Commodore 64

[Hedgeyourbets]

Ok so I got a commodore 64 earlier with the tape deck and a few games for £2
Obviously this is way too cheap for it to have been working, even if the guy selling it didn't mention that fact...
So basically, anyone have any idea how I would go about repairing it? and indeed how much it would cost?
The problem is simply that the screen is black when you turn it on through the RF cable and when i plugged it in with my Megadrive RGB cable (perhaps different wiring I don't know but it fit perfectly) The screen was black still but in addition to that there were some bizarre loud noises too. Anyone have any idea where to begin with A: working out exactly where the problem lies and B: fixing said problem

[KH2K4]

RF should be universal i've used a SMII on one before, it uses channel UHF 36 irc, try twisting input connector till you get a picture, it takes a while to wiggle it into position where you eradicate the noise and fuzzyness.

[Hedgeyourbets]

Thanks, but definitely not an RF problem, the cable was unplugged directly from one of my SMSII consoles and straight into the commodore 64

[alecjahn]

The PLA chip on these is known for going out. Not sure if anyone makes a repro of it anymore.
Does the screen flash when you turn it on using RF?

I know some older computers/consoles have an RF signal that might not be strong enough to activate an automatic RF switch, such as the one for an NES or MD. If this happens to be the case, you'll need an old manual RF switch box. (Like this Atari one)
That being said, I don't know if the SMSII RF box is automatic or manual, so I may be wasting my breath. If it's a manual style, then nevermind! :P

Since the C64 has a built-in RF modulator, you can use one of these little adapters with a standard RCA cable.

The AV plug pinout is not the same between the Commodore and MD.

[Hedgeyourbets]

The RF cable is just a straight console-tv with no switch boxes like the ones which came with N64s. All that happens when i switch it on is that the screen goes from static to a black screen, the power light on the console is on and the data cassette drive starts going if the play button is pressed down. I did a quick search for that chip and that could be it but apparently it could also be some other chip too.

[Bad_Ad84]

http://www.faime.demon.co.uk/retro/cbm.html

some diagnosis steps

[alecjahn]

Ah, I see.

Maybe open it up, leave it on for a few minutes, and see if any of the RAM chips are noticeably warmer than the others?


EDIT: Bad_Ad84 beat me to it. Run though that doc.

[Hedgeyourbets]

Nothing out of the ordinary with the RAM chips and I tested the power supply with a multimeter, all seems well there, tested all the fuses everything was fine, I removed the SID chip, no change there. So I'm thinking it's either the PLA chip as suggested earlier or the VIC chip. The PLA seems to be the most common one to go wrong but neither are exactly easy to obtain. I'm vaguely considering just selling the lot but I am extremely reluctant to do so

[Bad_Ad84]

Rewind bits has some of the chips.

[7Force]

BTW, the C64 doesn't do RGB. You can make a custom S-Video cable, though.

[Hedgeyourbets]

I realised it probably doesn't do RGB, but the tv would just have used the composite signal had the pinout been the same as the megadrive. It's fine though I've already soldered some composite cables to the pins of the AV socket, temporarily. Whether or not I create a more elegant solution depends upon whether I can repair it or not. Also, thanks for the tip about rewind bits, but it would appear that one of the chips I need is out of stock and the other isn't on the list at all, bummer :(:(

[Retrology]

Clutching at straws here but could it be a TV issue, is it a modern flat screen one?

[Hedgeyourbets]

Nah, tried it on 2 22" CRT Tvs, a 14" CRT and a 19" LCD, 100% not a TV issue

Anyone have any ideas, or know of a forum where they're more versed in commodore 64 repairs?
I replaced the PLA chip with no joy and all the ram chips get warm, but no warmer than any other and my master system ram runs hotter than those

[goldenband]

Have you looked at Ray Carlsen's site or docs?

http://personalpages.tds.net/~rcarlsen/
http://personalpages.tds.net/~rcarlsen/cbm/c64-ic.txt

Really nice guy, too. He fixed the C64 that belonged to my girlfriend's late father, and did a great job for a very reasonable price (though if you're in the UK that's obviously not practical in this case). If you get stuck, he might be willing to chat.

[H360]

Don't get rid of it. Everything can be repaired. Just takes a while to find the issue first.

[Hedgeyourbets]

I certainly wasn't planning to get rid of it, binning it would waste the money I paid for the new PLA chip as well as the time i took replacing it, I'm in this for the long haul :P. I have seen his site and tried to follow his guides to the best of my abilities,I'll email him though.
I'm relatively sure that it's the VIC chip now, I can't seem to find a PAL replacement though. Does anyone know if a US chip would work in a PAL machine, I know they're slightly different.

Edit:
Dont worry haha, I found some PAL ones.
Which would be better for me to use, ceramic or plastic, they're the same chip I think, what's the difference?

[Druid II]

Anyone have any ideas, or know of a forum where they're more versed in commodore 64 repairs?
I replaced the PLA chip with no joy and all the ram chips get warm, but no warmer than any other and my master system ram runs hotter than those

http://www.lemon64.com/forum/

[Hedgeyourbets]

Ah, great, thankyou :)

[Yoder]

Make sure to pull the 6581 SID chip and try to boot it. The last Commodore I got had a BAD SID and a bad PLA. The SID was internally shorted and wouldn't let it boot with it in there.

I have another that is booting to a black screen and I've swapped the SID, PLA, and VIC from known good ones with no luck. Could be a RAM chip, I suppose but I think at this point that one was used as the PLA donor for the other one...

You'll most likely end up buying another commodore to get parts to swap and test/fix this one. Then you'll end up having several before you know it ;-)

good luck and Lemon64 is the place to go...just do your homework first before you post there :-)

[MN12BIRD]

I will say this for you and anyone else here with a C64 and no AV cable. I have two C64's and they both have a different AV out port. They're both breadboxes but one has the color Commodore64 logo and the other the plain silver Commodore font without the color rainbow. IIRC one has a center pin in the DIN connector and the other doesn't. My Sega Genesis model 1 AV cable does work on the one without a center pin. Keep in mind this is the mono composite cable, not an RGB cable. The white RCA jack ends up being the video and the yellow the audio so it's not wired perfectly but it works!