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DistantStar001

I'm Getting My First C64, And I Have Questions

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So I've been researching PLA replacements and the most affordable option appears to be the "MyTec PLAtinum™ PLA Replacement Module". Overall, the specs look good, with a few bells and whistles that I could live without (I don't think I'll be needing the LED indicators on an internal component). My question is that it's advertised as having "HIRAM & AEC Tap Points", but I'm not sure what they are, or if they're even necessary? I'm not sure I want "loose" wires on my board, but if there's some advantage, maybe someone could let me know.

 

Also, if anyone has a better recommendation for a PLA replacement, I'm all ears.

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So I installed the new PLA (MyTec PLAtinum) and following the instructions to the letter, I had to add a ceramic capacitor to the back of the board to correct some timing issues, but I still get a black screen.

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So I must have done a number to this thing. I finally got a dead test cart (yes I know I should have done that right away, but live and learn). It's marked 781220/586220 and has two modes that can be selected by a small jumper. I was informed that it was compatible with my board (NO.250407 REV.A). I plugged it in and got a black screen on the first mode, and flashing screen on the second. The screen flashes 1 or 6 times, which I understand to correspond to bad RAM chips on the board. I tried piggybacking known good chips on top to no avail. I tried undoing all modification and restoring my old PLA... So far nothing's worked. I know this thing's trying to tell me something, I'm just not sure what.

 

Another oddity here is that 4 of the RAM chips are marked as MK4564N-20, while the other two are marked 4264-2. My understanding is that the c64 is supposed to have 4164 chips (same as the Apple //e). I know that the 4262 chips are compatible with the compatible with the 4162s, but what about the 4562s? Could that be a source of my problems?

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Just got this thing to (sorta) work! The diagnostic shows bad chips in U1, U2, and U18. I believe that works out to the SID, and both CIA's. My original PLA seems to be fine, and I looked up the part # MK4564N-20, and got a clock chip? I'm guessing that since these are MOS chips, that was just Commodore's part #. I managed to piggyback a 4164 from a //e board (Apple-branded and all), and now the ram checks out OK. In any case, at least now I know what I have to replace! And now I'm on my way to some long-awaited Commodore computing! :-)

 

also, does anyone know a good source (or substitute) for a CIA? The SID I think I can find, but the CIA's don't come up that often (at least not from what I've found).

 

Quick update: I just got my Commodore boot screen! But my keyboard is still wonky (though not as wonky as before). I'm guessing I still have to replace those chips if I want it to work properly, but at least it's ALIVE!!!

Edited by DistantStar001

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What continent are you on? I normally dont part with CIAs but I will sell you one at a low price since youve stuck with this C64 instead of recycling it.

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What continent are you on? I normally dont part with CIAs but I will sell you one at a low price since youve stuck with this C64 instead of recycling it.

 

Thank you so much for your offer, but I'm actually not sure I'm going to need it. When I ran the diagnostic cart I didn't realize that I needed a harness on all the ports (also I don't have one), which I believe is why I'm getting faulty readings on my SID and CIA's. As it is the computer starts up normal, with no glitches indicative of a CIA or SID failure. It passes the dead test, with no reports of failed ICs, as well as the sound test on the diagnostic cart. Since the SID and CIA's are responsible for controlling all the various ports, and as it's only the diagnostic cart that reports a problem, my operating hypothesis at the moment is that the ICs are actually fine and that the reported failures are the result of cart not getting a response from the harness.

 

Again thank you for responding, and to answer your question I live in the United States. Should I discover that of my CIA's are bad I will post it in this thread, but as it stands (and since the CIA in U1 and my SID are soldered not socketed) I really don't want to mess with what appears to be a working machine.

 

 

My next steps are to find a proper top shell (as the current one is from a VIC-20 and doesn't hook in the back) and to properly socket the new RAM. Sadly, I was outbid on a 1541 earlier today, but eventually, I'll get one. Until then I'll be hunting for one of my favorite games, Star Trek Strategic Operations Simulator! I gotta test those joystick ports with something. Thanks again. :-)

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Ok, new problem. The black screen is back, but this time there's no power light? Either on the computer or on the dead test cart.

 

It's definitely an issue with the 5v. The VIC and the 7805 get worm when powered, and the screen goes black, but everything else stays cool. Also when I plugged the MyTec PLAtinum into U17 the LED stays dark. I checked the fuse, and it's fine. Any suggestions?

