I love that you show all the futzing around, dead ends, and initial circuit misunderstandings. These are the lessons that give the new practitioners confidence that they too can attack these problems, and it's perfectly normal to follow a few fruitless leads before hitting the real problem. Well done Dave!
@Godzilla_Jesus5 жыл бұрын
"You don't want to get into reverse engineering it..." Reverse engineers it, anyway.
@johnfrancisdoe15635 жыл бұрын
Brian Sullivan But not much. Would have been educational to study the circuit even if working perfectly. This battery powered device from 35 years ago manages to run for a long time on a cheap battery. It has some well designed circuits to consume near zero power in standby yet wake up on any keypress without loosing the data from that first keypress. Lots of modern IoT devices fail to achieve this.
@koffibanan30995 жыл бұрын
Super interesting. Love the fact that you went through the whole process. I don't like it when people fix stuff very quickly based on experience (although i do respect them for it) and then assume that you have the same knowledge they do. At some point in their lives they had to go through this exact same procedure and find out for themselves the 'hard' way. This is what troubleshooting is about: fumbling through it, retracing your steps, getting lucky sometimes, but all in a methodical manner. Thanks for the videos!
@SolidStateWorkshop5 жыл бұрын
Great video, Dave. Reminded me of some of your older videos from a few years back. Always enjoy watching your videos regardless.
@famillePuces5 жыл бұрын
Teardown + repair = *thumb up* , great vid Dave! Thanks!
@electronicsNmore5 жыл бұрын
Great video Dave!
@paulmcgrath21755 жыл бұрын
Tantalum caps are the devil. Had one die in my dynamic signal analyzer that kept the crt from working; it was a dead short. Now another one has failed as well, same symptoms. I had one fail in my spectrum analyzer also. Finally, I got a dead Flir A40 that had a blown n-channel fet that burnt some traces because of a shorted tantalum cap; got that back up and running too.
@dreggory825 жыл бұрын
I have been tinkering with electronics for 30 years but you still always manage to teach me something. Thank you.
@MrZombiekiller77775 жыл бұрын
I once had repaired some over/under voltage protection device, and found that voltage on a simple voltage divider wasn't what it should have been and ended up replacing every component in that part of the circuit (two resistors and comparator) and the damn voltage was still wrong. As the last effort I removed a tantalum that was parallel with R2 of the voltage divider and it worked! After I told my coworker what happend he said that I should try putting it back in beacause it was bizzare that the cap was the fault, and after soldering it back in, it still worked... Ended up reporting it as "ghosts issues" hahah Learned so much about troubleshooting from your videos, thanks Dave!
@Graham_Wideman5 жыл бұрын
It was not bizarre that the tantalum was throwing off the voltage divider -- same failure mode as in Dave's video. It was somewhat bizarre that reinstalling it didn't recreate the problem -- maybe the heat or lead-bending cured it!
@MrZombiekiller77775 жыл бұрын
Graham Wideman he said it was bizzare beacuse it was a passive component that died, from experience of repairing other devices we have. Its always active components
@MrNetmask5 жыл бұрын
@@MrZombiekiller7777 slovenc?
@MrZombiekiller77775 жыл бұрын
B Bogataj Hrvat
@evensgrey5 жыл бұрын
Years ago I heard of somebody fixing a DNS failure by swapping a network patch cable. That's something that is physically incapable of fixing that problem, but did anyway. (Networks are weird sometimes.)
@Tech-NO-City5 жыл бұрын
Years of dumpster diving I finally found a working i7 like you with your planted finds.
@perhansson67185 жыл бұрын
8:22 It's raining in Daves lab again ;)
@v8snail5 жыл бұрын
Per Hansson, just spit it out...What are you trying to say?
@deadgaming205 жыл бұрын
@@v8snail ;-)
@15743_Hertz5 жыл бұрын
It's the tantalum. I hate those things. They're always failing on power supply boards.
