A little help here guy! " C64 Black screen"

[replayuk]

My c64 now has this black screen, I was told it could be the pla chip, so off I went and bought the super Pla chip & installed it and I still have the black screen.
I`ve checked all the voltages and they all seem ok.

Maybe it could be the vic chip or the timing chip next to the vic chip.

any help to fix the poor c64 would be very much appreciated guys.

Oh sorry for the edit but my c64 board is issue 250425

 

[Bryce]

Hi,
there are several other things that it could be. The first thing I usually check is whether a cartridge works or not (This checks whether the Kernal ROM is broken). It could be the 74LS08 or a RAM problem. It could be the master clock (as you mentioned) or it could be the 7406 (if this is damaged, the floppy drive doesn't reset on startup).

Bryce.

 

[mjnurney]

It could be many things ?... Are the chips in your 64 soldered or socketed ?

I could look at it for you

 

[TheCorfiot]

A cart will only help identify if the Basic Rom is crapped, the Kernal must be working..

As you have replaced the PLA, and kept the old good one too i hope, my money is on the RAM..

If the guys above cant help i would be happy to repair it for you

TC

 

[replayuk]

Sorry to say i give up on this repair, i tried a super pla, the vic chip works fine, cannot test ram as i dont have any ram chips, nor any other chips other than the one`s i just mentioned.
I do have a eprom programmer, if i was to burn new data onto blank chips but i`ve never used it so that would be trial & error if i tried to burn new chips for the c64.

 

[Sardine]

I can recommend tc for the repair.

Give him a pm

 

[replayuk]

Well i fixed the c64 today, it was a ram fault.
I also fitted the super pla to see how it compairs to the original, up too now i can say its faultless, but i`ve not finished testing the super pla as yet.

Thankyou to everyone who posted on this thread giving me idea`s what to look for next.

 

[replayuk]

I thought seeing as you all pointed me i the right directions that it would only be fair to show you all the c64 as it is now after being fixed by all your step by step help on amibay.

[img=http://s12.postimg.org/ivriooqd5/DSC_0014.jpg]

[img=http://s2.postimg.org/5dzbwk6x1/DSC_0015.jpg]

[img=http://s24.postimg.org/qdgfpu2ch/DSC_0007.jpg]

[img=http://s22.postimg.org/fvqudbkyl/DSC_0006.jpg]




As you can see i socketed all the most important chips on the c64 board, and also replaced the ram both banks of 32k top and bottom banks.
I also socketed the cpu, along with the pla and sid, plus the kernal and other chips along the board just incase this ever happens again.
I also checked the voltages accross the board, they all showed the correct voltages.

Thanksyou for all your help in finding the fault to why i had the black screen on my c64.

Hope if anyone else has this problem, then maybe this thread will help repair your c64 too.

By the way i did retro bright my case while i was working on the motherboard of the c64 it came out great, all i used was proxide & bleaching powder to bring the c64 back to how it used too be 30 or so years ago.

 

[UberFreak]

I recently fixed a C64 with such an issue, it was the PLA and one of the ROMs (cant remember which one).
Replacing the bad PLA still gave a black screen, so I "finger checked" the ROMs and one of them was running hot.
Replaced it and all is well, so far.

 

[replayuk]

I wonder why the pla chip cannot be copied onto a standard blank eprom chip without all this super pla thing going on.
I would have thought we could just get the old eprom programmer out then copy the pla chip and re-burn the data onto a blank eprom?

I take it this is not the case with the pla, and if so which chips on the c64 can be copied???

 

[Bryce]

The PLA can be recreated with a normal EPROM, however, the pinout needs to be slightly modified, so it needs a few additional wires to make it work and then looks something like this:

https://mutantcaterpillar.files.wordpress.com/2012/02/eprom_in_situ.jpg

My C64 has been happily running with one of these for several years.

Bryce.

 

[Deleted member 14264]

The PLA can be recreated with a normal EPROM, ...

I have a serious caveat about that.

New EPROMs that are available on the market will cause serious glitches when you use them as PLA substitutes and will cause many cartridges to malfunction.

See http://sleepingelephant.com/ipw-web/bulletin/bb/viewtopic.php?f=5&t=5533

I have myself sold a number of PLA substitutes based on ST's M27C512-90B6 and they worked perfectly but this chip is discontinued since early 2011. Nowadays if you turn to eBay to get this chip what you'll get is actually a rebranded Winbond chip and they too cause massive glitches.

The best cartridge to test if a ROM based PLA sub works fine is Super Zaxxon. I also suggested a test circuit based on a 74LS279.

I still have GENUINE ST M27C512-90B6 which I guarantee will not cause glitches and I sell them for a pityful 3$US each, PROGRAMMED.

