Still Broken… but, Different Broken!

[@psergiu]

Take an ASCII chart and mark the characters that are showing up when receiving serial data. ASCII BINGO. From what i see, all the ones displayed are from the first 64 ... numbers, signs and control characters, some of which are moving the cursor on the screen. I have a hunch bits 6 & 7 from the serial port are not decoded to the end.

[@Mike-zl4zs]

I noticed that too!

[@zrodger2296]

I tried (quickly) to see patterns in the characters, but missed this. Well done!

[@Dsschuh]

I was wondering if the characters and the positions matter. If the characters are displaying in the same position each time… would that point to something?

[@BrightBlueJim]

In the original pattern, it was all PAIRS of left parentheses. This suggests that each incoming character is showing up as two characters on the screen. Which further suggests that the baud rate is wrong. But the pattern is always the same, which also means that either the UART is always spitting out the same code, or something later in the chain is broken. This could be checked by ensuring that bits coming out of the UART are changing when you send different characters. If the bits are always the same there, then the UART itself is probably bad.

[@melkiorwiseman5234]

Maybe either the transmitter or receiver is set to 5 data bits? I'm not sure if that's possible with RS-232, but if it is then that'd be my first guess. Edit: Or perhaps the baud rates aren't matched?

[@lindoran]

so I have a lot of experience working around rodent feces (i know weird right?) any way 17 years as a field engineer for a telecom you get to clean a lot of that stuff out. Biggest issue is going to be the things that get hot and I hate to say this but the whole power supply and prob the fan have probably still have dried liquids residue that ran under the large capacitors and into the fan assembly... so without getting to graphic (maybe I am already :/) to fully get rid of the smell you may have to strip the large chips and the large capacitors from the board clean under them and then put them back... repairing the other supply might be faster and safer in terms of finding unobtainable parts if something were to be damaged in removal. also the acoustic coupler may have sponge material for dampening inside that may have saturated. Again, sorry for the graphic level of detail but these are the tings I have found in the past.

[@gunnardannehl372]

For the bad smell my recipe is to use ozone on the unit. I bought one cheap open chassis unit from ebay and put it in a box with the object to "clean". Having a timer in the power supply i can leave it on for a day with duty cycle of about 10%. Has great success on moldy or smoker smelling electronics! And you don't destroy anything.

[@mrcampbell7674]

If you can, I'd recommend putting the rat poop boards into an ultrasonic cleaner. It'll hopefully be able to clean underneath chips and other places that normal cleaning can't reach

[@Jeff-ss6qt]

Ultrasonic cleaner along with some sort of enzymatic cleaner if it doesn't destroy anything.

[@TDOBrandano]

And after that maybe lock it in a box with a small ozone generator for a while?

[@tlrptg]

that 6,7 volts on the 5 volts rail probably killed most of the TTL IC-s on all boards.

[@rickhole]

All the 5V chips should be considered suspect. You could pull a couple, put on a breadboard and test them. They may work just fine. Absolute max for 74LS00 supply and input voltage is 7V so you may have squeeked by. At least, the next part you pull from it, do the breadboard test.

[@jwhite5008]

Agreed. Start with the RAM, then all buffers, and then selection logic. Normally I wouldn't recommend blindly desoldering chips, but it's probably necessary here given the overvoltage.

[@BrightBlueJim]

It's worse than that. On the 'scope, he only showed it AC coupled, but if that 6.7V is average, then the peaks are quite a bit higher. They may have gotten 8 or 9V peaks.

[@Scrogan]

Hope he didn’t plug the good boards into the machine with the dodgy 5V rail.

[@BrightBlueJim]

​@@Scroganhe got both from the same source, so the question is whether anybody in the past has swapped them. Highly likely, I'm afraid.

[@a_Fax_Machine]

I am weeks into trying to get an analog video wall processor from the 90s running, and I have to say that your videos have immensely helped me understand what diagnosing a dead machine and following the path of power looks like. You also have taught me perseverance, and to take a break when things seem hopeless. Thank you so much for your videos David, I look forward to your uploads every Sunday.