@tubical715 жыл бұрын
they fail *everywhere*...i recently repaired a RIAA (turntable) preAmp..there had been a bunch of them on the raisl...and guess what, the PS kept failing, 78/7915 run into fail-save. I replaced them all with generic 105°C caps and here we go again, like new....sh!tty TT-Caps!! replace them...every time, everywhere!
@15743_Hertz5 жыл бұрын
@@tubical71 To be fair, they aren't ESR efficient unless you run them close to their rated voltages. But we all know what that means in the long run.
@Vladimir-hq1ne5 жыл бұрын
That Fn that was lit when Alt-Fn was pressed in DEC VAX times :) What a great reminder that I'm almost 50 y.o. :) Thank you!
@amandaporter95995 жыл бұрын
Gotta admit, when I first saw this guy I was put off by his voice. Now though, I not only have a great respect, but actually find him refreshing and entertaining!! Obviously knowledgeable and passionate. It great you give your time for us. Much appreciated, and keep ‘em coming ! Ps. How about telling us a bit about yourself? You’ve got a lot of fans out there
@tubical715 жыл бұрын
he actually did...watch older videos and also EEVBlog 2 :)
@chriswatson24075 жыл бұрын
'just wanted to use the IC tester'. Yeah buddy, I believe you.
@gmonkman5 жыл бұрын
Need to diagose kb problem on zx specy, this is a great walk thru for a novice like me. Ta for your work!
@McTroyd5 жыл бұрын
But Dave, you totally missed a chance to blow up a tantalum! THINK OF THE VIEWS!!! (j/k)
@InsideOfMyOwnMind5 жыл бұрын
Over voltage on tantalums is an absolute party.
@leisergeist5 жыл бұрын
Capacitor fireworks display! Woo!
@Ziferten5 жыл бұрын
Think of the SMELL! Yuck, that burny metallic scent takes forever to dissipate.
@leisergeist5 жыл бұрын
@@Ziferten The smell is somewhat "tantalizing" to some people. I'll show myself out.
@McTroyd5 жыл бұрын
@@Ziferten He's on an island continent, nearly on the other side of the world from me. If that smell propagates THAT far, I'll be genuinely impressed.
@pr0engineer8735 жыл бұрын
Thou shalt check Tantalum caps.
@markcummings1505 жыл бұрын
That's an unusual failure mode. Most tantalum cap faults I've found were short cct. Sometimes blowing the top of the caps off which makes it a lot easier to find.
@0x8badf00d5 жыл бұрын
Sounds like a related failure. There's not much that can go wrong if there's a 1M resistor between the cap and the PSU. Not sure why it's voltage dependent though.
@WacKEDmaN5 жыл бұрын
nice one Dave..glad you did the visual inspection first!...altho...them solder joints looked great for such an old bit of gear...
@johnfrancisdoe15635 жыл бұрын
WacKEDmaN Made by professionals, not amateurs.
@regmigrant5 жыл бұрын
build Mr Carlsons capacitor tester :)
@EEVblog5 жыл бұрын
What's the deal with that? I've gather it's controversial in some way?
@McTroyd5 жыл бұрын
@@EEVblog He's managed to figure out how to test caps for leakage, and potentially predict a future failure. Whole thing done with batteries, instead of the old-school high voltage testers. I understand the plans are on Patreon, which might be the "controversial" bit. Video here: kzbin.info/www/bejne/gpnSp4V_gpqrd9E
@wolvenar5 жыл бұрын
Not sure how fit it is for low voltage systems such as these.
@denny99315 жыл бұрын
@@EEVblog Maybe it is the analog witchcraft making it controversial :D
@God-CDXX5 жыл бұрын
@@EEVblog i built one they are the ducks guts
@DrewskisBrews5 жыл бұрын
Mr. Carlson's Lab on KZbin designed an advanced cap tester that will check for leakage like that
@TheEPROM95 жыл бұрын
I am intrested in building it but the details are only avalible to his patrions.
