Eudimorphodon
Veteran Member
Hi, all. It's my first post on the forum... I'll try not to be completely useless here.
This weekend I netted three former educational PETs from a warehouse dump near Berkeley, CA. (I'm fairly confident several members of this board were also there.) I selected three different units, primarily for their good looks. Unfortunately it appears I'm excellent at picking lemons. *sigh*
The first unit is a pretty good looking 2001 with the "calculator keypad". (Internally it seems like it's sort of an oddball as despite having the calculator keyboard it has an "N" motherboard with dynamic RAM, complete with punched-out holes where Commodore murdered the second bank of RAM socket pads.) The monitor lights up but there's moving garbage on the screen, IE, the screen is about half-filled with the "normal" character hash but there are stray dots running around within the characters. I picked this one up for a friend so I haven't fooled with it any further.
Second unit is a non-CRTC 9" 4032. It cleaned up very nicely but it's also DOA, this time with non-moving garbage on the screen. This is the one I had the most hope for and done the most with, but as of yet I've had no luck changing its behavior at all. So far I've tried some minor spot-cleaning of the circuit board (not a complete wash, but I tried to get some of the oxidation off the edge connectors and wiped some "gooey" looking dust blobs off of places where I thought it's possible they might be shorting something), and I've also pulled and reseated all socketed chips. It seems from reading the forums that magically works a fair amount of the time. No love here.
Last unit is an 8032, I don't know enough about them to say which motherboard. When powered on this unit makes the "Chripchirpchirp" noise but the screen never lights up. I've tried blind-typing "print chr$(7)" in an attempt to get another chirp with no luck, and another experiment (see #3 below) has me pretty convinced it's not getting to the BASIC prompt.
Anyway, I'd *really* like to get either the 4032 or 8032 working, preferably the 4032. Unfortunately my practical electronics experience is weak and the only tool I have on hand is an auto-ranging DVM, so... here follows the stupid newbie questions.
1: My first inclination is to concentrate on the 4032. Is there a good link out there describing where good test points are for doing basic tests like verifying voltages are on the board?
2: I've been kicking myself for not getting two identical units in order to have greater leeway for swapping parts. That said, given what I had at hand would there be any suggested recipe for swapping socketed chips between units in hopes that something that's bad one place is good another? Is any one chip more likely than any other to go bad? I'm guessing that the 6502, 6520, and 6522s should be freely swappable from one to the other, but ROMs are a bigger problem. Would it be worth trying the 2001's ROMs in the 4032, or should I try the other chips first? (And I don't think I want to swap anything without at least verifying voltages.)
3: Are monitors compatible between 9" and 12" PETs? After hearing the 8032 chirp so cheerfully but have the screen remain dark I stupidly risked putting the unit close enough to one of the 9" units for me to plug the video cable from the 9" into the 8032's motherboard. (Of course both units were powered on to supply the high-voltage lines) When I did that all I saw on the 9" screen was a dim pattern of free-scanning lines. Then I tried reversing it and plugging the 12" screen into the 9" PET's motherboard to see if I'd at least see garbage on it. But it stayed pitch black. When I restored everything back to normal nothing seemed worse for the wear. (Easy enough condition to be in when you're already broken, I guess.)
My conclusion based on those experiments was that the 8032 motherboard isn't outputting a video signal *and* its monitor is dead, but of course those conclusions could be wrong if the monitors are not compatible. Anyone swapped screens between a 9" and 12" before?
4: Does the fact that the 8032 go "chirpchirpchirp" at least suggest the CPU is good?
Anyway, it's a bit frustrating to have struck out so badly. I ended up with three sexy disk drive units along with the PETs, I'd love to be banging my head on trying to get one of *them* to work. Any pointers for getting further on fixing one of these things would be awesome.
Alternatively if someone would be interested in swapping me a working PET 4032 for a sick 8032 and an untested 2040 or 8050 (your choice!) I'd totally be willing to talk trades. Thanks.
