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Would anyone be interested in repairing a PET2001?

A

ABH

New Member
Joined
Jan 1, 2012
Messages
1
Location
Portsmouth, United Kingdom
I bought a working black label 2001 a few years ago. All has been fine but this week I now have a screen full of random characters at power on. After searching through the web I suspect a memory or rom fault.

The unit doesn't have it's original memory chips but has two 2114 Ram Adaptors fitted. Other than that it appears fairly stock and in great condition. i've reseated all the chips on the adaptors and the main motherboard but the fault remains.

Before I embark on a series of trial and error repairs, I wondered if anyone UK based with experience repairing these units would be interested in working on it for me.

Like many owners my machine has great sentimental value and I really would prefer a 'real' engineer to breathe life back into it :)

best
Andrew
 
Andrew, for those interested, it might be useful if you updated your profile to show your location. We do have an international audience and in this case, location matters. So if you're located in Burkina Faso, you'd probably like a fellow countryman to do the repair to keep down shipping costs.

Happy New Year!
 
If I was in the UK, I would definitely be interested.. but unfortunately I'm a bit far removed.
If you decide to look into it further, I would start with checking the reset signal to check if the CPU is running or is being held in a reset condition.
It should be low for a bit over a second, then should go high (5V).
Reset is pin 40 on the 6502.
Wish I was geographically situated to give more direct assistance, but hope this PET finds its way back to life..
 
gubbish said:
Wish I was geographically situated to give more direct assistance, but hope this PET finds its way back to life..
Click to expand...

gubbish,
If it turns out that the OP has a 2001 with impossible to find 6540 ROMs and 6550 RAMs, he would be best off by procurring one of your PETVet boards. Do you have any prototypes available yet?
-Dave
 
Hi Dave,

Yes, I do have a few of the PETVet boards available. I still need to put a serial bootloader on the chip so users can change the ROM images.
Andrew, the PETVet board is a RAM/ROM replacement that I recently built that fits into the 6502 socket on your PET.
It should be useful for debugging PET problems as it bypasses all of the RAM and ROM chips in the computer, which are often bad in old PETs..
I'll post information about how to get one shortly as soon as I get a chance to finish the firmware on it.
 
Hello all,
I,too, have a Pet2001-8. I was working for years but when I pulled it out from storage it now too has the random characters and does not boot. I have the BASIC switch which allowed me to switch between the original and V2 Roms.
I bought the PetDisk from bit fixer hoping to use it but alas, so far the Pet is not working. I took out the Basic switch board and put back the original rooms for now.I also reseated, cleaned contacts but still the same random chars on the screen. I noticed that there are some white stuff on the pcb by the 555 reset area so I am going to try to clean those parts. I would also try to do next to check the reset as mentioned by Gubbish.

If I may, Gubbish, I would like to buy also one of your PetVet kit. I really would like to fix my PET since it has been with me for years... Thanks

btw...being new (although been going here as a guest reader), I thank u all...
 
Ram Chips

Ram Chips

Hi

I Live up the road from you in Portchester. I actually have 17 Commodore Pets of various sorts and have a couple of 2001s. I have repaired quite a few in the past and suggestthat you replace the 2 X 2114 ram chips for starters. If you need a couple then let me know and you can collect them

Colin
 
gubbish said:
Hi Dave,

Yes, I do have a few of the PETVet boards available. I still need to put a serial bootloader on the chip so users can change the ROM images.
Andrew, the PETVet board is a RAM/ROM replacement that I recently built that fits into the 6502 socket on your PET.
It should be useful for debugging PET problems as it bypasses all of the RAM and ROM chips in the computer, which are often bad in old PETs..
Click to expand...
A little OT, but another forum member and I are musing about expanding RAM & ROM in an AIM65 and it occurred to me that the PETVet might actually do the job; how much available RAM and ROM does it provide?
 
sitar said:
I actually have 17 Commodore Pets of various sorts and have a couple of 2001s. I have repaired quite a few in the past and suggestthat you replace the 2 X 2114 ram chips for starters. If you need a couple then let me know and you can collect them
Click to expand...

