able to restore this gem.

[@OldePhart]

I came here to suggest the same thing. He also showed they weren't bad to repair either..

[@cherrymountains72]

Your videos are always a pleasure to watch Dave, all the way to the end. I much respect your humility and kindness in sharing your faults and what you learned from it. Take care 😊

[@richardmassoth8237]

This is a special video for the old-timers! Don Lancaster's TV-typewriter book (and project) is definitely a "blast from the past" for the early computer hobbyist. The techniques that Don used appear in a variety of early "hobbyist" video terminals and live video for early Osborne, Heathkit and other video (or terminal) systems. My suggestion is to assemble a specific power supply for your collectable beast. My old S-100 bus machine was assembled with a separate power supply for the regulated and unregulated voltages needed by the machine. I built a power connector harness to handle my specific needs with this machine, and it avoids the mistakes that you caused you to let out "the magic smoke". Now, it's "how good are those electrolytic and early tantalum capacitors" and how good is the thermal grease on heat-sinked regulators that can bring forth the incense of dying vintage electronics. I do have an 8 inch floppy drive pair, but they are hard-sectored. You really want an old Shugart 8" floppy drive. I have one, but don't know how well it works, as I've used it mostly as a demonstrator.

[@DavesGarage]

It's now all nicely wired with dedicated color coded lines to the supply itself, so pretty much foolproof at this point! I think I'll add a Deutsch connector to finish it off!

[@oldestnerd]

I still have a TV Typewriter board with a Cherry Keyboard (I think) that I built into a nice case. It hasn't been powered on in over 25 years. I should give it a try...

[@oldestnerd]

Correction: I checked and what I have is a TV Typewriter 2 which was not designed by Don Lancaster.

[@johnjohnson5028]

In Waterloo Ontario, circa 1975, a couple of entrepreneurs started a company manufacturing CRT computer terminals based on Don Lancaster's information. Volker Craig terminals were sold to local schools and universities to hook up to their IBM or DEC mainframe computers.

[@matwyder4187]

It would be really nice if Mr. Chamberlain was interested in talking about his memories, maybe having him for an interview? These people were true pioneers and inventors with rock solid determination, it's quite hard to imagine how they managed to make steady progress in an era where all of this early tech was still highly obscure and likely prohibitively expensive, leaving no much room for mistakes.

[@DavesGarage]

For the curious, the flag pops up during an accent slip, when I say "fill-um" for "film" :-). And I'm pretty sure I mean inverse when I say converse!

[@whollymindless]

Decades of SCTV, The Frantics and Red Green make me fluent in Canadian, eh? (although I struggle with Canadian punctuation.)

[@SeanBZA]

I had an avionics computer come in with an odd issue, power on self test completed within a hundreth of a second, not the regular 2 seconds. Tested, and, while it was running fine, and all the internal checks showed it was functional, and it was completing it's tasks correctly, it was just behaving "odd". Opened the case (84 M4x12 capscrews, I had bought a cordless screwdriver long before, and worn out the original gearbox, it was on the upgraded Black and Decker powder metal gears for later models) and went through the power supply, measuring voltages. -21V ok, -19V ok, -15V ok, -12V ok, 12V ok, 15V ok. then the last rail, 5V, meter did a range adjust, which it should not have to do on the 10V range, on that Racal Dana meter. 5V rail was showing 16V, the unregulated input bus voltage. Power off, and start with the power supply, replacing every part in that 5V rail, including the resistors on the board, and also the over voltage crowbar circuit, that should have blown the 10A fuse on the transformer rectifier board next door to it. All new parts, from zener diodes, power transistors, resistors, capacitors, driver transistors, the failed SCR, and the diodes that fed power to the system self test for power system, on the next board. then power on, still have that self test execute too fast. Pull out all cards, and replace with spares, then test again, perfect, so a card fault. Then start replacing card by card, till I get to a card that, amongst other things, contains the system memory, IC's that are even rarer than KIM1 rom, a MK3007 serial memory pair. Also has the self test circuitry in it, and looking at the card I can see one of the surface mounted devices looks darker. Put a spare card in there, the rest of the original cards back, and power on, self test executes perfectly. Run diagnostics, check all the analogue side inputs and outputs, and put all 84 capscrews back in, and box it and send it back out. Kind of needed, I had 11 behind me in a rack awaiting repairs, held up by needing million dollar power supplies. Never got to them before leaving, and anyway the lot went into a destruction session 2 years later on, as the airframes were demilled for the new owners. Looked at the card, and the only part, of the hundreds of exotic, unobtanium, and covered by some secret acts, parts in there (the stored program, in Intel Hex, on punched tape, that did all the calculation and a lot of logic decodes, using a board of 1k EPROMS) that did fail from having however many hours of 16V applied, was a single quad open collector (ironically rated for 30V on that open collector) gate, where only 2 of the gates were used, along with a resistor, to combine all the logic to drive the 12V relay, that drove that self test light.

