Commodore 64 troubleshooting part 2 - dead test and diagnostic cartridge

Part 2 in a 3 part series covering C64 troubleshooting. Continuing on from basic multimeter tests, it's time to look at the dead test and diagnostic cartridges. Will it help with diagnosing the shortboard from last time?
Part 1 here: • Commodore 64 troublesh...
Part 3 here: • Commodore 64 troublesh...
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0:00 Intro
3:48 Dead test normal operation
6:14 Dead test with faulty ICs
13:40 Dead test with minimum ICs
16:06 Diagnostic test normal operation
17:50 Diagnostic test without certain ICs
20:22 Diagnostic harness
23:02 Back to the faulty C64C
25:06 One more simple voltage test
28:15 Closer inspection of the C64C
32:14 Final test and outro
🎞
🔗
C64 Pictorial fault guide: www.pictorial64.com/
C64 schematics: www.zimmers.net/anonftp/pub/cb...
Sven Petersen: tech.guitarsite.de/
www.soigeneris.com/mos8701-cl...
Thanks for watching!
#commodore64 #c64 #troubleshooting

[@deborahberi3249]

There are always one or two very useful tips that one can use to quickly help narrow down an area to focus on...great Video! On to Video 3...-Mark

[@CollinBaillie]

Appreciate that you showed the dead test in real time.

[@AlForte13]

Really good video, I have repaired C=64s since the mid 80's, not so much lately but am getting inspired to take out my old gear and try it again. Thank for the video

[@alphahr]

This is a great video. Been working on Cue and 128 for years and eventually ill get thru these stacks

[@esshahn]

Great tutorial on diagnostics, well done and thank you!

[@eugenekiselev]

Incredible tutorial! Thanks a lot! I would love to find something similar for commodore plus/4

[@donaldblakley6796]

Very educational. Thank you

[@konturgestalter]

loooooove this series

[@jeffreyphipps1507]

I think Noel had a switch where the solder was cracked when viewed under magnification. The result was a semi-loose switch that was unreliable. He re-flowed the solder and was able to make it work reliably.

[@TheRetroChannel]

I did see that one, can't remember if it was the switch or the power connector itself. Intermittent faults are the worst 😄

[@dhammar73]

14:00 - shots fired!!! 😂

[@MindFlareRetro]

Awesome. Love your dodgy Sven Diag Harness. I have a harness rig from an eBay seller (also a hard core forums contributor) that has worked well for years, but I think Sven's is a much more sound design. Coincidentally, I am about to order PCBs and parts to build my own _SvenDiagHarness_ too. OMG, I did a double-take when that MFR Dead Test Flash Codes Cheat Sheet popped up in the video...YYYEEESSS! LOL -- I didn't think anyone actually used that except me.

[@TheRetroChannel]

Ha, believe or not I've never had to use the cheat sheet, never had a RAM fault come up, at least that I can remember. If you watch that segment closely there's a little pop up message that probably only you will understand 😉

[@MindFlareRetro]

@@TheRetroChannel Oh! I meant to sign my comment, Mark².

[@DrDavesDiversions]

31:35 Always amazing the messes people leave. Who does that??? :) How about a label (even for your own benefit) saying "this may be dodgy"? When I was in college, wiring serial lines and the campus phone system, we were diagnosing a problem and found a note from on a patch panel from a previous student employee, *signed and dated*, reading "This needs to be grounded". Respect. :)

[@TheRetroChannel]

Haha, that would be nice and I guess it does happen. But I'm guessing in this case they probably thought they did a decent job 😄

[@DrDavesDiversions]

Fair enough. I just reattached our wooden fence door's handle with two random bolts of different having two different heads from my junk box and tightened them so much that the nuts are embedded in the wood now. I suppose and carpenter that fixes it next will think: "Umm, WTF?" :) There is an *amazing* KZbin video called "Commodore 128 Board Repair - Part 1" on "RetroTech Dan" channel that is the most extreme C= repair I've seen yet.