Hi Colin,
Wow, 17 PETs, that may be a world record.

Andrew states that he get nothing but 'the garbage screen'. That usually implies that the CPU is not running in program. The normal culprits for that symptom are a bad ROM chip or bad low RAM (where system variables and the stack are stored). Although, as you say, both static video RAMs being completely dead might also cause the problem. Usually some of the video RAM locations are working which would allow some of the screen to be cleared.
-Dave
 
Ram Chips

Ram Chips

Hi Dave_m

Yeh, I had a Commodore Pet fettish a few years back and amassed quite a few, sold a few as well. I have had a few Pets where the 2114 ram video ram chips have failed and as they are easily replaced then this is the first thing I try. However, you are right, failing this I then check the clock circuitry. On one occasion I found that the inverter chip around the crystal had failed. Replaced this and it poped straight into life. I also have a number of disk drives ,some of which are the 8 inch versions which are very rare.( I am told I have 2 of the only known 4 in the UK, Not sure if I can believe that). I am now on a Sharp MZ series fettish which I have 7 at the moment, but thinning out a few and hence have one on ebay at the moment.
Note I also have a stock of about 32 6550 ( rare ram chips in case I come across another 2001-8 version)

Colin
 
Hello, I'm the other member that MikeS mentioned trying to expand the AIM-65 memory to include the available language ROMs. Actually I'd like a daughter board whereas the 6502 is unplugged from the main board and plugged back into this one. The daughter board would contain at least 64KBs of RAM/ROM? memory mapped into the proper locations to run the AIM monitor and Language ROMs - BASIC/PL-65/Forth, and lastly Pascal which is why I started this quest...the Pascal interpreter takes up 20KBs mapped into B000 and a 16KB block starting at 4000-7FFF. This cuts the available RAM almost right down the middle...normally it would occupy 0000-7FFF or even then another 8KBs from 8000-9FFF. The A000 block is the AIM65 I/O, the B000-CFFF is the normal language block for the first three 8KB ROM sets, the D000 block is either application or the assembler and the monitor sits at E000-FFFF. I've thought of using a 32KB flash ROM for the upper ROM area abandoning the 8000-9FFF potential RAM mapping and then putting a 32KB SRAM in the lower 0000-7FFF area. Does this sound like something the PETVet could do only in 64KBs of battery backed up SRAM? Seeing that Flash ROMs are fairly large and can be jumper strapped, I've also considered just loading all the language images into various banks and switching them on or off as desired mirroring the monitor block is all four banks...the one that presents the problem is of course the Pascal that drops down into the lower 32KB area. Anyone have any thoughts or interest? Dave Colglazier


gubbish said:
Hi Dave,

Yes, I do have a few of the PETVet boards available. I still need to put a serial bootloader on the chip so users can change the ROM images.
Andrew, the PETVet board is a RAM/ROM replacement that I recently built that fits into the 6502 socket on your PET.
It should be useful for debugging PET problems as it bypasses all of the RAM and ROM chips in the computer, which are often bad in old PETs..
I'll post information about how to get one shortly as soon as I get a chance to finish the firmware on it.
Click to expand...
 
Hi Dave,

It sounds like the PETVet could handle this. It provides 64k of RAM/ROM space, which can be designated as RAM or ROM with a 1k resolution. The ROM contents are stored in the flash memory of an Atmel microcontroller on the board, so upon startup each time the MCU loads the ROM contents and the RAM/ROM mapping. You can have up to 64k of selectable ROM contents, which can be changed with jumpers, and the ROM contents can be reprogrammed via serial port. Also it can halt the 6502 and dump out the memory contents over a serial port for debugging purposes.
I have a few of the PETVet boards, and still need to finish up the serial bootloader, but I will keep you posted about progress on this.
 
