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CBM 3032 no image but seems to power on

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Denniske1976

Experienced Member
Joined
Jan 17, 2011
Messages
480
Location
The Netherlands
Hi all,

I've just gotten hold of a PET (CBM 3032) from someone about 30 minutes ago :) Looks really cool and it seems to be a very early one. Most chips have 1977 date code on them. Still have to go about and clean it, but I thought "Let's power it on and see what happens". Well, I can see the CRT glowing trough the back of the monitor vent and I can hear the current/power but I get no screen. I'm not too familiar with these things but there's supposed to come something like "BASIC Ready" and stuff (like a Commodore 64 right?) up on screen?

Weird thing is when I switch it off and on again I can actually see an image on screen for about 1/10th of a second. It's the whole screen filled with ASCII chararcters from top to bottom and left to right... so I know the screen ain't dead. Could this be some chip that's not good? One of the BASIC chips maybe? Because when I opened up the case (very cool, like the hood of a car LOL) there's like about 12 or maybe even more different BASIC chips stuck on some foam. I'll get some pictures tomorrow and post them up here anyways.

Also: were these things also available as a KIT??!! Because from what I've seen online, mine looks nothing like the other PETs. Well, of course the case is the same but the face plate of mine is silver, with the owner's name on it so it looks as if he made that himeself. Also there's a KEY at the right in the face plate (key-lock??). Don't see that on any of the PETs I've seen online. Keyboard is the same though. It also has a serial number but there's no COMMODORE sticker or label or anything to find on and in the whole machine (not even on the mainboard). That's really weird AFAIC but maybe that was common back then? It does have cassette port, IEE-488 or something? and one very wide connector (also have cables for that so don't know what goes on it but the cables were included).

Anyhoo, the owner told me he put it in storage about 25 years ago and it was working and it's been up in the attick ever since... I checked for loose chips and they all seem to be fine. Just don't know how to check for bad chips ;-)

HELP!?!?! Would really like to get this up and running... I'm more of an "8088/8086 guy" but I always loved PETs for their appearance and I understand they were quite the thing back in the 70ies.

Thanx for reading and have a good one!

Dennis
 
Cool find :) Well first you're right, the easiest thing and first thing to do is reseat the chips, make sure the pins aren't bent, etc. The set of roms that you found inside may indicate that the owner was playing around with upgrades or custom BIOS code so that may be something to check next in the event that the system is filling the screen, cpu blanks that out and jumps to the instructions found for the basic rom.

Could still be a few issues at hand. Keep a note of anything that does change after reseating things.
 
Well, below some chips (on the foam) there was a loose label... guess it was on the system board, looked like one of those that were on older IBM boards as well. That one only says:

GRUPPE: 680
REF: 666

That's all I can find inside or outside of the computer :confused:

I also tried booting it with a key in that key-lock, but to no avail... I have about 30 of the same keys (really long old fasion "front house door keys"). You can't turn the key-lock btw (like with the old 286/386 computers), you can just stick a key in it and leave it in.
 
Are you sure, you've got a CBM inside that CBM case? Each CBM motherboard has an ASSY NO. in copper like this: ASSY-8032110.JPG (picture)

Could you provide some photos taken from the inside to see what board you've got?
 
Yeah I found one: assy no 320351 and Copyright Commodore International. It was in REALLY small code on the system board. Like as in 2 or 3mm high characters ;-) And indeed in copper. Tomorrow I'll try some other BASIC chips. Maybe one of those is faulty. I'll try reseating as well.

Dennis
 
Regarding the key lock can you tell what the wires go to and which scenario goes where? If the key doesn't turn I'm pretty sure it isn't right. I doubt the lock would just rely on continuity from the key heh. You could try shorting certain scenarios with other wire or a paperclip if you're really thinking that's the case although I would kinda think that may just be inline with the power not the ROM.
 
Denniske1976 said:
Weird thing is when I switch it off and on again I can actually see an image on screen for about 1/10th of a second. It's the whole screen filled with ASCII chararcters from top to bottom and left to right...
Click to expand...

