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Commodore Pet Troubles

J

jshtulman1

New Member
Joined
Mar 4, 2013
Messages
4
Hey all,

I recently purchased a Commodore Pet computer at a flea market, striking an extremely good deal. Unfortunately, when I came home and plugged it in, the screen was garbled and half the keys don't work. The Pet itself is the one with a "business" keyboard and 32k of RAM. It says CBM on the front instead of PET, if that helps. I appreciate any advice towards fixing this piece of computing history. However, I know nothing of vintage computers and the way they work, so each step will have to be explained in great detail. Thanks in advance for the help! Here are some pictures:
124.jpg122.jpg

The first one, with the screen filled up with letters, only appears for a second after power up; sometimes, it doesn't appear at all.
Usually, it boots to the screen with the messed up letters at the top. I assume it's attempting to say "Commodore Basic". Maybe memory issues?

Once again, thanks for the help!

Sincerely,
Jacob Shtulman
 
Could be a bad character rom. Try re-seating the roms. Are the correct characters shown when you type on the keyboard?
 
Yes, the correct characters show up when typed. However the characters around them start to change into different characters for some odd reason. For example, I'll type "load". LOA comes out fine, then I type in D and it becomes something like "ADAD". Also, when I type in a single character, the computer usually adds a punctuation. When I type, let's say.....C, it'll show up as "C#,".
 
Also, what is the best way to take out the chips? I've tried pulling them off with tweezers, being very careful not to bend any of the contacts, but they seem to be stuck.
 
Maybe Video ram also.
As for removing the chips, I use a small flat blade screwdriver to gently ease up each side and then pushing them back into the sockets,
you don't need to fully remove the chips, what you are trying to do is clear the oxidation from the pins/sockets.

Later,
dabone
 
I've fixed 3 PETs now, which makes me a self-proclaimed expert. :rolleyes: Certainly re-seating the socketed chips is always a good idea, but I think it's going to end up being video RAM or system RAM. Those chips are unfortunately not socketed, so you'll need someone with soldering skills to replace those.
 
I concur with others. I'd start by replacing (or initially reseating if socketed) the video RAM.

The "garbage screen" for a second or so when you first switch on is normal. You don't need to worry about it unless it there permanently.

Tez
 
Reseating didn't do anything, sadly. Now it looks like I will have to replace the video memory. Forgive my ignorance, but where is the video and system memory located? What are the names of the chips and where could I possibly obtain them? Keep in mind it is the revised motherboard from '79. I have a friend who's handy with a soldering iron, so that's not a problem. Thanks for the great advice, though! I can't wait to get this PET up and running.
 
If your board is the same as mine (CBM 3032), then the 2114 video RAM chips are as marked. The image is from a repair article so ignore the other labels.

Tez

2011-07-14-all-board-fixes.jpg
 
Pet Rescue said:
Jshtulman1



There are 8 2114's inside an old Vic 20 if you have a broken one lying around for the video memory.

There are 4116's in an old sinclair spectrum for the system memory.

If it's the dynamic board here's a link to locations.

http://www.dansretropod.com/commodore/pet-cbm-4032.aspx
Click to expand...
I think Tez guessed correctly that out of the ten or so different PET/CBM boards the OP has the 'dynamic RAM' 2001N/3032; all except two use 2114 video RAM chips but it might help if the OP confirmed the part number of the circuit board or at least the model number of the PET.

Note that the one in the above link is actually the Fat40 CRTC 'universal' board, not what's usually referred to as the 'dynamic' board (although it does indeed use dynamic memory).

Some places to buy 2114s:
$2.50: http://www.bigdaddy-enterprises.com/
$1.99: http://www.arcadecomponents.com/memory.html

Speed is not critical but if there is a number like 2114-3 on the end, the lower the better; an L in the suffix means it uses low(er) power.
 
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Hi MikeS

Your spot on that's the universal board in the link, I always get those two mixed up!(Universal meaning can be 40 or 80).

I should remember the dynamic doesn't have a piezo speaker! (I block it out due to my failed 3032 repair attempt :D)
 
Pet Rescue said:
Hi MikeS

Your spot on that's the universal board in the link, I always get those two mixed up!(Universal meaning can be 40 or 80).

