Commodore 64 - help with repair needed


Ian J

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Aug 27, 2010
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I got one of the C64's from @sm0kew0n a while ago and finally got everything set up to run it.

Unfortunately all I got was a screen of garbled characters and then a black screen and that's all I now get.

Anyone know where I can get a diagnostic cartridge and associated cables?

Failing that any technicians around that would be willing to repair it?

Gutted as I have set up a nice little retro play area and dug out my 1541 drive.
 
I think it may be memory, as in most C64s I had with black screen it was a memory.
Generally, use this: http://personalpages.tds.net/~rcarlsen/cbm/c64/c64-ic.txt. This is a very good diagnostic document.
In my C64s once I got one with typical bad memory symptoms - black screen, once around 15 power cycles traces of garbage. Some way it was one of CIA chips.

If you need more help, I'm quite into old computers.
To remove RAM, you can use solder pump (recently I used one with 40W heater built-in - cheap and very useful) or, if you are sure that chip is bad, destructively cut the chip and clean holes. Don't forget about sockets.
 
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Cheers everyone for all of the advice.

Attached is a photo of the screen that comes up when the 64 is turned on. After that when the machine is power cycled I just get a completely black screen until I leave the 64 turned off for a while. I then get the corrupted screen again.

20170413_161944.jpg

Is there anywhere I can guarantee getting memory that will definitely work? Ebay looks a bit scarce for the stuff.
[doublepost=1492127621,1492127447][/doublepost]
To remove RAM, you can use solder pump (recently I used one with 40W heater built-in - cheap and very useful)

Can you post an image to the one you have used

I was thinking of getting one of these as I seem to be doing more repairs these days that require a bit more finesse than a spring loaded de-soldering pump.

ZD-915 Desoldering Station for Circuit Repair 160° - 480° C.jpg
 
The tipps given seem to be pretty good already. I have read that this can also be cause by a faulty charset ROM. But reading the troubleshooting guide linked above, that should only be the area where the normal text is displayed after start up. Check if any of the chips get too hot to touch while you have it running, might give away the culprit. Also check if the voltage levels are correct, may also be a faulty PSU.

Have you pressed on all the chips? If not, do it firmly and reseat any that happen to be socketed.

EDIT: Actually, since the system goes to a blank screen shortly after power up and you have to leave it off for it to display the garbage again, I bet it's the PSU.
 
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I don't know how much this helps, but the old shop I used to use when I bought Acorn kit is still going after all these years, and sells those chips for 5GBP a pop. 40 quid to replace all the ones in your C64 doesn't sound like too bad an offer, and you probably won't need to replace all eight.

http://www.cjemicros.co.uk/micros/individual/newprodpages/prodinfo.php?prodcode=VAR-4264

FWIW, I suspect that image does indicate RAM issues, given the charmap seems to be broken in places. It's possible something in the video hardware has gone pop as well, but I'd look into fixing the RAM first and seeing how far that gets you. I think your PLA is okay, from what I understand of its role in the system.
 
Tested the voltages on the SID chip and I'm getting 4.66v & 11.98v which I think is acceptable.

Looks like I'll be ordering some memory chips.
 
Can you post an image to the one you have used

I was thinking of getting one of these as I seem to be doing more repairs these days that require a bit more finesse than a spring loaded de-soldering pump.

These stations You shown are very expensive... I was thinking about this:
kEG5Nyc.jpg

Recently I was changing 4116 chips in my PECOM 64 computer using this tool.

For years I've been using a tube from old ball pen (use the one with steel tip!) connected with silicone hose to old compressor taken from fridge. Bending hose stopped air to flow. As for makeshift device it was doing its job unusually well.
 
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