• Please review our updated Terms and Rules here

Stèphane's and Alex' PET ROM checks

:p Hi to all forum!
Programmer arrived after a month... now i can test & compare eprom with files.
I've have made many try:
- check "old" eprom, find some errors, change faulty eprom ----> black screen
- erase a new set of eprom, burn them, check and put in PET ---> black screen
- try to change 6502 & 6522 with others pulled out from working commodore drive ---> garbage screen or black screen
- try my old mainboard with fresh burned eprom ---> garbage screen (i think old mainboard really faulty)

Now i need your help please ;) ... what can i try for black screen?
Very strange that when i turn on PET, garbage screen apperars one second and after black screen.. seem that basic won't boot. May be one or both 6520 CPU?
 
alex1690 said:
:p Hi to all forum!
Programmer arrived after a month... now i can test & compare eprom with files.
I've have made many try:
- check "old" eprom, find some errors, change faulty eprom ----> black screen
- erase a new set of eprom, burn them, check and put in PET ---> black screen
- try to change 6502 & 6522 with others pulled out from working commodore drive ---> garbage screen or black screen
- try my old mainboard with fresh burned eprom ---> garbage screen (i think old mainboard really faulty)

Now i need your help please ;) ... what can i try for black screen?
Very strange that when i turn on PET, garbage screen apperars one second and after black screen.. seem that basic won't boot. May be one or both 6520 CPU?
Click to expand...
I've (slowly) learned to never take anything for granted; could you please confirm the mainboard model number, the numbers of the image files that you are using/burning and their respective locations for us?

How did you know there were errors in the "old" EPROM and what kind of errors were they?
 
Last edited:
alex1690 said:
Very strange that when i turn on PET, garbage screen apperars one second and after black screen.. seem that basic won't boot. May be one or both 6520 CPU?
Click to expand...

Ciao Alex,
After you installed your new set of EPROMs and PET did not come up properly, did you check the EPROMs again and find any faulty? That would be an indication that something in the PET is damaging your ICs.

Having only a garbage screen is an indication that nothing is running. A garbage screen for a second is normal and then it should blank and then the Commodore message should appear.

So the blank screen is saying that the system is trying to initialize but something is going wrong.

I don't like that when you installed known good CPU and VIA (6522), you got a garbage screen. That is scary. Be very careful not to bend pins during insertion. There is a tool for inserting the larger ICs safely that you might consider buying.

A stubborn PET is discouraging, but with detailed troubleshooting, it can be fixed. Keep detailed notes of all changes being made.
-Dave
 
:(
After many try and eprom erase&burn... no result, PET stuck on black screen.
Please, have you another set of .bin files (Basic V2 or V4) that i can try for my PET 3032?

Thanks!!
 
alex1690 said:
:(
After many try and eprom erase&burn... no result, PET stuck on black screen.
Please, have you another set of .bin files (Basic V2 or V4) that i can try for my PET 3032?

Thanks!!
Click to expand...
Sorry, don't know why no one replied to your last post.

Yes, the order of the EPROMs looks correct.

What type of EPROM are they? They should all be 2532s except D8, the 90447-29 (E000-E7FF), which should be a 2716 (or equivalent); is that what you have? It looks suspiciously like the rest; most 2716s didn't have the little plateau where the window is.
 
MikeS said:
What type of EPROM are they? They should all be 2532s except D8, the 90447-29 (E000-E7FF), which should be a 2716 (or equivalent); is that what you have?
Click to expand...

Mike, that is a good point.

Alex never answered my question about when a new set was installed and produced a blank screen, did he verify the EPROMs were still good to see if the PET was damaging the EPROMs.

Also I'm assuming this machine is a non-CRTC type and will run the screen without initialization by the CPU. Therefore a garbage screen for a second followed by a blank screen means the CPU and EPROMs did run for a while to clear the screen and then went wrong.
 
Also remember even with the last set I sent him, his PET worked OK for a very short while before getting back to garbage, and now just black screen. It is possible the motherboard I sent him could have some fault, although I managed to use it a couple of times in a row without it breaking down.

As a side note, I've got two broken 901465-23 ROM chips here. Both come from Basic V4 machines; first one was Alex' original set and the second one was Frank's set. Maybe it is a coincidence, but in both cases I verified all other ROMs or EPROMs within the set to be OK, just this particular ROM that in both cases caused garbage. They're dated 1981-wk15 (Alex) and 1983-wk08 (Frank). I didn't even know Commodore produced V4 ROM sets as late as February 1983 but maybe these were upgrade sets for the last batch of users. Would the UD5 slot on the 2001N/3000 series motherboard be particularly sensitive to power peaks etc than all the other ROMs and chips are?
 
Hmm,

Anders you'll remember that you sent me a replacement BASIC 2 board for my Pet 3032. We (Philip Avery and I) eventually found the problem on the original board was faulty BASIC 4.0 ROMs . Two seemed to be at fault. The Kernal and the start of BASIC at good old chip 901465-23.