[@fgaviator]

24:44 Two nibbles 🐇= one byte. 🐰

[@awesomecronk7183]

The little ones are CUTE

[@ToTheGAMES]

THe word nibbles brought back some old memories of NIBBLES.BAS

[@melkiorwiseman5234]

It should be spelled nybbles, to be consistent with byte. 😄

[@Rx7man]

@@ToTheGAMES Yep, and GORILLAS.BAS my first experiences with video game hacking... I actually did do quite a few things in Qbasic with nothing but the language reference help... Trust me it was horrible spaghetti code but it did work!

[@brianhiles8164]

*WORD.* _Represent!_

[@gushiperson]

Take a drink every time he says rodent feces.

[@marcwolf60]

Sllodent... Facezzzzz....

[@johngalt7382]

Pawaenfeces 🤪🤢 *hic*

[@CATech1138]

ACK....at 11am!?

[@theThingsEtc]

Nah. I don’t want to get sh*t-faced.

[@LoneWolf0648]

i choose life

[@enojelly9452]

Fantastic progress! By the way, your scope probably has a serial bus decoder, which may help immensely. If it also has the ability to attach logic probes, it will also have a parallel bus decoder. Displaying both at the same time would be extremely useful, but even just being able to decode the serial data might help you see where the signal path starts to go wrong?

[@R.Daneel]

Might ozone work to freshen it up? You can get (preferably borrow) ozone generators. Put it in a box or small closet and crank it up for a few hours? Ozone's not great to breathe, so don't do so needlessly and keep pets/plants away.

[@francistheodorecatte]

also make sure any of the plastics are removed. ozone degrades plastics very quickly.

[@jwhite5008]

Not at that stage. Even if it looks clean it isn't. It needs complete disassembly and very thorough cleaning with alcohol or bleach where applicable. At least power-washing every part of it is necessary.

[@pd1jdw630]

I think he’s better of with Lysol at this stage.

[@SeekingTheLoveThatGodMeans7648]

An enzyme product perhaps (Nature's Miracle, etc.)

[@jwhite5008]

@@SeekingTheLoveThatGodMeans7648Enzymes can work in theory but I believe they need to be applied for a prolonged time and in a certain temperature range to work. Soaking the boards in non-distilled water for a prolonged period may cause damage to the board and some of the components. Furthermore, I suspect the problem is that he didn't completely disasemble and remove the power supply, which allowed some gunk to be stuck somewhere. Enzymes can eventually break it down but how much time will that take with non-microscopic fragments?

[@TomFynn]

"we got an image, it is nasty and filthy and gross" The CRT has PTSD from the RF.

[@monad_tcp]

RF = rat feces

[@ajsnz]

RF interference

[@TomFynn]

@@ajsnzRodent Feces Interference.

[@BrightBlueJim]

But the nasty and filthy and gross image was on the non-RF unit.

[@Renville80]

One thing I do with plated through-hole boards is just before inserting and soldering a replacement IC, I use a pushpin as a 'mandrel' to ensure the foil in the via is making contact with the hole and not coming loose.

[@bzuidgeest]

You really need some card extenders for a job like this. You have the machine and PCB stock from the tube computer. Shouldn't be to difficult, you could even get the connector from the spare machine. With a card extender, you can probe the card easily while it hangs outside the machine but is still connected.

[@mymessylab]

The DM8812 from the other board could be also faulty. You definitely need a board extender. I’ve counted 22 pins each side. Assuming 2.54 pitch you may find an HP extender on eBay not expensive. You can machine by yourself the PCB and seek for an EDAC connector if you need different pitch. For longer extender you can stack 2 or more of those of HP, if they suit your pitch . Your video content is thrilling me, thanks for that.