That is normal. The video RAM powers up with a random pattern. When the program starts, it clears the video RAM by writing 1000 space characters ($20) to the 25 lines of 40 characters each, then the program should display the standard ***Commodore*** message but apparently the machine is going wrong at that point. It may be an indication bad or incorrect ROM chips installed.



there's like about 12 or maybe even more different BASIC chips stuck on some foam. I'll get some pictures tomorrow and post them up here anyways.
Click to expand...

Yes, good idea to take photos. One of the photos should be a closeup of the row of 24 pin ROM chips so we can check the dash numbers.



Also there's a KEY at the right in the face plate (key-lock??)... and one very wide connector (also have cables for that so don't know what goes on it but the cables were included).
Click to expand...

This must be a custom modification somebody made. If it was a key lock, it seems to have been bypassed as the unit powers up. Perhaps it was used to enable some external hardware. The big connector is for a custom expansion so the PET may have been hooked up to special hardware and perhaps used special software.
 
Well, back again with an update and photos:

So uhm, I had a good look inside the computer:
CBM3032-001small.jpg

And it looks like those BASIC chips were homemade or something. They're really weird piggyback chips or something like that... never seen anything like them:
CBM3032-003small.jpg

As the computer did nothing and there was a full set of chips inside on foam, labelled BASIC 4.0 9000, A000, B000 etc (up to E000), I changed the weird chips with the ones that were on the foam (of course, every chip is were it was... so A000 is were the old A000 was etc):
CBM3032-005small.jpg

So then it looked like this:
CBM3032-004small.jpg

And when I power up the computer I get this screen (and yeah, that's American Dad! in the background... not embarrassed to admit that LOL):
CBM3032-006small.jpg

That's the screen that would flash by every time I cycled power with the other chips. Now it just stays there on the display. Even if I leave it for 20 minutes. So there could still be something wrong. Maybe the chips are in backwards? So 9000 is actually where E0000 should be? I have no way of telling what BASIC ROM goes in what Uxx socket.
 
Kevin,

If the ROMS are BASIC 4 then F000 goes in U9. E000 in U8, D000 in U7, C000 in U6 and B000 in U5. Remove the other chips in U4 and U3. They will be optional ROMS and are not needed for normal operations.

Make sure you have them oriented the right way.

Be careful removing and reinserting the chips. Pet sockets are notorious for suffering damage during this process.

Tez
 
Well, did that and makes no difference :-( Chips are also oriented the right way...

Oh BTW: I'm not Kevin... I'm Dennis ;-) My twin brother is called KeLvin though (Kevin is a persona from the movie TRON hehe) :)
 
I suspect one or more of the original ROMS (seen on the foam) became faulty and the previous owner burnt a whole new set of BASIC EPROMS for the beast. Along with a couple of toolkit ROMS at A000 and 9000.

One of those EPROMS may have developed a fault, a socket could be faulty or it could be something else entirely. Check for bent pins. That happens so easily.

Here is a list I found on the NET of the original ROM chip numbers and which part of ROM they contain. This might be useful if you want to try any of those original ROMS. Hopefully it's accurate.

BASIC 4.0:

901465-19 2332 ROM Basic 4.0 B000-BFFF
901465-23 2332-120 ROM Basic 4.0r B000-BFFF
901465-20 2332-059 ROM Basic 4.0 C000-CFFF
901465-21 2332-096 ROM Basic 4.0 D000-DFFF
901447-29 2316-034 ROM Basic 4.0 E000-E7FF (PET)
901474-02 2316-035 ROM Basic 4.0 E000-E7FF (CBM)
901474-03 2316-041 ROM Basic 4.0 E000-E7FF (CBM 60Hz)
901474-04 2316-059 ROM Basic 4.0 E000-E7FF (CBM 50Hz)
901498-01 2316 ROM Basic 4.0 E000-E7FF (PET 50Hz)
901499-01 2316 ROM Basic 4.0 E000-E7FF (PET 60Hz)
970150-07 2516 EPROM Basic 4.0 E000-E7FF (PET 9" 60Hz)
901465-22 2332-075 ROM Basic 4.0 F000-FFFF

Tez
 
Looking at the closeup of one of the strange "high rise" chips it appears they're 2732 EPROMS. Those are not directly compatible with the PET's sockets, so I suspect the thing underneath them is some sort of homebrew pinout adapter.

