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Picked up an incredible Commodore 64c haul yesterday w/ some really fantastic/rare items. However the C64 itself is (mostly?) dead - tips appreciated!

wowbobwow

wowbobwow

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I was recently contacted via my Retro Roadshow website by a lovely older gent in my area. He's recently downsized from living in a houseboat to living in a small apartment, and decided that it was time to "re home" his Commodore stuff. I'm grateful that he picked me to reach out to!

I went and picked everything up yesterday, and spent a fun evening last night just photographing and cataloging everything. He had run a small business and taught himself and his kids programming on this machine back in the 80's, which sort of explains the interesting mix of items and software, much of which leans more towards business usage and programming work than other C64 hauls I've gotten in the past.

I concluded my evening by attempting to boot up the C64c itself, but sadly it's not getting very far. Other than the briefest of flickers on the CRT when I hit the power switch, there's no signs of life at all - no power LED, no drive activity, etc.

Here's what I've done so far:
  • Tested with all three PSU's that were included in this bundle (two of which the previous owner used to run the machine late last year)
  • Tested with a 'known good' PSU that works on my other C64
  • Opened the case and looked over the motherboard - no obvious signs of damage, corrosion, leaking capacitors, etc.
  • Verified that the motherboard fuse looks normal/good
  • Plugged in my SD-to-C64 cartridge and noticed that its LED remains off, except when I hit the reset button on the cartridge - that makes the cartridge LED briefly flash once
  • Let the system sit while powered on for a few minutes, and touched each of the chips - a couple of them get faintly warm, but none of them get noticeably hot
  • I've ordered a "Dead Test" cartridge from eBay, but that won't arrive for a few days at least
I'm much more familiar with Apple II and Macintosh troubleshooting. If you have any tips or suggestions that I might pursue to get this machine running again, I'd be grateful!
 
wowbobwow said:
I concluded my evening by attempting to boot up the C64c itself, but sadly it's not getting very far. Other than the briefest of flickers on the CRT when I hit the power switch, there's no signs of life at all - no power LED, no drive activity, etc.
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Basics first. Get the schematic for the rev of board that you have, and start by verifying that you have the correct voltages on the various voltage rails.

Do you have an oscilloscope?
[EDIT: Hit "send" a little too quickly...]
 
wowbobwow said:
Oh that's awesome! If you ever find yourself with a spare "trap door," I'd gladly buy it off you... :)

Huxley
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I think its best just to accept it as is. Most monitors are missing doors and without 3d printable replacements it just best to leave them as is.
 
You mentioned you tried 3 different PSUs but did you test the PSUs first? C64 power supplies have a bad tendency to over volt on the 5v rail, and plugging in a bad one will damage some of the chips on the motherboard. (In my previous experience, I fried the ram chips so wasn't too bad...)

Seeing that you've troubleshooted Apple II's, you can use the basics from them to help with the C64. The basics to check first are the voltage rails, reset circuit and clock signal.

PS - nice haul! Hope to see the c64 working again!
 
That's a totally beautiful haul. But it does leave me wondering, did you have a look at this book that came with it?
WqarTgL.jpeg
 
Check the power switch for continuity and/or exercise it for a while (with the PSU off). Also the DRAMs do fail on the C64C and if so they can get hot seconds after turning it on.

Dead Test is a good start, but also that book mentioned above has probably almost everything in there people are going to tell you here as well

Good luck, enjoy the nice haul (my favourite is the Super Disk Drive)
 
thorpej said:
Basics first. Get the schematic for the rev of board that you have, and start by verifying that you have the correct voltages on the various voltage rails.

Do you have an oscilloscope?
[EDIT: Hit "send" a little too quickly...]
Click to expand...
Jason:

Hey, great to see you here - not at all expected. I've been lurking for years but slowly joined up and in over some KIM-1 stuff (I've been redrawing Dwight Elvey's lost diagnostic board and 6530 replacement module schematics).

Jonathan
 
Dropping in with a quick update: I let the system sit while powered on for ~10 minutes last night, and noticed that the chips in positions U7 and U9 got noticeably warm - not "hot" or uncomfortable to touch, but clearly warmer than any of the other components on the board.

I've also taken to heart the (many!) suggestions that I test and/or not trust the old power supplies, so I've dug out my old multimeter and I found a "how to" video on YouTube for testing the C64's power supply. I'll be doing the voltage checks this evening - fingers crossed that at least one of these three PSU's is putting out the proper amount of power!

Thanks for the tips and guidance, I'm looking forward to sharing pics of the system running sooner-or-later!

