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View Full Version : request for help with broken c64?



rebeltaz
January 6th, 2009, 11:11 PM
I tried to PM ChannelManiac (as suggested by wmmullaney) but I didn't get a response. I'll post it here in case he (or anyone else) can help...

I could have sworn that this thing worked the last time that I tried it - several years ago. I went to use it a few weeks ago and the red power LED came on and then went out. I tried to measure the voltages on the power supply, but I couldn't find anything on any of the pins. One of the guys here, William I think, sent me another power supply. The power LED did the same thing. Come to find out, there were some cold solder joints on the mainboard at the switch and the power input jack. After resoldering those, the LED stays on like it should. I don't know what I was smoking when I tried to measure the original power supply I had, because it works fine and all of the voltages (or rather both) or where they should be.

Anyway, I hooked the C64 up to a TV and turned it on. At first, there was a solid green (I think) screen that never went away and the system didn't boot. So I turned it off, waited a minute and then turned it back on. 99% of the time, doing this, I got a blank screen. Once or twice I got the solid color screen. Now, no matter what, all I get is a blank screen.

I tried reseating all of the socketed chips, with no effect. Then I figured if there were cold solder joint in that one section of the board (which looked fine to the naked eye, by the way), then maybe there were others that I was missing. So I resoldered the entire board. I assume that these older chips are more sensitive to static and heat trhan the modern ICs that I am used to working with, so I made extra sure that there was no static and that I didn't overheat the ICs. Still no effect.

So here we are... I was wondering if this sounds like the PLA chip that I have read about or it it sounds like something else. If it is that chip, where can I find one?

Thanks...

patscc
January 6th, 2009, 11:17 PM
See if you can match your symptoms to something in the list here
http://personalpages.tds.net/~rcarlsen/cbm/c64-ic.txt

patscc

channelmaniac
January 7th, 2009, 06:16 AM
Sorry.

I'm on a lot of forums and if I overlook a message it's not intentional.

Put a game cart in it and see if it plays blindly. If it does, check the PLA chip or the VIC II chip. If it doesn't, check the PLA chip first.

Those symptoms can be caused by a bad 6526 CIA, 6510 CPU, 906114-01 PLA, 6567 VIC II, a bad RAM, Kernal ROM, or a short from the RFI shield to the bottom of the board.

The PLA chip is the most likely cause.

RJ

gerrydoire
January 7th, 2009, 06:23 AM
Sorry.

I'm on a lot of forums and if I overlook a message it's not intentional.

Put a game cart in it and see if it plays blindly. If it does, check the PLA chip or the VIC II chip. If it doesn't, check the PLA chip first.

Those symptoms can be caused by a bad 6526 CIA, 6510 CPU, 906114-01 PLA, 6567 VIC II, a bad RAM, Kernal ROM, or a short from the RFI shield to the bottom of the board.

The PLA chip is the most likely cause.

RJ


I recently seen a Very Nice Condition C64 go for $29 on EBAY, so with that in mind, if my C64 was having problems, I'd have second thoughts about trying to fix it, probably just as well to buy another one on EBAY.

wmmullaney
January 7th, 2009, 06:23 AM
If it boils down to the rom, I might have a spare 64 rom chip somewere.

rebeltaz
January 7th, 2009, 08:08 AM
Sorry.
I'm on a lot of forums and if I overlook a message it's not intentional.
Put a game cart in it and see if it plays blindly. If it does, check the PLA chip or the VIC II chip. If it doesn't, check the PLA chip first.
Those symptoms can be caused by a bad 6526 CIA, 6510 CPU, 906114-01 PLA, 6567 VIC II, a bad RAM, Kernal ROM, or a short from the RFI shield to the bottom of the board.
The PLA chip is the most likely cause.



If it boils down to the rom, I might have a spare 64 rom chip somewere.

@ChannelManiac: No problem... didn't take any offense :)

Other than the game cartridge trick, there's no other way to test the chips short of swapping them one at at time, is there? I have cartridges for the VIC-20, but not for the C64 :( I've searched everywhere, but I cannot find anything definitive as to whether or not the VIC cartridges will work in the 64.

tezza
January 7th, 2009, 08:53 AM
Ray Carlson's guide (linked by patscc) is pretty good. I've used it myself to diagnose the most likely chip at fault, and solder in a replacement.

You could either use that guide and replace the suscepted faulty chip. It's not definitive of course so there is some risk it is not the IC at fault. I found it to be correct in the C64 I repaired.

Alternatively, as others have mentioned, second-hand C64s are a dime a dozen.

There is a certain satisfaction to fixing your own machine though.

Tez

frozenfire75i
January 7th, 2009, 09:39 AM
I would save your self the trouble and just find a working C64, after all they were the most populer "computer" of all time sold 10's of millions!

BG101
January 7th, 2009, 07:09 PM
That's not going to be a solution when the supply of second hand C64s dries up though, is it? If we can fix them, we at least have a hope of keeping them going for as long as possible :(




BG

rebeltaz
January 7th, 2009, 08:39 PM
That's not going to be a solution when the supply of second hand C64s dries up though, is it? If we can fix them, we at least have a hope of keeping them going for as long as possible :(

BG

I agree wholeheartedly. I would much prefer to repair than replace!

channelmaniac
January 8th, 2009, 05:32 AM
That's not going to be a solution when the supply of second hand C64s dries up though, is it? If we can fix them, we at least have a hope of keeping them going for as long as possible :(




BG

I have a source for at least a few hundred more dead C64s to part out so parts will be around for several more years, even at the rate I'm selling them worldwide. (These are all ugly, abused, beaten, and dead systems from a defunct repair center)

RJ

wiskow
January 8th, 2009, 05:13 PM
I have a source for at least a few hundred more dead C64s to part out so parts will be around for several more years, even at the rate I'm selling them worldwide. (These are all ugly, abused, beaten, and dead systems from a defunct repair center)

RJ

How much are you selling them for? I could definately use some spare parts supplies. :)

-Andrew

Druid6900
January 9th, 2009, 12:03 PM
I have a source for at least a few hundred more dead C64s to part out so parts will be around for several more years, even at the rate I'm selling them worldwide. (These are all ugly, abused, beaten, and dead systems from a defunct repair center)

RJ

Obviously not a very GOOD repair center LOL

gerrydoire
January 9th, 2009, 12:22 PM
I agree wholeheartedly. I would much prefer to repair than replace!