I see from the pictures you have quite a few of the original mask ROMs. (The black plastic ones with no paper labels on them.) I'd probably suggest you take stock of all those and see if you might have a complete unaltered set. It appears to me based on the labels that what was in the machine when you opened it up was most of a BASIC 2.0 set (the three black ROMs), but your EDIT ROM, E000, which goes into the second socket from the left, is an EPROM along with the three homemade option ROMs in the last three sockets. Here is a URL:

http://www.zimmers.net/anonftp/pub/cbm/firmware/computers/pet/index.html

listing downloads for most known PET firmware versions. Notice that part of each filename is a part number. It seems like from one of the pictures you have at least four original mask ROMs, see if they add up to a complete BASIC 2.0 set. (I can't read all the model numbers in the photo.) I'm wondering if it's remotely possible that the EPROM in place of the EDIT ROM is customized to call one of those extension ROMs and either it or said extension is bad.

(The keyboard interrupt service routine is in the EDIT ROM, if you were making some sort of integrated customization to the PET firmware replacing the EDIT ROM would be the most straightforward way to link it in at powerup without user intervention.)

If you had an EPROM burner I'd suggest burning a tester ROM to check out the CPU and RAM, but it looks to me like your PET is most of the way to working. It could be something as simple as a bad socket or cracked trace in ROM area. The other alternative is it might be bad RAM. A completely bad zero or one page could cause the system to crash early in the BASIC initialization process.
 
Denniske1976 said:
And it looks like those BASIC chips were homemade or something. They're really weird piggyback chips or something like that... never seen anything like them:
Click to expand...
Well, the Tektronix chips are presumably a custom modified version of BASIC 4; the rest are BASIC2 with a custom E000 ROM and the optional ExBASIC and Toolkit ROMs in 9000-B000, with 2332<>2732 adapters where required. An interesting system to be sure.

Maybe the chips are in backwards? So 9000 is actually where E0000 should be? I have no way of telling what BASIC ROM goes in what Uxx socket.
Click to expand...
Actually, if you took the trouble to look at the schematic page that Nils pointed you to you would find the board layout telling you what goes where. But they're correct: UD3 to UD9 are mapped as 9000 to F000 respectively. Looks like something else is wrong, unless the E000 ROM is looking for something that's not there.

Forget the Tek ROMs for now and only put in the ROMS for C000 to E000 (i.e. the three original ROMs, the E000 EPROM, and leave out 9000, A000 and B000). What is the chip number on the E000 EPROM?
 
Well, I had a look at the "parts and jumpers layout" schematic, 320351-5.gif yesterday but there wasn't too much to see for me. This thing was made when I was 2 years old, you know. Also those other ROM chips seem to have the same numbers on them, they all look the same. I did try the Tek chips B000 - F000 and no avail.

Weird thing is that reset doesn't seem to work either. There's two buttons saying reset do I assume you need to press both to reset? Or does this thing only reset the registers and not power cycle the system.

As you can see I'm not too familiar with this machine. Oldest for me was the Amiga 500 and Philips P2000-T my uncle had (with some cool BASIC game where you walk around a castle with snakes and vampires on a micro cassette, in ASCII mode of course).
 
:) Great to learn! You get to be an old school tech now heh, afterwards you can play Castle Adventures or Rogue, etc
 
OK, I have two ROM chips: 901465 01 and 901465 02. The other two MOS chips are 901465 03 and 901465 24, which I can't identify. Can I get by with just the two BASIC 2 ROM chips?
 
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