@hobbyelectronics66305 жыл бұрын
@@TheEPROM9 for $2 a month it is worth it. I built the cap tester and it defiantly would have detected the leakage in that cap.
@Mosfet5105 жыл бұрын
He has some different testing jigs. One is an old scope that shows an L or some figure for diode checking I think.
@hobbyelectronics66305 жыл бұрын
@@Mosfet510 It is a curve tracer or an octopus circuit. It is similar to a Huntron Tracker. It plots voltage and current on an old oscilloscope. I haven't built it yet, but it is a simple circuit. They have been around for decades and are kind of an insider secret for repair techs.
@l3p35 жыл бұрын
I do not even build anything of it but still think that *at least* 2$ each for Dave, Paul and Clive is a *must* for anyone learning about electronics!
@andreykldjian5 жыл бұрын
i really enjoy these repair videos along with the soldering videos.
@RoelvandenBergWillemWasbak5 жыл бұрын
People, if he started with the tantalum and replaced it directly he wouldn't have a video to post. I enjoyed it.
@AmRadPodcast5 жыл бұрын
Ah the PCjr. Learned to program in BASIC on that puppy.
@aaronwilliams12495 жыл бұрын
I had one of those as a kid. I did a lot of programming on it. I had the technical reference manual and did a lot of low-level programming on it. I built a controller to add a second floppy drive and I had an adapter to use a PC XT keyboard. I learned Turbo Pascal and assembly language on that machine. I wrote a lot of software on it.
@Darkendvoid5 жыл бұрын
Dave, the methodical videos showing how you would test the components are great, make me wish I pursued EE instead of Network/Desktop engineering.
@EEVblog5 жыл бұрын
Thanks. Seems everyone just wanted me to replace the caps and be done :-/
@Broken_Yugo5 жыл бұрын
Always nice to see some proper component level troubleshooting rather than shooting in the dark. If I wanted to see hitting the common troublemakers by rote until it runs and wondering what the hell actually fixed it I'd just record my own bench.
@GlennHamblin5 жыл бұрын
Kamagatza Bob's your auntie! Great troubleshooting vid. Thanks Dave.
@melkiorwiseman52345 жыл бұрын
The only keyboard I ended up repairing turned out to have a mechanical rather than an electronic fault. One key kept on repeating, as though being held down. After taking the kb apart and examining the mechanics, I found the problem. The metal bracket which provided the spring return for the key was just slightly kinked. It was barely noticeable, but it was enough so that the bracket was pressing down on the conductive rubber mat and making it contact the PCB track so it appeared as though the key was being held down. I removed the bracket and smoothed out the kink and that was the repair.
@GreenAppelPie5 жыл бұрын
Alright this was enjoyable, it took me back, it make me wanna go fix stuff again.
@sanosanbaby5 жыл бұрын
I just love your repairing videos
@hadireg5 жыл бұрын
Loved this investigation!! now I know many on the bad cap effects! Thanks Dave!
@ZILtoid19915 жыл бұрын
The main issue with that keyboard was the bad stabilizators. My BTC also works on a similar conductive rubber dome over PCB design (but with Cherry MX compatible sliders), but at least the wire stabilized keys worked very well after a good clean - which meant complete disassembly, and a bath in a warm, soapy water. The pin stabilizers needed some lubricant in the form of some universal grease (which I also applied to the wire stabilizers), the result was the best feeling keyboard I've ever owned. Probably some better Alps switch would outdo it in almost every way, but I couldn't try any of those.
@muzzaball5 жыл бұрын
I like watching you work!
@kmonyt5 жыл бұрын
Love these troubleshooting videos!
@derofromdown-under28325 жыл бұрын
Great find Dave, well done!!! 10/10
@pahom25 жыл бұрын
And the expensive tantalum cap was put there for better reliability
@johnfrancisdoe15635 жыл бұрын
Tcll5850 Nope, smaller and more expensive than electrolytic cans back then. They were a luxury component only used when the special properties were needed. Also back then Tantalum wasn't a conflict mineral.