[@KeritechElectronics]

"We've got fanspin!" as Louis Rossmann would say :) Looks like that desoldering iron is pretty nice and handy. I think I should get one for my Weller TCP-S iron. And probably retrofit it with a vacuum pump too! Yay, a hacked desoldering station. Tacking wires is the way, I did it a lot when troubleshooting my Soemtron 220 calculator. (Two bunnies playing Pocky game with a straw... It fills you with determination.) "Broken in different ways" is a relatively good thing if you know how things should work in the first place. I had this on the Soemtron and a spare non-working arithmetic logic unit, after some fiddling I got the calc to run while the ALU was partially discombobulated and would work only if I replaced some transistors, so I keep it as a demonstration piece and a spare parts donor. Then, a ferrite core memory failed on me - donor to the rescue! Now I'm working on two Iskra 111 calculators. Power supplies failed and recapped, the machines are so-so working. One has a failing magnet-and-reed-switch keyboard, the other one had a weird bug where digit 3 couldn't light up on all the nixies, that I traced down to a blown transistor in one of these square metal-capped "Soviet Logic Technology" ICs (clearly inspired by IBM SLT). Of course, I traced the issue by substituting a board...

[@gcewing]

Or in this case, "We've got fansmell!"

[@KeritechElectronics]

@@gcewing time to test it with an osmelloscope!

[@TrimeshSZ]

I used to have a VT103 with an LSI-11/23 built into it. That was a pretty good portable PDP-11 demonstrator.

[@markhatch1267]

A very long time ago I worked for a small industrial controller development company as a documentation writer. I remember the hardware fabrication and repair guy talking about slowly heating boards to 100 C and cooling back to room temp (24 hours for whole cycle) to dissipate any moisture in IC packages. Many times this worked for boards that had been operated or stored in places where ambient temp was repeatedly well below normal room temp.

[@EdwinSteiner]

Getting a complete raster of well-formed characters is actually pretty good progress. Now I'm confident you can also make them the right characters.

[@gammarayflash1170]

Before dealing again with all those feces and smell, I'd have repaired the power supply unit. Blergh!

[@AB-Prince]

he mentions in the previous video that the power supply is more or less completely integrated into the chassis.

[@ChristopherHailey]

I love this all of Dave's content but the PDP-11 stuff is special to me. My first experience with a PDP-11 was an 11/03 that looked much like his 11/23 looks like now. This reminds me how fun and exciting it was way back then!

[@todayonthebench]

That change is a step in the right direction. Seems to print more than just 1 type of character now, so that is progress. In regards to the smell, well sometimes a bit of ozone helps oxidize away most things in rather short order. At the downside of also aging plastics and rubber a bit faster. But it tends to remove smells far faster than it causes problems. Just like water rinses away dirt faster than it corrodes metals.

[@jnharton]

Technically, water alone doesn't corrode metals, especially if purified or even distilled. It's probably the combination of an oxygen rich atmosphere plus water.

[@todayonthebench]

@@jnharton Yes, pure oxygen free water is very non corrosive. But largely missed the point of the argument made. The point were rather to dismiss any fears mongering replies like: "Ozone is BAD for plastics! How dare you suggest such madness!" Just like a lot of people make similar stupid comments when it comes to cleaning electronics with water. (or supposedly fixing water damage with rice...) Corrosion is after all a very slow process compared to cleaning. Same for oxidizing volatile organic compounds with ozone relative to hardening plastics in the process.

[@mikejetzer4155]

You might try getting some "Gonzo Odor Eliminating Rocks," which are volcanic rocks with a negative charge. When I buy a used book or computer equipment that's been in a smoker's home, I put the it in a tote with the rocks, open the book up so that some of the interior pages are exposed, put a lid on the tote, and let it sit for a couple of weeks. Totally removes the smoke smell. Never used it for rodent feces, but it claims to remove pet odor.

[@BrightBlueJim]

I would suggest checking that the codes coming out of the UART match what you're sending. If you can send a string of the same character repeated, you should get a stable output from the UART, and by checking the levels of the individual bits, you can verify whether or not they correspond to the character you are sending. Often, when you get characters, but they're the wrong ones, the problem is that the baud rate is not correct, either because it isn't set right, or the circuit that generates the serial clock that gets divided down within the UART is faulty.

[@raymitchell9736]

That's typical for progress to be made. You're doing a great job. I think you should bite the bullet and get the clean chassis working, maybe transplant the power supply? That smell can't be healthy to breathe and it isn't something you want to travel with anyway... Maybe in the exercise of doing the transplanting you'll find the fault? Good Luck with it, I think you're close!!!