[@technocity6720]

I dont see my other account post idk whats up with that Ill just repost to make sure you see this. When a chip fails it produces heat usually you could load test it "lewis rossman load test imac's with christmas tree lights in line". Some random chip took the blunt of the damage instead of the kim-1. If you look at the schematics of the IC's it wouldn't be a surprise to see some diodes and or a transistor in there. (A transistor is basicly two diodes put to geather). One of the original engineers at commodore can be found through the St. Louis & Suburban Radio Club. I know b/c he gave me a vic20 im also a ham radio operator and some of those guys are the best in electronics. When the guy gave me the VIC-20 he told me commodore had a bunch of extra parts from a arcade project that failed they told him to make a computer out of this pile of overstock parts and the VIC-20 was born. What I have is one of the first original production units. I also have some rare prototype games and memory expansions that were included with the vic. On the radio side of things this guy set up a bunch of radio repeaters in the STL area on the 2m ham bands that use a vic-20 instead of the modern day vertex. They still work to this day. To becan out a call sign every hour as required by the FCC. Hes a big radio guy I dont wanna name drop but it shouldnt be to hard to track the guy down. If you send a e-mail to the (SLSRC) guys i'm sure they would be glad to help you out.

[@r2db]

The gods of vintage electronics seem to often require a sacrificial offering of magical blue smoke as a relatively common requirement for their blessing to continue the electronic necromancy.

[@michaelmiller3012]

So, effectively what we have here is what I like to call a "teachable moment" when it happens to me. A disaster situation that through troubleshooting and resolution drastically improves your understanding and knowledge (and thus enjoyment) of your newly repaired device.

[@ch2laughlin]

It is deeply satisfying to see these old hardware friends once again as you work on them. Thank you Dave.

[@1asdfasdfasdf]

Good olé C64. That's where I learned my Pokes & Peeks. Those were the days ;-)

[@paulscarlett4346]

Recently, after making a something work from first principles, I am reminded of the scene in Castaway where Tom Hank's character celebrates "I have made fire". So getting to the point where you have a working character set on your Kim 1, I would consider a "I have made fire" moment -- sorta the opposite of letting out the magic smoke. Congrates! Truly enjoy the videos.

[@TrimeshSZ]

I would guess those resistors are series terminations to try and match the board impedance and hence reduce overshoot on signal edges. They were especially important on those older RAM chips that used high level signaling because a 12V signal with ringing could overshoot past the absolute maximum rating for the pin and ran a risk of damaging the chips.

[@garyflies]

Hey Dave, As an electronic repair tech myself, your fault finding path was very good. Its all about finding and repairing faults with minimal effort. If I have a second working device, the first thing I will do before even diving into schematics is to take comparison measurements in areas of the circuit that seem likely to have the fault and work backwards from there. Exactly the same as your method. Well done repairing the fault.

[@Choppy_PHC]

in regrads to the Chip Enable pin, youre correct they will have an internal resistor that either pulls the signal high or low depending on the chip design. if you look at the pinouts for the RAM chips you can see if a signal is active low as it will have a bar (line) above the "CE'. the reason for having an internal pullup/pulldown resistor is generally so you dont get floating I/O causing erratic behavior.

[@jasoneyes01]

This channel brings back so many memories, thank you so much Dave for everything you show and teach us. Coding Windows device drivers struck my curiosity recently. Any content you do is awesome.

[@joeteejoetee]

When one adds 47 Ohm resistors to a digital output it is usually to reduce "ringing" and ground bounce. The output impedance of a TTL line buffer/driver is very low and when it enters a long trace with a normal 50-ish Ohm impedance it may not propagate as a clean square wave all along the trace. It may over-shoot on the rising edge, and undershoot and ground bounce on the trailing edge. The Amiga Zorro bus (7Mhz) motherboards have similar resistors at the signal entry-point of the bus traces, and also 2 resistors at every end of those traces: 1 R pulling high, and the other R pulling to ground forming a bus termination. (Joe Torre - Former Gateway-Amiga Hardware Engineer, and BoXeR engineer.)

[@joeteejoetee]

When the trace length is short (0.1" to 2.5") and it only connects from point A to point B (or maybe C) it will not _require_ the impedance resistor, and will propagate as a clean square wave. However Resistors are often included to reduce RF noise, and also to allows easier PCB trace routing under and between the physical space below them --> especially on 2 layer PCBs.

[@robertleemeyer]

Wow! This was a lot of fun to watch! There is no better experience than "raising the dead" after smoking some components - and getting to know some awesome people along the way as you troubleshoot the hardware (and/or software) that they designed back in the day! Thanks for bringing it all together in this wonderful presentation! And sorry for the excessive exclamation marks -- but this project is very exciting for me since I was once a teenager daydreaming about the KIM-1 back in the day!

