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Got another PET: CBM 3008, memory problem again?

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Denniske1976

Experienced Member
Joined
Jan 17, 2011
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The Netherlands
Hi all,

Picked up another PET today, a CBM 3008 this time. I think it's got a memory problem. When I switch it on, BASIC 4.0 starts but I get "1022 bytes free". Of course, this is an 8kb machine but isn't there supposed to be around 7kb free?

Also, this one has a plastic case?!? The other 3032 I have is an all metal case and cover. This one is metal with an all plastic cover (the "lid").

Anyone? Can't find too much about the 3008 except they weren't around too long and quickly replaced by the 3016 and 3032.

Thanx and a great Easter to everyone.
 
Well, got it out of the car this morning and had a good look at it. It has some stuff my other (3032) one doesn't have:

Those green "plug ports" at the back with some kind of volume knob above it (on the left side):
CBM3008-01.jpg
What is that? Is it to connect a tape recorder? Because that 3032 didn't have those ports and also the port below it wasn't there (it only had 1 x USER and 1 x IEE-488 PORT).

Serial number, obviously a 2001-8 C (for Cassette?) and "Made in USA":
CBM3008-02.jpg

See, 1022 bytes free:
CBM3008-03.jpg

The inside:
CBM3008-04.jpg
ASSY NO is 320351...

A lot more wiring than the 3032 had... I also noticed that only the cover is plastic, the screen cover is steel again, as is the base. Good thing the RAM chips are socketed, but that might also be where it went wrong maybe. Dunno how good a soldering job the previous owner did. Weird thing is that there's also some soldering leftover at the switch banks, probably to try and get it to 16 or 32K?? Because there's two banks of RAM, isn't the 8K supposed to have just one?

Hmm, now where to go from here? Checking the caps again, like with the other one? This one does boot up nicely, though... "Commodore BASIC 4.0" is in front of me in like 5 seconds :)
 

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Yes, the board seems fully populated with RAM chips which in theory should let it go to 32K. Your problem is a faulty RAM chip. They look as if they are socketed? Go through and swap them out with a known good 4116 IC and see if that helps. Hopefully there are no "home brew" mistakes on the board which are causing the issues.

Tez
 
Could this maybe be causing the problem?

CBM3008-009.jpg

CBM3008-010.jpg

It's the switch blocks... someone's been a bit rude in shorting them. Maybe I should replace them? Or just solder the blocks off and bridge the ones that need to be connected?
 
Oh yeah, does anyone know what this board does?
CBM3008-007.jpg

It's connected to those plugs/dial knob in the back.
CBM3008-008.jpg

It's mounted in below the screen, like here:
CBM3008-011.jpg
CBM3008-012.jpg
 
OK I got this one... I actually "downgraded" it back to 16K (but then again, it's supposed to only have 8K anyway).

I removed the crappy soldering job with the caps of the UJxx RAM and took out the 8 chips, it was (from my point of view) a really badly done job and I wanted it out. I left the sockets in, so maybe I'll get some decent caps and reinstall the other 16K.

It turned out the RAM wasn't bad, I checked pins 1, 8 and 9 and they all had the right voltages... then my eye caught the chip in UD4, they've put in a toolkit ROM in that socket. Removed it, powered up the computer and tada: "15389 bytes free" (with one row of RAM chips installed). So, I don't know what that "toolkit" chip did, but it was using up all the memory or probably causing a short because it's missing pins 12 and 24 (or is it supposed to?).

Now I only have one more problem, the switches also are totally screwed as per the pics two posts above. I really wanna remove them, but maybe this is a "if it ain't broke don't try to fix it"?? But the other real problem is the keyboard. Most keys work, but something like 15 keys won't. Some of those 15 will work after I hit them two or three times harder (and then display 3 times the ] character for example). I took the keyboard out, will clean it tomorrow... maybe I just need to clean it and use some contact spray, looks like it's full of dust and stuff.
 
I bet the extra board is an audio amplifier, the potentiometer is a volume control and the two banana plug sockets are for an external speaker.

If you tell us what the IC is on the extra board, we'll know for sure. I can't really tell from the picture :)

===Jac
 
The 741 is an opamp. So yeah, audio amplifier for sure.

By the way did you look up the postcode on the front? Or is that your address? :)

===Jac
 
jac_goudsmit said:
The 741 is an opamp. So yeah, audio amplifier for sure.

By the way did you look up the postcode on the front? Or is that your address? :)

===Jac
Click to expand...
Audio monitor of the cassette signals by the look of it; maybe interface to use a regular deck? It'd sure be helpful if you said/showed where it's connected...
 
Last edited:
Yep, the postal code is from "Stichting Televisie Drenthe", in Assen. Makes sense since I've picked it up in Assen.

The wiring from that audio ANP board is connected to the cassette ports. You can see the red wire in the picture of the mainboard on the first page. It connected to the first (most left) trace on both the internal and the one on the back. Red wire on the internal port and a black one on the port that's in the back.

I've cleaned the keyboard and most keys are working now. Somehow the Q, A, @ and ! won't work though. Any thoughts on this?
 
OK, keyboard is fixed. I used some contact spray and cleaned the rubber feet under each key with a cloth. Now it works like a charm :)

I'll get some of those caps too and get it back to 32K of memory and I'll clean the outside with some bathroom tile cleaner. Dunno what it's called in English, but it's used to prevent fungi and moist wear on tiles and rubber seals. I cleaned my PS/2 cases with it and it did a great job!! It smells like oven cleaner but less aggressive.

So uhm, you think I can hook up a normal tape deck? Because of the banana plugs?
 
I think in the FAT40 motherboards the speaker was connected to the same output as the cassette interface too (sorry I don't have time right now to check the schematics). It kinda makes sense. :)

By the way, I wouldn't have used contact spray. It may work for a while but it leaves a nasty residue that attracts dust and makes everything sticky in the long run. It's better to take some time to clean the contacts by hand, with some alcohol and a Q-tip, or (if you can reach the contacts well enough) with a pencil eraser.

You can also use Windex (a.k.a. Glassex) and that's what I would use for the outside too.

===Jac
 
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