[@wtmayhew]

Arrrgh! So many things blitzed, I don’t envy the trouble shooting. That five volt supply ripple on the non-stinky machine is flirting with the limit that TTL can handle without being permanently damaged. TTL can partially fail where it does _something_ but the logic is wrong. It may be necessary to actually dive into the pulse trains to figure out if the addressing is counting correctly. It may be time to acquire an MSO ‘scope or a little vintage Tek/Sony logic analyzer to suss it out. The chips in the stinky machine might be less likely to be damaged, but the odds of traces being eaten through by rat pee all over the place may be difficult to find. Boy!, problem boards either way. Having done a few projects like this over the years, I have respect for the persistence shown in the video.

[@8bitwiz_]

I was a bit surprised that they didn't socket the UART, but at least it seems to be working. The 1013 is the same as the one used in the ADM-3a, with a few other types that are compatible, if it comes to the point where you need to borrow a spare.

[@finkelmana]

If it smells, its not clean. Ultrasonic cleaning would be the fastest way to clean it and get rid of the smell. However, you can put it outside on a hot day. The ambient heat will cause those pee molecules to break down and off faster and float away.

[@jwhite5008]

That is great advice. I'd recommend disassembling the PSU, desoldering radiators, and thoughrougly powerwashing everything powerwashable first. All applicable components including the case need to be scrubbed, then washed with a lot of soap multiple times. The fan probably is not salvageable in terms of smell and needs to be replaced.

[@brianhiles8164]

The reason I watch your context is _because_ I´m fascinated by the matter that old electronics are always broken electronics -- but indeed you prove that such things are formally fixable. _Quantum physics at work?_ In the meantime, you breaking old electronics in a “different way“ is quite entertaining. _Evidence of the Multiverse!_

[@jazzdirt]

Lady and the vagabond spaghetti scene re-enacted by baby rabbits at the end was cute

[@hamesparde9888]

God that multimeter is sexy. They don't do design like that anymore 😢.

[@williamsquires3070]

Yes!! Radio Shack desoldering iron for the win! 😀

[@mwwhited]

Yeah, the bulb des older is cool but the hakko FR301 is amazing

[@8bitwiz_]

Adding the fresh solder first really is important, it adds flux, and if the old solder is lead-free, it lowers the melting point too. It's also much easier with 2-layer boards, if only because they tended to use slightly larger through-holes. But if you know that the old chip really is dead, it might be a good idea to clip its pins first so that you only have to work with one at a time.

[@neilbarnett3046]

I used to mend PSUs, and we would normally mend them on a jig, not a computer. The jig would have the right plugs and some nice big load resistors, so you can get it right without the cost. And I agree, if any of those TTL chips is blown, I wouldn't be surprised. I'm more surprised that there isn't an overvoltage crowbar circuit on the PSU, all the DEC PSUs that I have mended had one, but that was 39 years ago...

[@paulstaf]

I bought an "Ozone Machine Generator 15000mg/h - 3000+ Sq. Ft. Ozone Machine Odor Removal for Home and Car with 120min timer" off Amazon that I use in my kitchen, and car to clear out odors. You could put it in a box with the rodent feces machine and let it go for a couple hours to see if it clears it out.

[@clonkex]

Thank you for using the international date format! If you had used either month/day or day/month I wouldn't have been sure what date it was supposed to be (even though I could figure it out with a bit of thought since I have watched the referenced videos).

[@trooperj9152]

Adorable bunbuns!

[@DrFiero]

A clear acrylic case for the PDP would be super cool!

[@DrFiero]

And if you're gettin' busy with the plastics anyhow... make some blocks with slots so you can display spare cards for each machine!

[@Toby_Q]

Woah, that battle was almost too much... I had to turn my eyes away! Oh the humanity!

[@shinedom]

.. "and with the magic of buying two of them".... 😅

[@derkeksinator17]

If it still smells like shit, it's not clean. The rule that applies to our behind applies to this as well.