[@TheRetroChannel]

At least that handle ain't going nowhere. It will probably outlast the fence. Going to check out this C128 video now, sounds like something I'd enjoy 👍

[@DrDavesDiversions]

Mark, do you know of any faults with non-ROM chips that might be found by Piggy-backing, such as 74 logic? We wondered this when four of us did a C64 diagnostic-athon live stream on Temporary Offline's channel.

[@TheRetroChannel]

I've wondered this myself but never tried it. Lemme get back to you on that one

[@TheRetroChannel]

Well I tested it out and the answer is sometimes. With the faulty 74LS257, the machine won't boot and piggybacking a good one on top seems to work perfectly. On the other hand a faulty 2114 SRAM seems to make no difference when a good one is placed on top

[@DrDavesDiversions]

@@TheRetroChannel Wow, nice! Tnx. Our guess was "sometimes" but none of us had ever heard of someone trying, let alone a success!

[@TheRetroChannel]

@@DrDavesDiversions No worries, maybe as I find more dead logic I can do more tests. Originally they just went in the bin, but I started collecting them, they're kind of like little trophies 😄

[@donaldblakley6796]

Hi, a 250425 board. Have you seen replacing 2 rams chips thanks to dead test...no cursor, so I was going to look at u1, but I decided to run diag with harness, all passed, then I shouldn't have I guess, but plugged in keyboard. I could still type. Loaded emulator and it worked, but jail bars. I shut off and tried to reboot... black screen and dead test won't do anything. Pla, vic 2 and cpu are ok in my other 64? Damn I wish I didn't do that... shorted something:(

[@TheRetroChannel]

Sounds like the CIA at U1 was already problematic. So definitely start by removing it and see if the machine then boots.

[@donaldblakley6796]

@@TheRetroChannel hi, thanks for responding. I have already tried removing u1 and socketing. No change. Unfortunately I don't have an oscilloscope, so I guess I'm just going to pick at and pull one chip at a time and try the dead test. So far I've done u1, u2, basic and kernal (left them out of sockets) also did the 2 multiplexers. No change. Again thanks for replying

[@TheRetroChannel]

Yeah without a scope or another working machine to test parts it will be tricky. I'd suspect PLA just based on how often they go bad, but also go back and double check the work you've already done. Good luck with it

[@donaldblakley6796]

Hi, you are right about the scope, but however, I do have another working board that I tried the vic ii , pla and cpu in, and works fine:) voltages are good.. however, can a power switch cause this problem? (I've been watching your videos alot lol) power supply is perfect input, but input on switch is 4.87, and output 4.84, and the other day it was 4.83 and 4.80. Strange. I only use the psu from Kellogg seller. I've tried both, same thing. Ty again. Cheers 🍻

[@TheRetroChannel]

@@donaldblakley6796 That does seem a little odd. You could always check the resistance on the switch, with it unplugged obviously. I think the 3 legs on the switch towards the front of the board are for +5V and the ones towards the rear are the 9VAC. Can't remember which leg out of the 3 is which, but the middle one should be the common

[@piconano]

PIA (Peripheral Interface Adapter) is common knowledge. I've worked with Motorla's 6820 PIA. I assume it's the same as 6520. Am I wrong? I never heard of CIA chip until today! Isn't that just Commodores way of renaming something that already had a descriptive name?

[@TheRetroChannel]

Pretty much, maybe they were trying to avoid a potential lawsuit. A lot of MOS logic chips are just copies of something that already existed, but when you have your own fab downstairs you may as well use it to your full advantage

[@piconano]

@@TheRetroChannel What does MOS stand for anyways? "Mother of S**T"?

[@TheRetroChannel]

@@piconano 😄 It's actually my initials. But I think the company just got the name from metal oxide semiconductor.

[@SeanChYT]

ZX Spectrum comment - HOW DARE YOU!! 🙂