[@henryyoung7184]

Loving this because I remember drooling over magazine articles about the KIM-1, probably about the age I should have been drooling over a different genre of magazine. I was never able to get a KIM-1 but we had a PET at school and I went on to design and build something similar to a KIM-1 based around a 6809, all wire wrapped on Veroboard. Happy days. Girls came later ... fellow ASD'er too :)

[@estcyr10]

This is great! I bought my KIM-1 in April, 1976, and it still works fine: who needs that pesky ROR op code! I still have the manuals. Early on, I added a 4k memory board, which is now defective. My KIM-1 is mounted in a briefcase, along with breadboard sockets and several other power supplies. Thanks for this!

[@SeanBZA]

The RAM chips have a weak NMOS transistor in them, which is tied to 12V, to act as a pull up, and to also supply a low current, as it is a very small channel device, so it has a high resistance. Smaller than using a polysilicon resistor, and as a bonus when at 12V it also acts as a clamp diode to prevent overshoot. The 470R resistor is there to damp down the transmission line of all the chips together in a long row, dissipating the spikes that would otherwise drive the chip inputs into clamping to the power rail, and thus also having a chance of turning on the parasitic PNPN thyristor inherent in almost every IC. Made by the junctions used to isolate parts, and, while the transistors made in that way are very poor, they do normally have a gain a tad over 1, so the 2 PNP and NPN structures can act like a thyristor, as they will latch themselves on, shoring out the power rails, if you exceed the allowed input current, typically 100mA, but in the data sheet you will see in absolute maximum 50mA, as pretty much all will not latch up at 50mA unwanted input current into the internal protection diodes that are part of these transistors. The resistor, along with the capacitance, damps down the rise of the enable pulse, and you still see this on your DDR memory, as resistors, typically 10-33R, in tiny arrays on the address and data lines to the DDR sockets, normally 4 resistors in a tiny package, that perform this function, though a lot of the DDR chips themselves also incorporate the resistors into the die itself as well, as that improves the speed at which it can operate. Done on all the address, control and data lines, turning them all into transmission lines, so all have to be the same length, so as to not skew the data applied, as 10mm extra trace on one line will mean you lose 100MHz, or more, in maximum clock rate you can use, as the chip will start to get errors, as the data or address does not arrive in step on all pins.

[@javabeanz8549]

Thanks for that explanation, as it really gives meaning to "use matching RAM." With the RAM speeds today, even small differences could cause errors.

[@MarkSeve]

Thank you for sharing Dave, and for being frank.

[@thisisreallyme3130]

Hey Dave awesome series. Please consider creating a Playlist for the KIM-1, and maybe another Playlist for all the CC65 stuff. Keep these coming these low-level series are my favorites.

[@jameswilson1972]

Wow, that was quite an odyssey of repair and was definitely entertaining. It's so cool that you were able to find the Chamberlain guy. I was amazed by that. Thanks for yet another great video, Dave.

[@voidstar1337]

Recall how Woz's Apple-1 was $666, in 1976? (of which only about 180 were made and sold - thus starting the Apple tradition of overpricing from the very beginning :) ). In that same year, the KIM-1 was about 1/3rd that price (around $200) and was advertised for several years (see old BYTE magazine issues, on up to early 1980s). In an interview a few years back, I recall Chuck Peddle saying for sure over 10,000 KIM-1 boards were sold (but probably not over 20K) - mainly used in industrial machines (but no definitive examples to cite). The "1" in KIM-1 was for 1K (memory), amazing story how Peter Jenning (also from Canada, not the news person) fit his microchess in that 1K. This is a great find and appreciate your dedication to the fixes (I fried a power supply on an IBM 5110 once, so can totally relate to the frustration). Very nice to really see how the KIM-1 was a core component to what could become a more functional system (the little number pad and LED wasn't intended to be the full extent, but were just demo/test aspects). I've read that before the KIM-1 there was a TIM-1 in '75, but I don't know too much about the TIM (I'd guess the TIM was basically prototype boards leading to the KIM, I'm not sure if the TIM was ever commercially released).

[@estcyr10]

I purchased my KIM-1 in April, 1976, for $245. There was an ad in Byte magazine. Still works fine, but the 4k memory board I added later is not working right.

[@TimePilot2084]

I like to watch these videos as I sit in my own "garage," staring blankly at ancient and mysterious circuit boards I've removed in an attempt to repair them. It is comforting to know that even geniuses such as Mr. Plummer occasionally spend their time doing the same thing.

[@Enjoymentboy]

I've done very similar to this but I'll one-up you. in my case i put 12v into 5v with a positive center power jack and a negative center power plug. Very little magic smoke but a helluva bang. No repair attempt needed in this case as was evidenced by the hole in the board afterwards.