Huxley
 
wowbobwow said:
I've also taken to heart the (many!) suggestions that I test and/or not trust the old power supplies
Click to expand...
The failure mode is particularly brutal (the regulator, which has been helpfully potted in epoxy to ensure maximum heat retention, croaks and dumps unregulated DC onto the 5V rail). MOS's chips are fragile enough as it is, they don't need any "help" from an over-voltage condition :)
 
thorpej said:
The failure mode is particularly brutal (the regulator, which has been helpfully potted in epoxy to ensure maximum heat retention, croaks and dumps unregulated DC onto the 5V rail). MOS's chips are fragile enough as it is, they don't need any "help" from an over-voltage condition :)
Click to expand...
Got it. I've been around C64's (and 128's / Amiga 500's) enough to know that their PSU's frequently fail, but until today I don't think I fully appreciated how fatal to the system those failures can be. I've just ordered a nice modern PSU, which cannot ship fast enough!

I am curious though, does the same advice / warning apply to those 3rd-party "Phoenix" power supplies? I know they're old and may have bad capacitors, but do they also tend to fail in a kills-the-computer sort of way?

Huxley
 
wowbobwow said:
I am curious though, does the same advice / warning apply to those 3rd-party "Phoenix" power supplies? I know they're old and may have bad capacitors, but do they also tend to fail in a kills-the-computer sort of way?
Click to expand...
I don't have any experience with those, alas, so cannot offer any advice about them.
 
I’m back with an update!

You ever have one of those moments where you realize that you’ve been so blindingly stupid that you’ve caused a whole bunch of unnecessary pain and suffering? Yeahhh…

I’ve been tinkering with this poor dysfunctional Commodore 64c for three days now. Given that the previous/original owner assured me that it was working well not very long ago, it really bummed me out that it seemingly died right when I purchased it. Following various bits of advice I’ve received here, on Twitter, on Facebook, and on various other forums where I’ve been asking for help, I’ve gone pretty darn deep (by my standards) trying to bring this machine back to life.

I meticulously followed some excellent YouTube videos and verified both the AC and DC voltages across the motherboard, confirming that none of the delicate traces on the board had been cracked. I also verified that the ancient and failure-prone Commodore power supply is still working within its intended specs, despite their well-known habit of failing and killing C64 systems.

I then carefully removed every socketed microchip and painstakingly cleaned them and their sockets, one pin at a time. I also did a thorough deep-cleaning of the power switch, first with 99% alcohol and then with DeOxit deoxidizing spray. I’ve also ordered a diagnostic and testing cartridge, along with a modern (safe!) replica power supply, all in hope of figuring out what is preventing this lovely computer from starting up.

At every step, I would test and re-test the system, but sadly I could never get anything onscreen beyond a momentary flicker. Try something. Test. Flicker. Sigh. Repeat.

I finally got to the point where having all this stuff piled up on my work desk was making me sad, because *nothing* I’ve done has made one iota of difference, so I spent the past hour carefully packing everything away, and partially reassembling the computer so I wouldn’t lose the many screws that hold it all together.

As I packed the items back into their plastic bins, I carefully unhooked the video cable that runs between the C64 and its monitor, and that’s when I had the startling realization that I’ve tested and cleaned and fiddled with every single component of the computer, but I haven’t validated the cable or monitor.

Mostly in an effort to eliminate a few more possible failure-points from my mental checklist, I tried connecting the computer to a small TV I keep around for testing things. Yellow wire to yellow video-in jack. White wire to white audio-in jack. Red wire to red audio-in jack. Hit Power. See flicker. Sigh. Repeat.

Then it hit me. A moment of stark clarity. What if I tried the other wires into the video jack? I swapped the white in place of yellow, hit the power switch, and PRESTO THE DAMN COMPUTER FIRED RIGHT UP!

In all my years of being a nerd and playing video games and tinkering with old computers, the tried-and-true rule has always been that yellow wire = video, and red / white wires = audio. Apparently this particular cable with this particular Commodore 64c does not adhere to that rule, and all I can assume at this point is that the system was working fine the entire time, and I’m just happy that I didn’t inadvertently murder it while trying to “fix” it over and over and over again.

Lesson learned!
 

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Some C64 have 5 pin DIN video out and some have 8. Atari 800's have 5 pin DIN and there are video cables meant for both machines but wiring is different.

8 bit video out.png
 
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Check the SID (audio) while you're at it, because that can sometimes be vulnerable messing around with the video port. This is more of an issue for the SX-64 than the 64 or 64C, but you probably should check it anyway.
 
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