@ligius35 жыл бұрын
Good troubleshooting video in the mixed domain and quite concise.
@krnlg5 жыл бұрын
Great video, always nice to see troubleshooting and repair like this! :)
@rafflesmaos5 жыл бұрын
Hey Dave, in case nobody else pointed this out yet, the reason for a 0.8mm pcb is most likely because they used this thickness in other keyboards of the day that used buckling springs and capacitive sense. In those boards, the pcb had to be curved, hence the need for flex. I suspect they probably just went with whatever they were used to at the time, even if the flex was not needed here. The PCjr keyboards (both of them) were a bit of a disaster.
@flomojo2u5 жыл бұрын
Hat's off, Dave! So great seeing logic ICs and troubleshooting that found a real problem after all that weird behavior.
@richardbrobeck23845 жыл бұрын
glad you got fixed i have issues with those caps before
@TheEPROM95 жыл бұрын
I approve, another bit of vintage computer hardware brought back from the dead. Tanterlums, transistors & diods are ususly the first things I check, caps, depends on when they were made or the type. 60s- valve stuff, early 90s to late 80s & mid 2000s just replace. If its outside those known bad periods then I tend to fire up & test. Good video tracking down the problem & solving the real issue.
@DC177E5 жыл бұрын
Great video as always Dave!
@jameshorn78305 жыл бұрын
I think Dave should make a video on how to interpret Australian sayings... I mean I sort of get them, but more explanation would be great. Dave would probably just insert more sayings into his explanations... Fun times to be had...
@bukitoo83025 жыл бұрын
Hi! SYC is an Argentinian Company that sells electronic components. It as funny that you've downlaoded that ds. LOL
@Atelierul294 жыл бұрын
Watch out! The alien on your ceiling started drooling! What's that goo from 8:21?
@krz88888885 жыл бұрын
love the repairs Dave, thanks!
@mamalala87235 жыл бұрын
The ~400 kHz sounds like the carrier signal for the infrared, which is then modulated by the bit pattern of whatever key is pressed (turning on/off the carrier signal to the IR LED's as needed). Maybe you could do an episode about how IR remotes actually work (gated carrier on the TX, narrow bandpass on the RX), and why some early systems were prone to random receptions by just having sunlight shining on the receiver.
@lupinedreamexpress5 жыл бұрын
I have to comment about the traces on the board. I have a mixture of 'what where they thinking' and 'oh my god that's art' running through my head, in reference to all those trace paths. guess it was easier to manufacture if nothing was precise. Gotta appreciate the beauty in these things...
@NetworkXIII5 жыл бұрын
Lupine Dream Its amazing how well some of this old stuff performs with these one or two layer PCBs and no ground plane.
@The.Doctor.Venkman5 жыл бұрын
I really enjoyed this video - Well done Dave!!
@paulfrankovich30855 жыл бұрын
That was some awesome troubleshooting. I know you said this could have been faster but I’d love to do this stuff. Awesome video. New Sub.
@gkmaia385 жыл бұрын
i really like when you do these repair videos!
@waynethompson84165 жыл бұрын
Dave, I see what you mean! I did a search for the schematic for the keyboard. I found a good "manual" on the Jr but although there WERE schematics for the main board, the power supply, the modem, the monitor, etc. there was NO schematic for the keyboard!!! There was a fairly decent block diagram for it, but no schematic. In case you want to view it here is the link: file:///C:/Users/user/Downloads/PCjr_Technical_Reference_Nov83.pdf Also, another of your viewers suggested that you build Mr. Carlson's Capacitor tester....I TOTALLY AGREE !!!! The thing is awesome!!! I checked his KZbin site and it seems that the information for that device is limited to Patrons ONLY, so you would have to become a patron to get it, but it is WELL WORTH IT !!! His non patron site is listed as "Mr. Carlson's Lab" and you can find it here: kzbin.infovideos I may have found a link to the regular site that is about the tester: kzbin.info/www/bejne/gpnSp4V_gpqrd9E Check that out and see if it is what we were talking about.