This weekend I netted three former educational PETs from a warehouse dump near Berkeley, CA. (I'm fairly confident several members of this board were also there.) I selected three different units, primarily for their good looks. Unfortunately it appears I'm excellent at picking lemons. *sigh*
The first unit is a pretty good looking 2001 with the "calculator keypad". (Internally it seems like it's sort of an oddball as despite having the calculator keyboard it has an "N" motherboard with dynamic RAM, complete with punched-out holes where Commodore murdered the second bank of RAM socket pads.) The monitor lights up but there's moving garbage on the screen, IE, the screen is about half-filled with the "normal" character hash but there are stray dots running around within the characters. I picked this one up for a friend so I haven't fooled with it any further.
Second unit is a non-CRTC 9" 4032. It cleaned up very nicely but it's also DOA, this time with non-moving garbage on the screen. This is the one I had the most hope for and done the most with, but as of yet I've had no luck changing its behavior at all. So far I've tried some minor spot-cleaning of the circuit board (not a complete wash, but I tried to get some of the oxidation off the edge connectors and wiped some "gooey" looking dust blobs off of places where I thought it's possible they might be shorting something), and I've also pulled and reseated all socketed chips. It seems from reading the forums that magically works a fair amount of the time. No love here.
Last unit is an 8032, I don't know enough about them to say which motherboard. When powered on this unit makes the "Chripchirpchirp" noise but the screen never lights up. I've tried blind-typing "print chr$(7)" in an attempt to get another chirp with no luck, and another experiment (see #3 below) has me pretty convinced it's not getting to the BASIC prompt.
Anyway, I'd *really* like to get either the 4032 or 8032 working, preferably the 4032. Unfortunately my practical electronics experience is weak and the only tool I have on hand is an auto-ranging DVM, so... here follows the stupid newbie questions.
1: My first inclination is to concentrate on the 4032. Is there a good link out there describing where good test points are for doing basic tests like verifying voltages are on the board?
2: I've been kicking myself for not getting two identical units in order to have greater leeway for swapping parts. That said, given what I had at hand would there be any suggested recipe for swapping socketed chips between units in hopes that something that's bad one place is good another? Is any one chip more likely than any other to go bad? I'm guessing that the 6502, 6520, and 6522s should be freely swappable from one to the other, but ROMs are a bigger problem. Would it be worth trying the 2001's ROMs in the 4032, or should I try the other chips first? (And I don't think I want to swap anything without at least verifying voltages.)
3: Are monitors compatible between 9" and 12" PETs? After hearing the 8032 chirp so cheerfully but have the screen remain dark I stupidly risked putting the unit close enough to one of the 9" units for me to plug the video cable from the 9" into the 8032's motherboard. (Of course both units were powered on to supply the high-voltage lines) When I did that all I saw on the 9" screen was a dim pattern of free-scanning lines. Then I tried reversing it and plugging the 12" screen into the 9" PET's motherboard to see if I'd at least see garbage on it. But it stayed pitch black. When I restored everything back to normal nothing seemed worse for the wear. (Easy enough condition to be in when you're already broken, I guess.)
My conclusion based on those experiments was that the 8032 motherboard isn't outputting a video signal *and* its monitor is dead, but of course those conclusions could be wrong if the monitors are not compatible. Anyone swapped screens between a 9" and 12" before?
4: Does the fact that the 8032 go "chirpchirpchirp" at least suggest the CPU is good?
Anyway, it's a bit frustrating to have struck out so badly. I ended up with three sexy disk drive units along with the PETs, I'd love to be banging my head on trying to get one of *them* to work. Any pointers for getting further on fixing one of these things would be awesome.
Alternatively if someone would be interested in swapping me a working PET 4032 for a sick 8032 and an untested 2040 or 8050 (your choice!) I'd totally be willing to talk trades. Thanks.
On the bright side you're right there should be a number of folks who may be in driving distance who might be able to help or swap parts. Most any numbered chips will be compatible between the units (6502s can be freely swapped between different systems). You've probably found your way to a few of the recommended sites via google-fu but here's one start on 