Edited by DistantStar001

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Update: I just looked this up, and found a thread on Lemon64 with the exact same problem. It wasn't as helpful as I hoped since I have a different board. However, I was able to measure the correct voltages from the 7805 and 7812 in V1 and V2, which isn't surprising since I don't think the 9v line is the problem. The responder (mrr19121970) also suggested measuring the voltage at the solder dot between C33 and U17. The problem with that is that there are two on my board. The closer one (on the left) reads between 0.10 and 0.15v, and the one on the right reads between 0.01 and 0.02v. I'm guessing that at least one (if not both) of those is wrong. The bottom line is that mrr19121970 suggested the power switch as the culprit, but since these are different boards, I'd really like to be sure. Also, How do I fix this? If it is the switch, then do I replace it, or would some contact cleaner do the trick?

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I had a similar problem with a C64GS. The power supply was OK, but the computer was only working with +5V -the 9V rail was dry. And I discovered that when you have such scenario, shit happens. I had to replace all the RAM ICs, the SID and even the LED. And the problem was the power switch: it was rusty inside, and was only switching on one power rail.

 

Before I noticed the real failure, I replaced just the RAM, and seemingly got the console working -but had no sound. Test cratrdige produced strange reports, with SID often failing. And the LED was still dark.

 

After passing the test, I switched off the console and it didn't turn on again. Then I noticed the problem with the power switch, I guessed which would be the result of lacking the 9V supply. I cleaned the switch and verified it was working properly, and replaced again the RAM ICs & 8580 -and it was all! The system is now working flawlessly.

 

Good luck with it!

 

EDIT: I didn't read your previous message before writing mine. I had to open the power switch and clean it from inside, using a lápiz de fibras (sorry, don't know the name for it in english), since the metal plates where black & corroded. I guess contact cleaner would have been no help with mine.

Edited by deepfb

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So I removed, dismantled, cleaned, reassembled, tested, and reinstalled the switch. It's not the switch. Any ideas?

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Posted (edited)

Which RAM ICs do you have? Did you replace any of the original 4116 ICs?

  • If you have those 4116 ICs, check the +5v (pin 9), -5v (pin 1) and +12v (pin 8). Ground is on pin 16. I suggest testing voltages on RAM ICs since it is easy to find all of them there. If you have all of them in its place, we may discard a problem on the supply side.
  • If you replaced 4116 ICs, I guess you modified the 4164 ICs to match the pinout of the former ones, isn't it?
Edited by deepfb

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I haven't replaced any of the ICs, only piggybacked the Ram. Also, the power issue seems to be affecting the entire 5v line, as the PLA and cartridge port aren't getting any power.

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Posted (edited)

So I've once again rebuilt my power supply, straightened all the leads on every capacitor on the board (the way they were soldered they sit rather tall from the board and tend to bend with enough length that they could cause shorts), and now I once again have life (of a sort). However, no matter how many RAM chips I piggyback I still have a black screen, and the dead test won't boot. The diagnostic will, and even reported bad chips in U22, U23, U11, and U12 (all RAM chips). However, after repeated boots, it now gives me either a slightly garbled screen, or a good screen and just sits there.

 

From what I can tell, I think it's still a RAM issue, but since piggybacking isn't working anymore, I guess I have to bite the bullet, and socket and replace all the RAM on the board. Unless someone has a better idea?

 

But at least progress... :-\

Edited by DistantStar001
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I would replace all the RAM ICs, yes -but please take into account that 4164 circuit is not a direct replacement for 4116.

 

Also, C64 boards are very fragile, so I would recommend to *cut* the pins of the ICs, then clean the pads, then socket everything. Trying to unsolder the ICs may would end with some "reconstructive surgery" on some tracks :-/

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I would replace all the RAM ICs, yes -but please take into account that 4164 circuit is not a direct replacement for 4116.

From what I can see, there are no 4116 chips. On this board, 6 of the chips are marked 4564, and 2 are marked 4264. I wasn't able to find anything on the 4564s, but I did learn that the 4264s are pin and electrically compatible with the 4164s. From what I understand, most C64s used 4164s (but then, not mine), then again, I know that I'm not the first to have messed with this board. I'm assuming that the 4564s are at least compatible with the 4164s since piggybacking did initially provide good results. Am I missing something?

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Posted (edited)

Well, regardless of what kind of chips they were (4116, 4164, 4264 or 4564) they were definitely garbage. As I cut them out three of them fell to pieces, and four others chipped or cracked.

 

I think I'm on the right track with socketing and replacing them.