@0x8badf00d5 жыл бұрын
The link ...
@waynethompson84165 жыл бұрын
@@0x8badf00d looks like the path to my hard drive was listed instead of the link. Try this one: ftp://bitsavers.informatik.uni-stuttgart.de/pdf/ibm/pc/pc_jr/PCjr_Technical_Reference_Nov83.pdf
@laurentthommet83135 жыл бұрын
Great video!!! Greetings from France Laurent
@stephtronix18115 жыл бұрын
Awesome fix!!
@skjerk5 жыл бұрын
I love repair videos!
@drivejapan62935 жыл бұрын
Interesting to see the thought process of an engineer doing repair sometimes. In some regards its very different from a repair tech. Though I assume some of Dave's process was for the added educational video content as well.
@mschluetter5 жыл бұрын
Can't unsee the spit flying at 8:20
@JanaBuvari4 жыл бұрын
that was an awesome troubleshoot! Tubular!
@3Dparallax5 жыл бұрын
BUT YOU NEED TO REPLACE THE CAPACITORS /s hahaha, this is classic. Awesome circuit with the wake up circuit.
@davepauljones5 жыл бұрын
More like this Dave
@PilotPlater5 жыл бұрын
This is what you get Dave for hoping my next project doesn't work ;)
@adambailey15265 жыл бұрын
great video dave.thanks mate...
@evensgrey5 жыл бұрын
I think it's not just the leaky tantalum cap and the high-value resistor, but that in combination with the ultra-low input drain CMOS logic. If you had that much leakage current with a TTL setup, it would probably not be a problem. That would probably be what Dave meant about it being fine in another circuit design. (It would make for absolutely sucky battery life to use TTL on a battery powered keyboard, of course. That's why they didn't.)
@Mosfet5105 жыл бұрын
Nice debug! I'm a pretty patient guy, sometimes, but at one point the window might have looked good for a quick fix for jr. A tantalum!? lol jeez.
@SuperStststststst5 жыл бұрын
8:22 liquid falls in right hand corner of bench
@guillep2k5 жыл бұрын
Hey, I buy my components in SYC! It's a small electronics shop in Buenos Aires.
@andyhello235 жыл бұрын
Reverse engineering a product must be interesting. Even though this is pretty basic product, was interesting to watch.
@richardgoebel2265 жыл бұрын
Educational and entertaining, too. Winner, Winner, prime rib dinner!
@EmilHarder5 жыл бұрын
What a video. Thanks!
@elguinolo73585 жыл бұрын
You must have some kind of enhanced PCJr keyboard, the one I knew was a chicklet keyboard, most horrendous.
@ilijavk5 жыл бұрын
Hi Dave, these contacts looks good but thay can be gold. Search on youtube electroplating gold contacts, and plese tell us what you think about procedure. Maybe some review. Thank you!
@0xc0ffea5 жыл бұрын
Great video, real edge of the seat stuff. More !!
@ghostrider0905 жыл бұрын
Why use the µA range if you're going to short something out? surely the risk of blowing the meter up is much higher in µA range than when using the full A range? Because of burden voltage maybe?
@frozenfrogz5 жыл бұрын
I hate tantalum caps and avoid them like the plague. Even new ones can fail on you after a short time without warning and failure modes are totally unpredictable. I have had ones that started leaking, some failed shorting a rail and others failed open circuit. Add to this the shittiest conditions of mining the resources needed to make these and you end up with the worst components imaginable.