Sometimes repairing can cost as much as a replacement, especially in this made in china world!

channelmaniac
January 9th, 2009, 12:52 PM
How much are you selling them for? I could definately use some spare parts supplies. :)

-Andrew

I sell the chips on my website. These computers are filthy - stored in trucks, vans, and cars in someone's pasture. The ones that are still decent looking still get parted out and I've offered up some of the keyboards and other parts for the cost of shipping.

I've toyed with the idea of selling repaired boards that have been burn in tested for 24 hours, but it's so cheap to buy something off of eBay.


Obviously not a very GOOD repair center LOL

That's for sure!

rebeltaz
January 10th, 2009, 11:00 PM
OK... well according to what I read on the troubleshooting guide, the problem seems to be a result of 1)the PLA, 2)the kernal ROM or 3)the MPU - blank screen, no border. I don't have a c64 cartridge, so I can't try that test. Where can I find these chips (ChannelManiac?) and how much do they cost? Should I replace them one at a time starting withe the PLA or all at once? BTW - in case it matters, one of the computers has a silver colored C= commodore logo and the other one has a colored C= commodore ===== 64 logo.

Thanks for all of your help.

channelmaniac
January 11th, 2009, 08:33 AM
I have 'em listed up on my website.

RJ

rebeltaz
January 11th, 2009, 09:05 AM
I have 'em listed up on my website.

RJ

Oh... OK... I didn't know you had a web site. You have some great things on your site! I'll have to keep that bookmarked....

Thanks.

channelmaniac
January 11th, 2009, 12:38 PM
Thanks!

If you need something from an old system that isn't chip related, just let me know. I usually have some parts machines sitting around for keyboards, key caps, RF modulators, jacks, etc... Many times that stuff can be had for cost of shipping or enough to buy me lunch plus shipping. ;) It helps to keep those parts out of the land fill.

RJ

rebeltaz
January 11th, 2009, 05:15 PM
So, I do I need to replace all three suspected chips at once or one at a time? I'll order the chips from you tomorrow or Tuesday...

Thanks.

tezza
January 11th, 2009, 05:32 PM
It's unlikely to be all three.

I'd start with what you think is the most likely one. If replacing that doesn't improve matters, replace the next one and see if that works.

It can be hit and miss. In repairing my Vic-20 (http://classic-computers.org.nz/collection/vic-20.htm), I ended up replacing 6 chips. It had a symptom that could have been a number of things. I identified chips that were "possibly" faulty and just started replacing them one at a time. As I replaced the chips, sometimes it would make no difference but at other times things seem to improve. I concluded that when an improvement happened, then that IC must have been bad.

In the end I seemed to have 3 bad chips (the ones in front of the red arrows here (http://www.classic-computers.org.nz/collection/vic20-repair.jpg)). I probably replaced three perfectly good ones, but systematic chip replacement was the only way I could really diagnose/fix this problem.

Tez

channelmaniac
January 11th, 2009, 09:49 PM
Start with the PLA. It's by far the most common source of a problem on the 64.

rebeltaz
January 15th, 2009, 03:08 PM
Ok... I'm sorry, but one more question - I'm ordering the parts now, but I have a question about the Kernal ROM. One of the two systems is a 901227-01, but you (ChannelManiac) only show -02 and -03 on your site. Can I substitute the -02 for the -01 or would that not work?

Thanks...

wiskow
January 15th, 2009, 04:29 PM
This is the information posted on zimmers.net about the various C64 kernals:



kernal.901227-01.bin (http://www.zimmers.net/anonftp/pub/cbm/firmware/computers/c64/kernal.901227-01.bin)
This 8-kilobyte 2364 ROM is the first revision of the Commodore 64 KERNAL. The RS-232 timing table is designed for exactly 1 MHz system clock frequency, although no C64 runs at that clock rate. Unlike later KERNAL revisions, this one does not detect the video system (PAL/NTSC). This KERNAL was probably only used in early North American Commodore 64 units.

kernal.901227-02.bin (http://www.zimmers.net/anonftp/pub/cbm/firmware/computers/c64/kernal.901227-02.bin)
This 8-kilobyte 2364 ROM is the second revision of the Commodore 64 KERNAL. It is the second most widely spread version.

kernal.901227-03.bin (http://www.zimmers.net/anonftp/pub/cbm/firmware/computers/c64/kernal.901227-03.bin)
This 8-kilobyte 2364 ROM is the third and essentially last revision of the Commodore 64 KERNAL. It is the most widely spread version.

kernal.906145-02.bin (http://www.zimmers.net/anonftp/pub/cbm/firmware/computers/c64/kernal.906145-02.bin)
This 8-kilobyte 2364 ROM is from a Japanese release Commodore 64.

You shouldn't have any problem putting an 02 or 03 kernal in a machine that has an 01 kernal in it. In fact, it'll probably improve its usability.