[@jonatdrmarlo]

This brought back a lot of happy memories. First job out of two year tech school in the mid 80's, engineer asks if I'd like to help design and schematic entry of a dual 80186 display system. ...want to wire wrap it? ... debug it? ...do you want to learn how to write embedded software? I ended up as a PCB designer, thanks for the happy 'where it all started' memories.

[@ambrovanwyk6522]

You are correct about the internal pull-up resistors on an input (CE) line. The resistor/capacitor network might be a circuit to generate a shorter pulse (either leading or trailing edge) of the invoming pulse. Is the duty cycle a lot less on the output side? The reason for 2 transistors is probably because every time you buffer/amplify a signal with a transistor, the signal inverts, the second one is to invert it back tonits original.

[@stevenwilson1690]

Actually - no he isn't. The issue is that DRAMs don't like undershoot/overshoot. So by putting the resistor there - you are limiting the rise time of the CE signal. If you look at OTHER DRAM boards - you will often find that all of the address lines & ras/cas lines ALSO have serial resistors - also referred to as swamping resistors present for that reason. They are chosen to create a "critically damped" switching signal. This reduces the RFI as well as removed over/under shoot. Hope that clarifies things.

[@richardbedell6854]

I am just now seeing your video on the KIM-1. I skimmed through maybe half of the 235 comments but did not see a suggestion to how the 16 volts did not fry the KIM powered by a regulated +5V supply. I offer a suggestion: The +5V is a regulated supply, and depending on the manufacturer, it may have output over-voltage and reverse voltage protection circuits. Some even had a circuit called a crowbar circuit that used an SCR. The crowbar circuit is serious about preventing over-voltage; in that when the output voltage exceeded a certain value, the SCR would fire and short the output and keep it shorted until the supply was turned off. An SCR will not turn off until there is zero current flowing through it, so the supply had to be turned off. The name crowbar is from the analogy of throwing a crowbar across the power bus in an emergency to shut the power bus down. Back in the day, large capacitors were used for filtering high current supplies. Enough energy came out of the caps that a simple screw drive would blow like a fuse rather than clamp the output. Hence, the crowbar. Looking at the User manual for the KIM, it shows a suggested power supply. It uses an LM309 regulator in a TO-3 package. To verify my mental RAM, I looked up the datasheet and it has an internal 6.3V zener diode to clamp over-voltage. So how did the protection circuits in the 5V regulated supply save the KIM? Well, the 16V came in backwards and triggered the protection circuits. But shouldn't the 5V supply had prevented the output from rising too high? No, the power supply is design to push current not sink it. So when the voltage when above the regulation voltage the output of the 5V simply turn off. But the protection circuits saw too high a voltage and clamped it. Of course, all that is theory unless I know what manufacturer and model supply was used to determine if there was and what kind of output protection it has. There are other possibilities such as the KIM-1 having onboard voltage protection but the schematics I found showed no such protection. It would also be interesting to know what the supply rating are/were for the Reg 5V and 16V supplied. I suspect the 5V was on the order of a one or more amps and the 16V was lower if not much lower. The current drawn from the 16V supply must be low or the wiring and PCB traces were hefty since you did not mention anything about blowing traces off the boards or melted wires. As for the CS (Chip Select), being high on the RAM, I would need to try to find some datasheets at work for the 6102 RAM. I assume that is the RAM used on the RAM board.

[@MisterItchy]

This was very interesting! Yes ... when you have suspect signals that you are not behaving as expected, isolate the components so that you know what you are testing and nothing else interferes.

[@anon_y_mousse]

I watch Adrian too, he's definitely one of the best old tech guys out there. Feels like every old tech channel I watch, watches each other.

[@stevedonkers9087]

The Usagi Electric channel may have the 8 inch Shugart drive you're looking for. He does a lot of great videos with vintage mini-computers.

[@CallousCoder]

Awesome ❤Thanks to people like Johnathan and Dave this great system is alive and working.

[@zh84]

"I don't have an 8 inch floppy drive..." Curious Marc has a whole batch of them that he's working through and getting back into working order.

[@davidhingst7063]

Wow Dave this is a blast from the past for me. I still have my KIM-1 purchased in the 70's for $279 which was my first real computer. I literally just pulled it out this weekend thinking about getting it going again. It hasn't been powered up since 1980. That computer taught me a lot and I used it extensively during college learning microprocessor basics. I also went through the line of the original PET with the chicklet keyboard and the CBM and had a VIC-20 and C-64. Those were fun machines to program. But the KIM-1 is my baby. Oh and somewhere I have a 4K RAM board I put together back in the day. The board was like $25 but RAM was about $100 per K at the time. I remember struggling to come up with the $400 to populate the board. Imagine paying that kind of money for the 16 gigs I have in my laptop today! Thanks for the video. It took me back to a time I did a lot of the same kind of work. I don't get to break out the soldering iron much these days but I sure enjoy it.