[@mikefochtman7164]

Ahh character generating rom. We had a project we read the rom then burned a matching eeprom so we could 'reprogram' the characters. Made all the lower-case into some graphic symbols so we could 'draw' on the screen. Thems were the days of fun hacking! lol

[@melkiorwiseman5234]

Heh. I made a machine-code routine plus data to allow the TRS-80 CoCo to print the IBM character set on its "high resolution" graphics screen (something not supported in hardware) and the program included the ability for the BASIC program to call a "redefine character" command. I never went the next step of making it handle characters as though they were sprites, but it's something I considered. I had almost every feature except that one.

[@SockyNoob]

This is gonna be an interesting set of repair videos. Fixing little by little.

[@senilyDeluxe]

That inverter looks like a 74xx06 to me. Makes it easier to get replacements. The 74LS06 is readily available, if it's socketed, you can yank one right out of your Commodore 1541 disk drive.

[@eischei]

I'd try some enzymatic cleaner. You can get them for pet pee smell as an example, for us it works great if the pet or small kids ever got their feces on carpets, car interiors, blankets...

[@IainShepherd1]

You are a fighter man. Keep going. EIAIN was going to be the name of my cloud-uploaded personality, ah well.

[@GeoffSeeley]

@16:28 It looks like ASCII for "rat poop all over the place" 😆

[@Dont_Gnaw_on_the_Kitty_1]

Looks like more stuck bits, hope you are checking the other rom pins, this is a quick easy check using your scope. Also its bad practice to pull out chips off a working board, get some spares from Digikey. Also these early logic boards dont have esd protected chips. You risk further damage by picking them up with no esd strap.

[@Professorke]

I have also worked on smelly devices, but solved it by making a tank with UVC ozone lamps in it and let the device sit for several hours, you no longer have a smelly smell. Be careful with those lamps, they are very harmful to your health.

[@FordGT40MkIV]

I think you swapped J5 pins 3 & 4 when you probed them as the input should be 5V and the output 12V to feed the ROM. It looks like you could program an EPROM as the character generator and remove all the level shifters in and out to simplify it, assuming there was a reason to go to all the trouble. Regardless, it’s fun to watch you debug this and I look forward to seeing more.

[@mwwhited]

You need a logic pulser for testing gates in place

[@Dsschuh]

I'm thinking that spraying vinegar inside the system might mitigate the rodent odor issue. After that, would the vinegar need to be "flushed out" somehow? Use vinegar mixed with alcohol?

[@jeromethiel4323]

Battlin' Bunnah's. I'd feel bad for them, but a bunny actually bit the heck out of me when i was a child. Those rodent teeth are no joke.

[@gerryjamesedwards1227]

All those little tantalum caps would be worth checking. They fail for kicks, and fail short.

[@jwhite5008]

The 12v and 5v rail on the poo machine look fine, I don't think this is the problem here.

[@Dsschuh]

"Give me anything different!" WOW

[@rpk5568]

See the brd schematic and its IC parts list. SN7400 voltage spec is 4.75 to 5.25 volts, don't expect it to work without a smooth voltage level. But you probably already know that.

[@jennaorlowski5469]

Hardware wise, you can get voltage spikes when the equipment isn't loaded... and not all power supply equipment likes to run unloaded or will not stay stable and may self distruct. Refrence, Guitar Amps.

[@Eatthis143]

I have used a product from Home Depot its about 10 bucks for a gallon and makes about 10 gallons of spray when diluted its called odoban works well on rodent smells.

[@mjdapp]

Looking at the final display you can see that, although there are a lot of minus signs and zeros (not @s) they do, in fact, change in places suggesting data is being read from the display memory. Not necessarily correctly, but it is being read. Meaning that that addressing is probably working and at least some of the display RAM is good and the next problem will almost certainly be related to writing into the display memory. It might be useful to send streams of a single character or pairs of characters to see what happens. Question marks are good for detecting missing bits and alternating * and U detects stuck and/or shorted bits.

[@jwhite5008]

Given how they are written address decoding is also suspect

[@DavidLightman]

well, you got comms working! huge step forward! so it's a bit....less.....sick. and please repair the other PSU you can't use a stinking rat-piss machine, that's gross haha. thanks man! looking forward to the next part.

[@lozahe]

Maybe replacing the fan or dipping it in alcohol might help with the smell. Maybe there is “smelly gunk” left in there. Keep up the awesome work.

