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Commodore 64 not working

Ozfer

Experienced Member
Joined
Jan 15, 2014
Messages
82
Location
Connecticut USA
I recently picked up a c64. I have the main unit and a power supply. When I go to turn the power on the first time I got the blue box but no words appeared in it. After that I just get a black screen of nothingness when I turn it on but the light does appear on the unit.

The first thing I did was check the power supply. It seemed to be putting out only like 1V ac and no DC so I think the power supply is why it was not working. Now I am having a hard time deciding what to do with the power supply. I cracked it open but as others on the forum have stated its 100% full of epoxy and there is no way to get to the components. I read another website that said you could combine a 9V Euro Snes wall wart with a 2A phone usb charger and that could work but the problem is I live in USA and no one sells European SNES power supplies and even a ebay search didn't find much other then a few CHEAP reproduction psus that cost almost as much as a secondhand c64 psu and only put out like 350mA, and wall wart that don't have the right prongs for USA.

Am I stuck just biting the bullet and buying another secondhand c64 psu or is there a better way to do this?
 

badmofo

Member
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Apr 4, 2012
Messages
36
Location
Melbourne, Australia
Buying a second hand C64 PSU would be the easiest, but they're known to be a poor design and they ain't getting any younger. Next best is a C128 PSU, which is a better design, but again they're getting old and you'll either need to mod it or use an adapter to fit the C64's round DIN power plug.

I made my own recently, using "wall warts". You don't need a SNES PSU, there are lots of 9VAC power packs out there. They came with modems and of course you can just buy a brand new one from any decent electronics store. I tried using a phone charger but it wasn't up to the job, so ended up using a proper 5V power pack. The one I made is working well, details here:

http://www.vogons.org/viewtopic.php...31005a5c8d75f17e419dd7b72bc9&start=80#p412903
 

Ozfer

Experienced Member
Joined
Jan 15, 2014
Messages
82
Location
Connecticut USA
I want to make my own but I dont have a 9vac wart. Unfortunately there are no electronics stores near me and radioshack closed down. I will have to see what I can come up with... If anyone is selling a secondhand psu cheap or are making reproductions please pm me.
 

Ozfer

Experienced Member
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Jan 15, 2014
Messages
82
Location
Connecticut USA
Okay I ended up buying a replacement supply and it tests well but I still have a black screen :(

I have the breadbin model 250407. The only socketed chip in the system is the 6567 and I tried reseating it to no success. I also tested the fuse and that's working properly. No visible damage present to the board.

I have heard a lot of people say the next thing to check is the PLA chip. Should I try this and where would you guys recommend getting a replacement?
 

KC9UDX

Space Commander
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Jan 27, 2014
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Lutenblag
Statistically speaking, yep it's the PLA. Maybe.

If I were you (based on one such C64 I have) I'd make sure you don't have a SID or VIC-II (or anything else) with shorted address lines before putting in a replacement PLA.

The best source for a PLA is a working C64. Else there are EPROM based replacements.
 

Ozfer

Experienced Member
Joined
Jan 15, 2014
Messages
82
Location
Connecticut USA
Hmm does the PLA even make sense though? When I turn the C64 on if I have my datacassette connected I can hear it working and I can even press play and rewind so that somewhat works. If my 1541 floppy drive is connected the unit flashes the red light when the system turns on as it looks for a disk. Unfortunately I don't have any original floppies or tapes to test with.

Since I used to have a blue box with no text is it possible the original power supply could have killed the video or something and is there a known fix for this? Whatever is wrong with it seems to be heavily video related as I can hear the unit toggle on and off. After leaving the unit on for a while the vic chip really heats up and the voltages across the board appear to be normal.
 
Last edited:

KC9UDX

Space Commander
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Lutenblag
Keep the heat sink on the VIC-II! :) it needs it.

The cassette motor is supposed to be off. That tells me the KERNAL isn't initialising zero page correctly. A dead PLA can certainly cause that. So can lots of other things.

The disk drive is a computer in itself. It can fully function without the C64. The computer doesn't actually do anything to the disk drive at startup. There is no automatic boot process on any of the Commodore 8-bits. It's alien for anyone not used to them, but that's the way it is.

The "blue box" with no text could be bad RAM, bad ROM (rare), a bad VIC-II (rare), a bad CIA, or a dead or dying PLA. Actually all the symptoms you've mentioned indicate these same possibilities. It just happens that the PLAs seem to be a common failure point at this point in history. You could almost say it was a poor design. But seriously, they have all lived 5 times their intended lifetimes.
 

Ozfer

Experienced Member
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Jan 15, 2014
Messages
82
Location
Connecticut USA
Okay I ended up buying a prom and sockets for like $3 hope it will replace the PLA... I will report back when I get it in the mail
 

RobertB

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Mar 20, 2006
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Visalia, California

KC9UDX

Space Commander
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I thought you still had to hold the C= key or something but then I suppose that doesn't make sense, CP/M wouldn't work. And maybe that puts it in 64 mode probably.

Probably I never noticed because I only ever used 1541- written disks, and aLways in 64 mode.
 
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