[@frankbezemer8405]

Hey Dave, really enjoyed the story! Especially the Chamberlain bit 🙂 You were lucky he was still alive and of healthy mind!

[@jmzorko]

This brings back memories. I started in 1980 on an RCA COSMAC VIP, since I couldn't afford anything else as a highschool student. Though it had a language called CHIP-8, it was horribly slow, and the only way to get decent speed out of the hardware was to code everything in 1802 machine code. So, that's what I learned. I still have the VIP around here, but it's in bad shape and hasn't run in years.

[@anon_y_mousse]

Maybe give fixing it a shot. You might find that you still enjoy it, or possibly enjoy it more.

[@retroriff]

Your board was protected because the regulator chip or pass transistor blew open circuit , install 7800 series or 7900 series for negative voltages as an upgrade. Keep up the fine work ! Oh btw, regulated voltage sections mostly always go open circuit when in fault mode

[@DadofScience]

This is awesome work, Dave. The effort you're able to put into these projects is hugely appreciated and the respect I have for the folks who built these machines back in the day. I've been playing with building subsystems of basic computers, such as transistor based binary adders, clocks and memory blocks, and being all new to me it's a long slow road of self-education and trial, error and troubleshooting. Very rewarding, but also very frustrating at times. The questions you pose to the audience are also great and I hope you are rewarded with the audience interaction and answers you so well deserve. Many thanks from Australia.

[@networkg]

Dave, thank you for your book, it has taught me to look at autism as a difference and not as an automatic disability. Thank you as well for these videos, they are both entertaining and informative. I hope you continue to get as much enjoyment making them as I do watching.

[@yaidontknowwhattoput]

A great combination of effort and knowing when to ask for help.

[@Benfoxmra95]

great video. the story of connecting with the original designer is half of the fun of projects such as this, sometimes even more than half. Those types of encounters add something to the experience that's a bit indescribable, sort of like mile markers on a highway that are memorable for whatever reason. I've been watching your videos for awhile now and one thing that I am curious about is if you use some type of teleprompter or cue cards? if not, your ability to speak fluidly and stay on topic while recalling either information or experiences is exceptional. This is a indicator that you fully understand the topics you are speaking on. a rare trait. I've tried to make some videos and I find myself stumbling and saying "ahhh" a lot. a bad habit I've had since childhood I've never been able to break.. anyways, please keep making the videos, they are appreciated!

[@ronnylucas8857]

The air gap in the resistors fracture acted as a dielectric, so it behaved as a capacitor, with some resistence in series it became an filter... (maybe)!

[@MarianoLu]

I was waiting for the KIM updates Dave! Looking forward to see what happened.

[@walterpark8824]

Very satisfying episode! I would have hate d to go through so much, get so much right and still fail to revive.. Glad to know that Hal Chamberlain is still alive. In the days when I started putting hardware together, his logic was a major teacher.

[@rafaelgcpp]

Been there, done that. I was powering a home built DAC, back in 1990, the ones we used on the parallel port for MOD players. Long story short, I connected 8V unregulated instead of DC to the DAC. When I figured out the magic smoke was leaking from my dear DAC0801, I yanked the wire but then it slipped and touched the 127V side of the power supply I built for it. Then I lost a brand new 486DX mother board, IDE controller, multi I/O port. Thankfully the 486DX33 survived, as well as my spanking new Hayes modem! The HD and floppy drive survived, but the HD needed to be formatted

[@johnjohnson5028]

Re: CE. Pulled high. As I recall, TTL and CMOS inputs are designed to pull high with a high Z impedance. But through the semiconductor gate design - not a resistor per se. And yes, this is deliberate for the reasons you stated. The high Z allows the driving circuit to pull low. Signed. JohnJ 70 yo Canadian in Ontario.

[@agrofindastation]

Many years back, I went bar hopping with a buddy who kept shoving jagerbombs my way. The next morning, my heart was still racing and then I looked up and realized that it was redbull and Jager, and was at least happy to realize I wasn't going to die for some unexplainable reason....but possibly because of a known reason.

[@billsherman6129]

Oh what fun! Superb stories! I got my first 7400 (not LS but the full power unit) from a repairman who was working to repair some computers at the Boston Museum of Science while I was still a pre-teen. I ended up going into software, but I still have fond memories of soldering and assembling a Heath H-89 computer with my parents, who had both been hams. 🙂 I've still got 'em (the computers, alas, and not my parents). I should power 'em up (the computers) to see if they still work. HDOS!