I should remember the dynamic doesn't have a piezo speaker! (I block it out due to my failed 3032 repair attempt :D)
Click to expand...
The most obvious clue aside from the beeper is that the old pre-CRTC/beeper PETs have the chips arranged left to right; the old static RAM versions have both RAM and ROM near the front of the board whereas the 'dynamic' boards have RAM across the front and the ROMS near the rear.

The later 80 column and Fat40 versions have the chips arranged front to back, RAM along the left beside the heat sink and the ROMs more or less down the middle.

So, what happened with your 3032?
 
MikeS

So, what happened with your 3032?
Click to expand...

Mike it was painful, every time I found a problem chip another would surface!
I cut my losses and sold her on but I have a nagging suspicion it was a bad socket,
in another repair I had similar faults that were down to a faulty 6502 socket (my chicklet repair).
But it's always there nagging as I will never know what it was.

I don't normally give up but that time I did!

I did later fixed my chiclet pet that has a dynamic board and finally slayed my 3032 demon!
 
Pet Rescue said:
MikeS

Mike it was painful, every time I found a problem chip another would surface!
I cut my losses and sold her on but I have a nagging suspicion it was a bad socket,
in another repair I had similar faults that were down to a faulty 6502 socket (my chicklet repair).
But it's always there nagging as I will never know what it was.

I don't normally give up but that time I did!
Click to expand...
No problem; sometimes mental health trumps the satisfaction of a successful PET repair ;-) I once got so stressed and frustrated working on a particular computer that a friend who was there at the time considered taking me to the local hospital emergency department; fortunately driving around a little on the way and a little time out and I was back to my ever-patient polite and sweet-natured persona that you've gotten to know on this forum ;-)

I did later fixed my chiclet pet that has a dynamic board and finally slayed my 3032 demon!
Click to expand...
Ah yes, I remember that one; still curious whether any dynamic boards with the old keyboard actually ever left the factory or if someone had replaced either one.

I upgraded my chiclet PET's keyboard, upper case half, CRT and stickers way back when as soon as the new keyboard kit became available but of course I still have the old stuff; if I wanted to I guess I could use it to make a new style PET look like the old one and maybe make it worth more to an unsuspecting buyer...
 
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Pet Rescue said:
I don't normally give up but that time I did!
Click to expand...
Yes, that reminds me of my attempted Lisa ProFile repair. Nights and nights of checking, testing, pouring over circuit diagrams and head scratching. In the end I just had to let it go...

Now every time I look at it I feel like it's mocking me (naa...just kidding :) )

Sometimes you just reach the point when enough is enough. If you've given it your best shot then that's all you can do.

Tez
 
Thanks for the empathy guys!

I must say the support you get on this forum is excellent!
Not just the technical help but the moral support too.

Whenever I get stuck it's the first place I head for.
 
MikeS said:
I think Tez guessed correctly that out of the ten or so different PET/CBM boards the OP has the 'dynamic RAM' 2001N/3032; all except two use 2114 video RAM chips...
Click to expand...
Out of interest, which ones don't? Guessing the 8[0/2]96 and SuperPET?

MikeS said:
Some places to buy 2114s:
$2.50: http://www.bigdaddy-enterprises.com/
$1.99: http://www.arcadecomponents.com/memory.html
Click to expand...
Just to add, there is regularly NOS 2114's to be found on evilBay for < £1 each.

Rob
 
crock said:
Out of interest, which ones don't? Guessing the 8[0/2]96 and SuperPET?
Click to expand...
I think you're right (although the early SuperPET may still have used 2114s) and AFAIK all the later B and P models also just used the main RAM for video, but I was thinking of the PETs that had separate video RAM and the two versions of the original 2001 that used 6550s.
 
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two versions of the original 2001 that used 6550s.
Click to expand...

This was the first kind of pet that I got, and it had bad ram, those chips are HARD to find.
(But I now have spare, because when I installed the ram/rom board, I removed all the ram and roms from the mother board.)

Later,
dabone
 
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