@evensgrey5 жыл бұрын
I don't know if anyone has pointed this out, but while that keyboard may seem low quality compared to other IBM keyboards from the era (and it is, tbh), it's actually the really nice keyboard for the PCjr. The standard one was a chiclet keyboard. Apple makes nothing but horrible keyboards now, but they're still not as bad as chiclet keyboards.
@carlossantiago48455 жыл бұрын
Great video. I have PCjr keyboard that does not work. I will take a look at it. Maybe it has the same problem.
@kabkab84415 жыл бұрын
I remember the IBM PC jr. GOOD JOB!!!
@jjjacer5 жыл бұрын
@8:22, what just fell on his desk, drool, or something from the ceiling (right below the green power wire on the right)
@eerrefled5 жыл бұрын
Spittle from when he said "trace"
@ricardoacostatorres13505 жыл бұрын
HAHAHAHAHA I NOTICED
@EdEditz5 жыл бұрын
It's snowing in Oz land :) or dandruff maybe ^^
@DumahBrazorf5 жыл бұрын
It's from the Alien hanging on the ceiling...
@spacepirateivynova5 жыл бұрын
when i first heard the problem i thought: there's gotta be some kind of latching circuit that's switching off the IRLEDs but not switching over to allow the wired setup to work, which relies on that circuit to know when to unlatch the first circuit to switch the IRLEDs on... and i was thinking: bitrot? stuck latch or flip-flop?
@punker4Real5 жыл бұрын
It's very easy to remove the yellowing if you want to do so
@00Skyfox5 жыл бұрын
What dropped onto the bench at 8:21?
@rigoligorlc47955 жыл бұрын
Seems I'll have to check the tantalums on one of my not booting laptops.
@senorjp215 жыл бұрын
There is no ground plane or shielding. I wonder if a modern office environment with switch mode power supplies, etc causing something to float.
@chrisboyce50095 жыл бұрын
"With no cap. May not actually be the cap, may be something else. But the cap is making is worse." Which is why I went into software :)
@johnfrancisdoe15635 жыл бұрын
Chris Boyce Do you regret it? Capacitor failures are so much simpler than debugging intermittent failures in complex production code.
@AliHSyed5 жыл бұрын
8:21 *SAY IT DON'T SPRAY IT!* lol
@gertnutterts9885 жыл бұрын
I think allot here will have had the joy of repairing old vintage computers. Watching you do your magic on that jr keyboard was amazing to watch. :) The only thing I don't understand is, was that resistor there as a way of coping with tantaal failure mode? I've had the polarized buggers catch fire on me more than once. :/ Or had it another function?
@tubical715 жыл бұрын
when i need to look up old TTL/CMOS chips datasheets the 1st couple google hits are ususally pdf from old, and lovely, TI datasheet scans converted into .pdf......wired that your search resuslts are so different....
@NetworkXIII5 жыл бұрын
TubiCal The TI website is pretty good also, usually my first stop.
@Taluvian5 жыл бұрын
I assumed cap was issue, and was right. :)
@EdEditz5 жыл бұрын
4:25 that socket in the left upper corner looks like a skull. :) Maybe it's a sign....
@serviciobsas5 жыл бұрын
Syc is an Argentinian electronic store! I buy chips there
@e74av5 жыл бұрын
Great video. Showing so much : )
@Northbaylandscaping5 жыл бұрын
Nevermind reverse engineering and ask yourself why anyone would want to fix a PCjr keyboard to start with...... lol Good video though
@adrianbiankin5 жыл бұрын
Hey Dave, I was looking through the old analogue tv channels on my old crt portable and I found some signals that were interesting like on channels 59/58, 5a and 3 (As off Gosford Area). One of them had a black screen another had scrolling lines and the other had a grey screen. What’s happening? I thought the Analogue signal is gone?
@kiko_meeko3 жыл бұрын
Will an RJ11 to USB adapter cable allow you to use this keyboard on a modern computer? Thanks!
@ServiceComputers5 жыл бұрын
Second Rule of Vintage Electronics: Thou shalt change caps.