[@choppergirl]

Can't believe I actually dated someone that did wire wrapping experiments on a Kim-1 for their lab in college. They showed me their finished project. As a Commodore amateur programmer, I was like wow! Low level stuff! You smoked me with my assembly hacking, you're doing stuff on the bare metal. I had a job at the time coding in the storage room on a PET, until I found a PC AT at 12mghz in an abandoned lab that could compile basic, and do it at the speed of light. Dang, I've never seen a PET that retrobrited. Were they ever really that color? I need to go take a look at mine. I don't think it's anywhere near that color. I destroyed my first quadcopter by plugging the XT60 power connector in backwards on the bench. Kapow! They are designed not to mate to protect you from reversed polarity connections, but surprise, the manufacturer of my quadcopter had bought some out of spec XT60 connector that defeated that protection by making the prongs just a little too long. All you can say after that is "Are you shlttlng me!!!! Are you shlttlng me!" and swear and curse lol

[@Lantertronics]

16:15 Hal Chamberlin, author of Musical Applications of Microprocessors. I've spent countless hours poring over that book!

[@chemtype]

Probing DIP chips with a scope probe can be an easy way to fry chips. You gotta be careful not to bridge the pins accidently, I've certainly done that a few times.

[@DavesGarage]

That's why I moved so slow, but you're right of course!

[@byronwatkins2565]

TTL inputs float high unless something (e.g. an output) sinks ~100 uA of current to indicate a low. But, it should be 5V instead of 12 V. The broken resistor prevents anything from pulling this input low.

[@cowasakiElectronics]

A 1.2Mb 5.25” floppy should be compatible according to Adrian. Might be useful just to get it up and running.

[@a4d9]

The electrical interface has signals on different pins.

[@safetyharborfirearms]

I stumbled on to your channel by accident - Early eighties I worked for a small company building lab test equipment. Listening to you rattle off the chip types and such reminded me of those days ....they still had a Intel 8 inch floppy drive...20 meg platter hard drive was a big deal.

[@souta95]

If I had been born about 20 years earlier, I probably would have ended up in a career path similar to you. (I currently work in tech support.) I'm not software developer, but I find this hardware stuff fascinating. I am currently working on fixing up an old Kenwood ham radio transceiver from the early 80's.

[@TimePilot2084]

My life parallels yours, @souta95. Except perhaps I only need to have been born 10 (or even just 5 years) earlier. LOL.

[@julianbrown1331]

RE: the mystery CE signal; putting a pull-up resistor on a heavily used logic line can be used to overcome fan-out. If you have a weak driver to the CE signal it might have been done to give the driving chip a boost. If the trace was cut but the pull-up is still active you would end up with a permanently high signal. Obviously just guessing... no substitute for proper diagnosis

[@kooziesan]

Such a great video. I love seeing this relic rise again

[@RussellBaker]

Taking me back, I started on CESIL on coding sheets to run on the College mainframe with a tiny bit of BASIC in High School, then later on Assembly on the KIM -1 in College

[@dr.strangelove5622]

05:30, regarding the question on why KIM - 1 didn't get destroyed by high voltage, I believe you will need to take a closer look at the end of the chip's datasheet where V-t curves and numerous other curves are present. It has been over 2.5 years since I last did an electronics project, but I do remember connecting the Vcc of ATmega8A microcontroller to 12V instead of 5V while wondering on why it wasn't working correctly. And of course it became super hot!! I quickly removed the 12V supply and I thought that was it for the controller, but after about 15 minutes, when it had cooled down, I connected it to the programmer (USBasp, if I correctly remember its name) and it flashed the program successfully and the controller started working successfully again. I do remember reading about the maximum peak voltage it can survive and the duration for which it can survive, but I don't remember any more details. To cut my ramblings short: your answer lies in the charts present at the end of the datasheet. Usually these chips are sturdy and can survive high voltages for very small duration of time.

[@uploadJ]

All I recall seeing on these data sheets is the ABSOLUTE MAXIMUM ratings (or a narrow voltage range), esp bipolar TTL parts ... MOS and CMOS can be different animals ...

[@NullStaticVoid]

OMG Moiré patterns! That was one of the things I really got into back in my Atari 800 days. In the high res mono modes you could kind of hack the video output to get white plus blue and orange. Something to do with phase I think? It's been 40 years so I'm a bit foggy. Felt like a god when I got overlapping orange and blue Moiré that made a 3rd white one in the middle. Few months after that I made a rotating wireframe cube in orange white and blue. You are so fortunate to have an electronics store like that in your area. They are getting more and more rare.

[@anon_y_mousse]

Tell me about it. I don't even know where a brick and mortar store is to buy components in person. Everything is online these days.

[@MarshallGates]

Curious Marc has a stash of8"drives he is repairing on his channel.

[@Toymortal]

Was just going to say the same thing!