You can use the adapter suggested here: http://www.vic20.de/html/eprom_pla_8296_und_c64.html

Or buy one on a PCB sold by Jim Brain here:
http://store.go4retro.com/pladapter/

This is the least expensive solution I know of for PLA substitutes and I only recommend it for boards 250425 and 250466. (added edit: the SX-64 is fine with this solution too)

Or you can buy one of my PLAnkton chips which works on all boards and worry about nothing...

A text by Thomas "Skoe" Giesel (creator of easy flash 3) about this:
http://www.zimmers.net/anonftp/pub/cbm/firmware/computers/c64/C64_PLA_Dissected.pdf

BTW: The photo you posted is a replacement kernal for the VIC-20 - nothing to do with PLA sub

 

[Bryce]

Yes, the photo was just the first random picture that came up when I typed "C64 PLA EPROM" into google, which is why I said it looks "something like this".
I'm not sure what brand EPROM I used, but it's most likely quite an old one as I have a considerable stock of 27C512 (mostly from ST I think) that definitely aren't new. I have heard that there can be problems with the EPROM solution, but I very much doubt that the instability could cause damage to any other part of the C64, so if you have an EPROM and needed a PLA, it would be the fastest cheapest way to get the computer running. If it doesn't work, you can always go back to one of the other solutions.
Unfortunately I don't own Super Zaxxon on cartridge (donations welcome ), but anything else I've tried on the C64 have worked so far.

Bryce.

Edit: Here's a picture that includes both VIC20 EPROM mods
http://www.vic20.de/assets/images/P0001961.jpg

 

[replayuk]

Good god Bryce that doesn't look very nice with all the wires spread about like that does it.

Ok so what about the vic chip can that be copied without all the wires hanging about the epromm chip when copied.

I`m very suprised that someone cant make something so that the pla can be copied straight onto a blank epromm so it can be plugged directly onto the c64 board without any issue`s.

 

[Deleted member 14264]

Yes, the photo was just the first random picture that came up when I typed "C64 PLA EPROM" into google, which is why I said it looks "something like this".

Actually, that was some guy trying to insult me on Lemon64 who posted this to give the idea that my PROM based PLA subs are junk stuff.

I'm not sure what brand EPROM I used, but it's most likely quite an old one as I have a considerable stock of 27C512 (mostly from ST I think) that definitely aren't new. I have heard that there can be problems with the EPROM solution, but I very much doubt that the instability could cause damage to any other part of the C64...

I concur with you there. Groepaz and Jens Schönfeld have been beating the "bus contention" drum ever since I've been selling PLAkate (the predecessor to PLAnkton). (E)PROMs which generate glitches can cause the 64 to malfunction, especially with various cartridges but I have never seen any damage occur as a result.

Edit: Here's a picture that includes both VIC20 EPROM mods
http://www.vic20.de/assets/images/P0001961.jpg

Mine looks more like this:


If you don't have Super Zaxxon, FastLoad may be a form of test and I suggested this circuit to Ray Carlsen:


The button is supposed to turn off the LED - if you have a problematic PLA, it will always switch back on.

I`m very suprised that someone cant make something so that the pla can be copied straight onto a blank epromm so it can be plugged directly onto the c64 board without any issue`s.

As I said above, Jim Brain sells an adapter specifically for that. Its then up to you to ensure you use the right type of (E)PROM. Very fast PROMs such as those from Atmel presently available at Digikey or Mouser will generate a significant amount of glitches but there is a way to filter them.

If you use (E)PROMs that are too slow (more than 120ns usually means too slow) will cause bus access problems. The ideal response speed is usually around 100-90ns AND you must make sure the chip has the right slew rate.

All this combines to make the ST M27C512-90B6 the ideal chip - I have 30 of them left. As I said, don't try to buy them from chinese sellers on eBay; all you'll get are fakes.

Ray Carlsen also has a bunch of the genuine chips in stock.

 

[replayuk]

So what about the vic chip can that be copied?

 

[Deleted member 14264]

So what about the vic chip can that be copied?

The PLA is the only chip of more than 20 pins which can be "copied" or replaced with other things that can perform the same job. All 74LS series chips in the 64 can be safely replaced with 74HCT chips which will last longer since they consume less power.

One exception is the 6581 SID which can be replaced with SwinSID.

 

[Bryce]

Good god Bryce that doesn't look very nice with all the wires spread about like that does it.

Just to be very clear about this... NONE OF THE PICTURES I POSTED IN THIS THREAD WERE MY WORK!!!! Yes, the job looks rather messily done.

Bryce.

 

[Deleted member 14264]

@Bryce
Yeah, obviously since they were originally posted by someone else on another forum.

 

[Bryce]

@Bryce
Yeah, obviously since they were originally posted by someone else on another forum.

Yeah, but you never know. Maybe someone might think I had done them

Bryce.