This may or may not contribute evidence to your theory.

Tez
 
:D
Hi to all! Very happy to receive many ideas to restore PET.
Today i made a new try: erase two set of eprom (TMS2532JL & HN462716) and i program first set with BASIC V2 and second set with BASIC V4... :( same blank screen after one second of garbage screen, seem as dave_m say, that PET start inizialize ok but something going wrong.
I test eprom with programmer (GQ4X seem burn eprom ok, verify is ok all times) and compare with images but no errors so PET don't break eprom during startup.

Have you a dump image of your eprom BASIC V2 & V4 please? If you mail me i can try with that.
Many Thanks!
 
alex1690 said:
Have you a dump image of your eprom BASIC V2 & V4 please? If you mail me i can try with that. Many Thanks!
Click to expand...

Alex, If you got the data from the Zimmer website and you are sure it is for your PET configuration, you should be OK. I think we can assume now that the ROMs are OK. It must be something else.

Can you review with us the status of your big chips (40 pin).

Also, what troubleshooting tools do you have? Do you have a "Logic Probe"? It is a gadget that tells you if a signal is high, low or pulsing. The indicator will be lighted, not lighted or blinking.
 
No, i haven't a logic probe :( today i find on ebay two new 6520 cpu.. i try to change that as a new try. After this i post results... hope good ;)
 
alex1690 said:
No, i haven't a logic probe :( today i find on ebay two new 6520 cpu.. i try to change that as a new try. After this i post results... hope good ;)
Click to expand...
Have you tried powering up with both 6520s removed? If you have and it still had the same problem then I'm afraid that you'll probably be disappointed; a bad 6520 can certainly cause problems if it interferes with the address, data or interrupt buses, but AFAIK they are not crucial to the boot process so with both of them removed the PET should still come up with a normal screen (but no keyboard or I/O).

Does anyone reading this have a working 2001-N or 30xx PET with socketed 6520s who could confirm that if you remove both of them the PET still boots to a normal screen? The old 2001 certainly does, and I see no reason why the dynamic RAM version should be any different.
 
Ok, these are my results with a fully working 3000 series PET:

No big chips at all: garbage display
6502 CPU only: Basic prompt, slight flicker but no garbage, no cursor
6522 added: Basic prompt, no flicker but also no cursor
Both 6520s added: Basic prompt, cursor, fully up to duty

I don't know off-hand which 6520 handles what, and I suppose it was not meaningful for me to re-add one chip at a time. Clearly a working / properly powered motherboard should generate garbage or Basic prompt at all cases. Perhaps a really bad 6520 could short something so you get a black screen or just garbage.

As a side note, I tried all four big chips from the second motherboard, the one that was crackling and smoking. It appears all chips are working, although I didn't plug in any IEEE device to be certain the 6522 still is OK. It makes me curious if the RAM on the board will be good too. Eventually I will try to replace those big diodes in the power supply circuit, and maybe it will turn out as one more working PET.
 
I just wanted to confirm that you still have a normal screen (without a cursor) even if all three I/O chips (2x6520 & 6522) are removed.
Thanks for taking the time and trouble.

BTW, the main IEEE interface is actually the 6520 at UC6, not the 6522; AFAIK the PET will work just fne without it except for IEEE I/O.

Good luck with that other board; if even only one diode shorts out you're likely to get crackling and smoking but it's unlikely that it'll cause any damage, so your chances are good; if there were that bad a short anywhere else you probably would have blown up a chip or burnt a trace.

(They make the circuit board traces thin in order to protect the fuse ;-) )
 
Are you sure about 6520 vs 6522? At least I remember at least one of my PET's, can't remember exactly which model, went from no-show IEEE communication to working state after swapping the 6522. In any case, the best scenario of course is to have working chips in all slots.

I wonder about Alex' board, the one I sent him. As I have mentioned before, it could have gotten damaged in transport. If there was a local user with a similar model PET, the motherboard could be put into that transformer/monitor combo to see if it works any different.

We'll see what the results are after pulling all the big chips, if you get a static screen of garbage or if it still goes blank in a second.
 
carlsson said:
Are you sure about 6520 vs 6522? At least I remember at least one of my PET's, can't remember exactly which model, went from no-show IEEE communication to working state after swapping the 6522. In any case, the best scenario of course is to have working chips in all slots.
Click to expand...
Ah, no, I meant that the 6520 at UC6 only handles the IEEE interface, so removing it does not affect anything else; on the other hand, all sorts of things including a bad 6522 could keep the IEEE I/O from working.
 
Yes, the 6522 touches many circuits. It has some of the IEEE 488 handshake signals, the User Port, and the cassette #2 READ signal.

Does it also have the internal counter that creates the jiffy clock interrupt?
 
You must log in or register to reply here.
Back
Top