[@markhindsbo7876]

Great video. Thanks for sharing your journey. Just got my own KIM-1 board up and running. Had a shorted capacitor in the TTY circuit and it took me forever to figure out that Basic wouldn't run because the digital flag was set. A simple CLD and all works 😅

[@Rorschach1024]

A 5-1/4" drive uses the same signals as an 8" drive. It just throws away a bunch of ground lines. Adrian Black did a video on this a year or so ago, and may have a working 8" drive you can beg/borrow/steal.

[@DavesGarage]

I reached out to him on it, thanks! If the 5.25" adapter I have on hand is truly compatible, ie: appears just like an 8" to the computer, then I can likely get away with picking up a 5.25 drive somewhere. Pretty sure that the guy I bought the stack from sold the drives separately, and the software to the system went with them!

[@johnsimon8457]

12:26 - Shoutouts to Vetco! I swear the only way a maker-focused / hardware prototyping place like Vetco could exist is in a very tech focused area like Redmond/Kirkland/Bellevue with lots of Dave Plummers around. Like, I'm sure Silicon Valley has one too, I'm not sure where else outside of Shenzhen. What's more is that it's clearly a converted house and has a cat like an old bookstore has cats. Even the more hardcore sections of Fry's or 80's RadioShack (rip) only hold a candle to Vetco. You haven't lived until you've held a capacitor the size of a RedBull can. Y'know this stops feeling like an old computer after a certain point, it's now like a Heathkit on steroids; at it's core it's just several medium sized electronics projects like a calculator or clock radio.

[@InssiAjaton]

I have subscribed this link, but somehow missed it a month ago, then was away a few ore weeks. So, I checked the previous replies and saw some offers of 8 inch floppies already. Consequently, I only tell what I have. My possessions add to one Siemens full height in original Styrox container and needing an AC source for spinning the motor. I also have an old development station with a separate case of dual 8 inch floppies of unchecked brand. Finally I have an IEEE-488 box that has a 5 MB (yes, 5 megabytes only!) hard disk plus a half height 8" floppy. I had it with my HP-87 computer and I had partitioned the hard disk to 4 sections of 1.2 MB, to match the floppy sizes for backup. If I recall, either the hard disk, or the IEEE-488 interface failed and that is how it remains. All this just FYI.

[@plasmar1]

** thinking out loud...... this topic would be an awesome Wozniak collaboration

[@five-toedslothbear4051]

Thanks for a great video! I really love videos about historical computer equipment. I really got my start program in the late 70s on a Wang VS 2200 in my high school, and then some Apple II equipment. What I like about the old computers is that you can actually understand what’s going on, especially with some of the data that has come out about the internals of the 6502. I really like the idea that you can know everything that’s happening from the NAND gates to the screen.

[@simonstroud2555]

Regarding the series resistor added to that signal. I think it's more likely to be a very roughly chosen series termination resistor, which will quell much of the nastiness/reflections of fast edges and also slightly adjust (delay) that signal's timing relative to others, which might be just enough to fix a slightly dodgy timing issue if the KIM-1 design was a bit marginal/gnarly.

[@PretzelPup]

"Don Lancaster" ... wow. I recall reading his columns and articles in Radio Electronics in the 70's and 80's, and in other such mags. Those two words triggered so many memories.

[@williamgraham2468]

I took a course in 1991/92 that used the MTU 140 for its lab assignments. I had a couple of 8" floppies with CODOS, but sadly my mother discarded them in 2000. I also own copies of Don Lancaster's Cheap Video Cookbook and Son of Cheap Video. Although I didn't have a KIM-1, I was going to use the idea of CPU-driven video generation in an 8085-based system. I also recall Hal Chamberlin's columns in BYTE, the small systems journal.

[@KitsuneAlex]

I've seen resistors literally break from overcurrent. The heat weakens the core material enough sometimes.

[@oliverw.douglas285]

That was very educational & interesting. I too started my early coding on the Commodore PET. In college I worked with Assembly Code via MASM, & eventually C++. My career took me in a different direction, working with hardware integration in the Telecommunication's Industry. I enjoy your videos & your content. Keep up the good work. :)

[@MonochromeWench]

HD 5.25 inch drives are largely compatible with 8 in drives through the use of a passive adapter and are much more readily available so unless you have original 8 in disks you want to read its probably better to investigate using a 5.25 inch drive instead

[@wrongmouse1658]

Don't feel bad, I once plugged a ‘S-100’ Card into the vertical card slot to a Processor Technology Sol-20 backwards! It cratered twenty chips on the mother board that took me a bit to replace the chips. Will not talk about the 16k memory board that I was testing. The Sales technician at the Bellevue Byte Shop (1977).

[@muddyexport5639]

And I, also, look forward to the next time. Good job.

[@josedias5514]

You Sir, are your worse enemy. I'm glad you got this working again and I hope to see another wounderful tale from the KIM-1 chasis! Stay curious my friend.

[@andycristea]

Great story and outcome. Don't worry about releasing the magic smoke, I once managed to plug a DDR DIMM backwards while having years of h/w experience and it wasn't even my computer!