[@jnharton]

Plastics can also absorb odors...

[@jwhite5008]

Since he didn't completely disassemble the PSU there is good chance the gunk is on/in the fan itself in the crevices around big heatsinks - exactly the places that are great at radiating smells.

[@nbq201]

Try Simple Green with the chassis and let it soak it may get rid of the smell. And is there some kind of Parity Error going on (E71 vs N81) or speed setting for RS-232? Just a thought.

[@josephsager9425]

Have you considered cleaning the boards with isopropyl alcohol? No idea if it'll help with the smell, but it's strong and safe for board cleaning.

[@RWBHere]

The first thing I would have done after checking voltages is to recheck the data rates. For example, try switching the baud rate down on the terminal, and the computer, since you mentioned a much lower top speed to the one you switched it to. (Was it 1200 baud?)

[@BrightBlueJim]

I think you need to see that +5V bus in DC coupling. Because of the high ripple, that voltmeter is only giving you an average value, while it is the peak value that kills chips. Since you're at almost 7V on the meter, I'm guessing the peaks are at least 8 or 9 volts, which, if so, would make all of the TTL chips, and maybe even the PMOS chips suspect. It was really bad that ADDS apparently did not build a crowbar circuit into their power supply. This was unthinkable in that era. They saved no more than a buck.

[@UnderTrack_]

For the odor issue, you might want to ask your wife about the small odor abosbing grain-boxes-of-sorts they have in japan (it's very common there, there's nearly one in every kitchen but is it's nearly unheard of outside japan), I don't recall their name but they actualy work to genuinely most regular household odors; other than that, I'd advise just ventillating it in constantly fresh/non-smelling air for a very long while, I won't go into the chemical details there either but it's bad odours that stuck back then that are slowly getting loose that give it a bad smell, it's not generating new bad smell (unless it's a poorly smelling slow-paced chemical reaction but that seems highly unlikely); so you just have to vent away all of the molecules of bad odor that still linger to it. (the longer it staid in that stinky place, the deeper that odor infiltration went thus the longer it will take for it to get vented, that's also why washing it doesn't realy work, washing is not only superficial but might not even attack the particular molecules that emit the odor at all)

[@curtislowe4577]

I'm a retired mechanical engineer who is acutely aware of his entirely comprehensive computer ignorance. I greatly enjoy your troubleshooting vids all the same.

[@sparkyprojects]

If the boards you are fighting with were supplied with over 6V, i would just go ahead and order all the 5V IC's and replace them from the start.

[@SeanBZA]

TTL is really robust, that 7V abs max is a voltage that the original ones were given because, during the initial design and testing, that was the voltage where you had a good chance of the input PNP transistors start to break down in reverse, or at least start to leak heavily and not give a good logic level output that was correct. In general they will work at 7V no problem, at least for that era of good old bog standard TTL, and will survive that no problem. Only later processing, where the gates got smaller process nodes, and the later developments, especially the CMOS and the faster versions, would have issues, where they would generally fail pretty much around 8V, but the original TTL would survive that almost unscathed. At least with minimal failures, only ID I had fail from high Vcc, which was due to a failed power supply, combined ironically with a failed crowbar circuit as well, was with a quad NAND gate with 30V rated open collector output, that was the only failed IC on the entire unit, where even the 2708 EPROMS survived, and even the unobtanium Intersil IC's that were used for the ADC/DAC section, and for the main CCD serial memory in the unit. IC's that had rather odd supplies, 12V, 15V, -21V, -18V and -6V being rails there specifically for just the ADC and memory sections.

[@8bitwiz_]

The slightly higher supply voltage will break the voltage thresholds that TTL uses, making it operate incorrectly, but will probably not break the chip. A negative input voltage is more likely to be a bad thing. The LS541 input buffer chip for Colecovision controller ports often goes bad, and for some reason (according to a schematic I have) they used -5 volt pull-downs on the controller port select outputs.

[@SeanBZA]

@@8bitwiz_ Was working almost perfectly at 13V on the Vcc rail, with the only thing wrong was the built in self test did not light for the required 5 seconds self test at power on, to confirm it was a functioning indicator.