Edited by DistantStar001

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Before installing the new ones, I would measure the supply voltage on the socket. If they are just 4164 or compatible, check the +5V pin.

 

If most of them were in a frail condition, I guess a) One of them had a shortcut that fried the others, and/or 2) The power side may not me working properly. Good luck with it! :)

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Posted (edited)

If you haven't already bought RAM chips, this is a pretty good deal on ebay; (not my sale though)

 

https://www.ebay.com/itm/8-KM4164B-15-64Kx1-Dynamic-RAM-DRAM-4164-Commodore-Apple-Oric-ZX-Pravetz/183722288512?hash=item2ac6b3a580:g:~UcAAOSwctJcAyx-

 

Also, a note on that cardboard "heat sink" in your C-64. Many people remove that beast. It traps in heat, and does little else. If you happen to have any chips running really hot, use individual IC heat sinks.

If you need CIA chips in the future, I can spare one or two.

 

.

Edited by motrucker
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Posted (edited)

Update: I removed, and socketed all the Ram, but managed to damage at least 3 traces in the process. I tried patching them with wire, but it didn't help (the best I got was flashing on the dead test, and occasionally gibberish on the diagnostic cart), so I decided to buy two new boards to see if I could use them to figure out what's wrong with my first.

 

The first new board is missing its SID, but boots to the dead test. The color RAM reports bad, which isn't a surprise given the funky colors of the text. Also U9, U21, and U23 report bad, after that it just stops. I tried swapping the VIC since it's the only chip socketed on the board but got the same result.

 

The second new board is socketed on all major chips but was missing its PLA. All I get is a black screen even with a known good PLA installed. There's no flashing on the dead test, and swapping the VIC didn't help. Physically, the board has some problems. A number of the ceramic capacitors have odd white marks on them, and at least one is badly chipped (I think that's a large part of its problems). Also, when I got it, the power switch was bridged to be permanently on. I fixed the switch, and it seems to function normally.

 

All the boards in question are 250407s, with the new ones being REV.B, as opposed to my original, which is REV.A. Any ideas on how I can get any one of these to work?

Edited by DistantStar001

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Posted (edited)

Bad VIC-II may produce errors on colour RAM report, but I undestand that you have tried all the VIC-II ICs you have on the first new board, isn't it?

 

If it is so, I can't decide wich board I would try to repair first, since they both seem quite difficult. I may choose the one that looks cleaner and/or less rusty.

 

Btw, those ceramic capacitors may be decoupling capacitors. Bad decoupling capacitors are a problem when a lot of them are missing or broken; if it is just one or two, all you need is not having a short between its legs. It can be "open" or chipped, whatever, and it may not work, BUT this should not be a critical problem (the IC which it is decoupling will do its job anyway). Good luck!

Edited by deepfb

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So I removed, dismantled, cleaned, reassembled, tested, and reinstalled the switch. It's not the switch. Any ideas?

 

Does the power LED light up? If not, I think that indicates a problem with the switch or power supply rather than a problem with the ICs.

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Posted (edited)

Bad VIC-II may produce errors on colour RAM report, but I undestand that you have tried all the VIC-II ICs you have on the first new board, isn't it?

Yes, I've swapped all three VICs between all three boards. On the first new board, all three booted to the dead test and gave the same result.

 

If it is so, I can't decide wich board I would try to repair first, since they both seem quite difficult. I may choose the one that looks cleaner and/or less rusty.

For the most part, both of the new boards seem to be in equally good physical condition, but new board #2 is missing C-107. The whole board appears to have been recapped, but unlike the other boards, there's nothing in that spot. So maybe that's the problem?

 

 

Btw, those ceramic capacitors may be decoupling capacitors. Bad decoupling capacitors are a problem when a lot of them are missing or broken; if it is just one or two, all you need is not having a short between its legs. It can be "open" or chipped, whatever, and it may not work, BUT this should not be a critical problem (the IC which it is decoupling will do its job anyway). Good luck!

It is literally because of the number of capacitors that show signs of damage that has me wondering. About 12 of them have white marks, and then there's the one with a chip.

Edited by DistantStar001

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Posted (edited)

Can you post pictures for C107 and those ceramic capacitors? And I would consider looking over the recap job previously done -some people make a botch of it when recapping, so you may find capacitors placed the other way, and/or faulty solders.

Edited by deepfb

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Posted (edited)

IMG 1331


You can see some of the white marks in this, but some were bent over on the other side. Also, I removed the chipped one and cleared the holes at C107.

Edited by DistantStar001

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