Just as a random note, when the PETVet's ready I'll probably want one myself. I had so much fun cooking up harebrained ideas on the "creation thread" for it if nothing else. ;^)
 
Hi gubbish, I probably have found this already but do you have a schematic posted on-line for the PETVet? Thanks, Dave
 
Hi Dave,

I don't have the PETVet schematic up yet but I am hoping to get that and some other PETVet information online today. I'll post a link to it as soon as it's up..
 
RizThomas said:
Hello all,
I,too, have a Pet2001-8. I was working for years but when I pulled it out from storage it now too has the random characters and does not boot. ...
Click to expand...
Sorry, this thread's gone a little OT.

If you haven't solved the problem yet, there are a few simple things you can try while waiting for the Vet to come and fix your PET. Which version is it, i.e. what are the numbers on the ROM and RAM chips?

m
 
Last edited:
Thanks Mike,
I have a PET2001-8 which have 6540ROMS and 6550RAMS. My problems started with garbage (random PETSCII chars) and will not boot.
1. First I did the usual re-seating of the chips. I also have a SMS BASIC switch board where 2 sets of ROM(v1 and V2) are re-located . No Success
2. Reading some tips here, I also checked the reset signals which seems to be ok..pin 40 on CPU goes low then stays high on reset.
3. I noticed that the tape motor keeps on churning so I replace the 6502 cpu.
Now it seems to reset properly. Screen garbage changes and tape motor turns and stops when Reset. However no usual BASIC powerup display. I took out SMS Basic board and transferred the ROMS on original sockets.
4. V1ROMS shows garbage chars but changes on reset. V2ROMS shows BLANK Displays.
5. I have kept RAM to minimal (4Chips) to the right.
All of these with no luck.....so my only hope..it looks like is your PETVet
 
2001 version of my pet-testing ROM

2001 version of my pet-testing ROM

So while we're all eagerly awaiting our PETvets (I know I am)...

RizThomas sent me an IM asking about using the PETtester ROM I wrote some months back in his PET. So in reply I've thrown together a new version of the ROM that ORGs the testing software at F800 instead of F000 so it should be possible to use it in a single 2716 with a suitable adapter. I'm replying to the thread here because I'm probably blind and didn't see how to attach a file to a PM, and, well, it's possible someone might find it useful. (I know someone posted their own more full-featured ROM a while back, however, so "useful" is in the eye of the beholder.)

The new version of the ROM, in addition to ORG-ing at the last 2k boundary, has a substantially improved memory test. It runs two test cycles instead of one, in which the two complementary alternating bit patterns (10101010 and 01010101) are written and read back, instead of the older version's weak single zero-one test. A pass of the odd test is indicated by a lowercase "g". Following a short delay the even test is run and a pass there produces an uppercase "G". Failures are lower and uppercase "B"s respectively. (Come to think of it didn't some really old PETs have reversed-case character generators? If that's the case then reverse appropriately.) Following the RAM test is the display generator/video RAM test. Then wash, rinse, repeat.

I also changed the delay loops so it *should* cause less screen snow on an ancient PET but by consequence it takes less time. It might be on the short side now.

If you wanted to use this version on a 4k-socket (Dynamic) PET you'll have to pad the front of the ROM file by 2k or otherwise burn the contents into the top half of a 2532 or similar. And, as always, it still doesn't work with CRTC models. Whee!
 

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Eudimorphodon said:
...it should be possible to use it in a single 2716 with a suitable adapter...
Click to expand...
... which can be found here:
http://store.go4retro.com/products/ROM%2del-6540.html
It uses an SMT chip, but if you ask him I suspect Jim will assemble one for you; alternatively you can do without the chip if you don't mind adding a couple of jumper wires.

Something to try and check: try it with the two 6520 chips removed, and check/note that the one closest to the ROMs faces in the opposite direction from the rest of the 40-pin chips.
 
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