[@sparkyprojects]

The supply rail is not a steady voltage, the meter reads the average voltage, the scope shows ripple which could peak higher You not only have to consider the supply rail, but also the max voltage of the inputs I'm not saying all the 5v ic's are damaged, the reason i would change them is to eliminate all possible future problems, maybe even save time.

[@BrightBlueJim]

It's worse than that: while it's possible for TTL chips to survive an overvoltage like that, this is much less likely for PMOS chips, and he said that the UART takes +5V, +12V, and -12V, which a) suggests it's most likely PMOS, and b) is probably really hard to find a replacement for.

[@charuincarnation]

Watching usagi has become part of my sunday morning routine

[@dominicverellen8820]

Hey just so that you know that coaxial port on the back side of the unit is an old school ether network port in either a 10-10 or a 10-100, and if I remember correctly you said that the slowest rate was 100 so that means that it’s a 10-100, and if you can get both of them up and working you could put just a coaxial cable between them and have them network, 3or more and you need either t couplers or a special hub and some hub could switch to 8-pin 10-100 ether network. I know that I might have miss spelled some of that,sorry 😅😅

[@dominicverellen8820]

Another thought is that you might have to try and find one of those other units and take the guts out and put them in your units and you could even get another keyboard out of it.

[@jamesmdeluca]

Greetings: You mentioned a bad 74LS00. The chip that you showed is 74S00 which is logically the same but draws a lot more current.

[@fernando3670rocha]

You might want o use a logic analyzer to monitor your data / address bus or several logic signals for dynamic analisys

[@mnoxman]

"Thou shall check power rails" -- Dave Jones EEVBlog.

[@sloth0jr]

Love that the original keyboard on this terminal was made by Cherry. A shame they no longer make keycaps like that ...

[@katyk9483]

You should get one of the white Chinese desoldering guns with the vacuum in them (clone of Hakko FR301). I used to use the type of desoldering tool you use here and they are way better than braid sometimes, but the vacuum tool is also that much better and well worth it.

[@rsluggy6485]

21:00 I think your your hex inverter is not *outputting* 12V. It is an open collector with no output, pulled up to 13 volts through R14. And since I'm days late watching this, I presume someone already noted that :)

[@OneBiOzZ]

I would very highly recommend swapping the PSU in to the faulty less poop covered unit

[@theelmonk]

The terminal is cute but despite the small screen still bigger than the PDP-11 ! How about a silent 700 instead ?

[@JeffersonGaziro]

I recommend wearing a mask for this kind of work, as exposure to rotten feces could pose a health risk.

[@afberglund2764]

Yes for example a virus that can cause cancer.

[@jwhite5008]

When cleaning - yes, when running and troubleshooting it for hours - mostly pointless

[@christopherdecorte1599]

Steam cleaning might help with the smell. Also try connecting it to a different system the terminal might be working but stuck in the wrong mode for pdp 11.

[@megadjc192]

To get rid of that smell you could try a scrub with activated charcoal. The main challenge is that most smell reducing agents are too caustic for use with sensitive electronics...

[@DVINTHEHOUSEMAN]

For good information on older caps and other things like that I would check out Mr. Carlson's Lab. Very knowledgeable guy and his videos are very informational and easy to understand. Even though he mostly deals with vacuum tube electronics, it's still very helpful.

[@gmt-yt]

A rat could be considered a highly optimized "rat feces machine".

[@jwhite5008]

6.7V is way too high. Absolute maximum VCC is 5.5V for most TTL logic. If the chips were not dead originally - they are now. At least a few of 5V ones almost certainly are. Check the RAM, I would not be surprised if every single one of those is totally dead. If you see >5.5V on the rail, cut the power *immediately* Do not check or measure anything else - swiftly pull the plug. The faster you do it the more chips have chances to survive. The over-voltage is likely capacitor issue - one of them is not "capaciting" anymore, probably output one. But could as well be adjustment potentiometer too rusty to work. 18:55 ROM A1 is unrelated to B1 and so on. But is A1-5 has data B1-4 likely also does. 19:40 the levels are ok, first one was ~11V, second one ~4.5V if I understand correctly. Please check if the dip switches actually work. You might have a bitrate mismatch. Another culprit may be address decoding logic, or completely dead RAM chip. Start by checking the data bus bits that had bad AND-gate-buffer.