[@MrMaxeemum]

I'm impressed you managed to fake it in a hardware job using tools you knew such as comparison diagnostics. You may not have had the know-how but you made up for it with confidence, distraction, and bending of the truth. To be honest I made it in my profession in a similar way also.

[@arminth]

I can imagine that the moment you released the magic smoke, a lot of adult language appeared! 😜 Great, it's all fixed and the system is preserved for the future!

[@richardbrobeck2384]

Nice Video Dave and I really find Adrian's channel a great source I miss the days of these early computers Writing software in basic !

[@glitchwrks]

Glad to see the Visable Memory back up and running for you, it was indeed a little bit of a job to fix up! If you end up with an 8" drive that needs serviced, we do that too. Even those awful MITS/Pertec drives.

[@gettnbetter7274]

This is super interesting. One of my first computers was a kim1. I had no idea that microcomputer ever progressed to graphics, I was always limited to that keypad and maybe a thermal printer way back then. I also saw Curious Marc's recent video where he repaired a bulk stack of 8" drives. Your kim1 is wild

[@Karreth]

Old BJT based logic chips usually has an effective pull up resistor on all inputs, so the enable signal of the RAM being high when disconnected makes sense.

[@paulstubbs7678]

Yikes, get rid of all those barrel jacks. In my 'shop' I try my best to limit them to 12V, for external power bricks. A nice multi-pin plug and socket to an all in one box supply, with one power switch is probably the best way to go.

[@Graeme_Lastname]

You brought back a lot of memories. Not make and model but faults and their causes. Keep well m8. 🙂

[@jozsefizsak]

That's rather inspiring. Thank you!

[@chironbramberger]

You could use a HD 1.2MB 5.25-inch floppy drive for development and testing, and then once you get an 8-inch, switch over to that. The two format are supposed to be identical in enough ways that this should be possible. Since 5.25-inch 1.2MB drives should be much easier to get, you can setup and do whatever you need to, and if you blow a drive or anything, it'll be easier and cheaper to fix. Then for the final setup, use the 8-inch drive. Adrian's Digital Basement and CuriousMarc both have done a number of videos about how you can get an older PC that supports 5.25-inch 1.2MB drives to work with an 8-inch drive and the computer has no idea about any of it (for the most part I believe). Anyway, just an idea.

[@PeranMe]

Dude. We need a video where you visit the Vetco place. I need to see that capacitor aisle!! Great video as always, thanks for sharing!

[@williefleete]

I heard somewhere you could use a 5.25" drive in place of an 8" they pretty much have the same signals just needs a 50 pin to 34pin edge connector adapter

[@scurvofpcp]

That board may have been saved from overvoltage by oxidation on the connectors and contact traces.

[@Gryfang451]

Dave, thanks for refreshing the memories for me! I used to repair C64s and Ataris at an electronics shop. Sometimes even the odd Apple II would come in. Good times!

[@blenderbuch]

Great!I learned many things which could help me in the future.thanks for telling.

[@fredkilner2299]

With Zener diodes or regular diodes you can make simple circuits across power rails so over voltage causes high current ~= short threw diodes pulling voltage down and hopefully blowing fuse or circuit breaker before diodes get hot and die. Reverse bias diode across power rails protects against connecting reverse polarity. I'm more paranoid than smart so I have a habit of first connecting things through small resistors so if I short something I don't brake anything.

[@newmonengineering]

The reason one board was not effected by the high voltage boils down to the path of least resistance. It's a voltage divider. On one side probably a direct short or close to it from frying the chip, on the other a longer trace and a higher resistance. Voltage always takes the path of least resistance. Watch the video of the electric maze by alphapheonix for better understanding.

[@the-flatulator]

I learnt very early in my IT career (over 30 years ago)... "never let the smoke out, it's hard to put it back in"

[@PaleozoicPCs]

Re: the mysterious "high" state @9:30 -ish, it's normal for the inputs (like CE) of MOS chips to float high if they're left disconnected, which would be the state with that fractured resistor. (Google "MOS input float high" and the first hit is a TI document titled "Implications of slow or floating CMOS inputs".) Obviously CE isn't an input you'd normally leaving hanging, but as a rule it's bad practice to leave any input on these chips floating because the voltage buildup that produces this effect doesn't reliably *hold* them high, and transients can over time actually damage the chip. (The inputs like to be *solidly* on or off, they shouldn't be allowed to sit in intermediate states.) This is why you usually see external pull-up or pull-down resistors (either is valid) on schematics to tie up all the hanging chads.

[@Richard25000]

I'd say you're right a lot of active low signals have internal pull ups

[@scottbaeder37]

Ahh...The MAGIC SMOKE....not something we like to see....Good explaination of the issue and your approach. Being of the same "vintage" as you are, I can totally relate