[@robot797]

I like those portables they have a look that just works for me and I am glad I dont have to work on them XD

[@runningbird501]

I've found Spray 9 to be pretty effective at cleaning up rodent urine.

[@dsagman]

clearly it has been set to LISP mode

[@scotty3114]

Dang it! You had me holding my breath so I wouldn't smell the rodent feces!😂 I too, would have fixed the clean PS!🤮🤧

[@electrifyingvids3545]

I noticed that you were probing digital signals a lot with an oscilloscope. Yes that method works, but it lacks some features such as analyzing multiple channels at once. If you think you'd be checking digital signals a lot more in the future, I recommend you get a logic analyzer. It would provide more useful data at once than an oscilloscope. Plus it's litterealy designed to trouble shoot digital circuits. Oscilloscopes are more for analog.

[@alexkuhn5078]

22:22 oh cool, you got Mario Paint running

[@mekafinchi]

the buns are playing the bunny pocky game

[@Scrogan]

Sounds like it was getting too close to the maximum voltage for 7400 logic chips. I’d actively investigate every IC that got the 6.7V. Try piping air from an ozone generator into the thing to kill the smell.

[@xephorce]

epic video. love the progress that was made. the bunnies at the end SO CUTE. question for anyone on here. I have a more modern computer ATX power supply that just keeps shutting off randomly. It will power the computer just fine for minutes to hours then just shut off and repeat this for a while until you leave it off for about an hour. Then you can turn it on and it will run for minutes to hours again then randomly turn off. Ive tested with a known good power supply and the computer will stay on for days and never turn off so it is for sure the original PSU that is the problem. I can't find any faults and the voltages test good. I can only think its some component right at the edge of its specs. but does this seem more like a possible capacitor issue or a transistor issue? i rather replace a part then rush to buy a new power supply if possible lol. thanks all

[@nikkiofthevalley]

That sounds more like thermal shutdown or some weird logic error. Also, modern power supplies are much more complex than the older ones that you see on this channel. If you do not have extensive electrical engineering knowledge, you cannot repair a modern power supply without an obvious fault. If you don't know what you're doing, _do not_ open a power supply.

[@xephorce]

@@nikkiofthevalley I've worked on electronics for years and the computers on f-18s in the Navy. So I have some experience. Its just atx psu that throw me off. In the psu I do see 2 components that the have what looks like heat changed the color of the board in the spot. One is a large resistor and the other appears to be a small 3 leg transistor. Not one of the large ones. I was thinking logic or thermal fault but I can't find anything out right. Thank you for the replying.

[@ad5mq]

put some dryer sheets inside and leave it out in the sun. That works great for getting cigarette smoke smell out of electronics and I vet it'd work for mouse poop too

[@derekloudon8731]

Thankfully, we don’t have smell-o-vision! The whole family adores the rabbit videos.

[@dodaexploda]

Where do we buy one of these radio shack desoldering irons? Radio shack doesn't exist any more in Canada.

[@rwdplz1]

74L____'s going bad is definitely a consistent pattern when fixing old computers

[@jnharton]

Nothing lasts forever.

[@imark7777777]

Oh don't feel bad the other one needed to be cleaned up either way. It sucks to work on disgusting things. That's the first thing I usually have to do when working on somebody's computer.

[@charlybrown9024]

Do you think that puting the stinky unit inside a bag and filling it with an Ozone generator could "bleach" the smell?

[@markdjdeenix6846]

good improvement .im finking you need to make a riser card cable maybe two pcbs with ide cable bwtween them to get the cards out the backplane .so you can test .

[@markdjdeenix6846]

im not sure about how many conductors are needed .if not ide scsi would have enough .or a deep pcb riser .PCB WAY

[@SeekingTheLoveThatGodMeans7648]

What's this thing with one input of a nand gate tied with a small capacitor to ground?

[@Rorschach1024]

Hydrogen peroxide as is in color safe bleach, is best at removing odors. Also an ozone generator will too.