PET got seriously ill...

[dave_m]

letter page 2

letter page 2

Here is the letter:

 

[MikeS]

Thank you!

But you're treading on thin ice there; I see that even a post in the "completely off-topic rants" section was criticized for not being about vintage computers (among other things) so a sauerkraut recipe in the Commodore section is really asking for it... ;-)

But my mouth is watering just reading it, despite the "farting Santa Claus" reference ;-)

 

[track18]

Hi there,

But you're treading on thin ice there; I see that even a post in the "completely off-topic rants" section was criticized for not being about vintage computers (among other things) so a sauerkraut recipe in the Commodore section is really asking for it... ;-)

being back from holiday, recovered from swine flu (or something similar) and with kids not too demanding at the very moment, I thought I'd bring this thread back on track by mentioning that meanwhile I've bought some conductive paint, but don't know when I'll find the time to apply it to the PET's keys.

As for building an EPROMmer, I recently read an article about an inexpensive and easy-to-programm microcontroller board called Arduino (http://arduino.cc/) in the German c't magazine. I wonder if this was a suitable device for controlling the burning process, or if there are even Arduino-based EPROMmer designs already out there.

Finally I am glad to hear the sauerkraut parcel made its way to the US -- wasn't sure whether the FDA would allow importing all the kinds of food it contained... BTW, I hereby grant permission to publish my private letter to Dave on the internet ;-) I must, hoever, add an erratum: Haribo's founder's name was *Hans*, not Harald Riegel.

All the best --

 

[dave_m]

As for building an EPROMmer, I recently read an article about an inexpensive and easy-to-programm microcontroller board called Arduino (http://arduino.cc/) in the German c't magazine. I wonder if this was a suitable device for controlling the burning process, or if there are even Arduino-based EPROMmer designs already out there.

Hi track18,

I don't see a lot of programmable I/O pins on the Arduino. At least for the older EPROMs you will need to control all the address and data lines as well as chip select to the device to be programmed. You will also have to have a programming voltage source of 25V for very old parts like the 2532 or 21V for parts like the 2764A, or 12.5V for CMOS types.

Here is a link to a board with a lot of I/O:
Teensy

Here is a link to a data sheet for the old 2532 to see how to program it. It needs a precision 50 milliSecond pulse on the chip select for each address to be programmed.

TMS2532.pdf

 

[dave_m]

BTW, I hereby grant permission to publish my private letter to Dave on the internet ;-) I must, hoever, add an erratum: Haribo's founder's name was *Hans*, not Harald Riegel.

Sorry, you are quite right. I did not request permission to post the letter. I have edited the location. I hope this is not a secret family recipe.

 

[x3r13x1z]

When I bought my Commodore PET 3032 on an auction, I had the same problem with the screen output (garbage characters filled the screen). I didn't know what to do, but I tried to pull out every single IC out of their sockets, and then put them back again. I swiched on the computer, and voila! It's now working! Try, it may solve your problem.

 

[dave_m]

Track's problems involved a bad ROM and other things, but yes, re-seating the socketed chips is a very good thing to start with. It wipes the oxide layer off the pins and allows for good connections.

 

[MikeS]

I've got an 8K 2001 that consistently powers up saying 'HOUT GOSUB' (presumably the tail end of the error message). Replaced all the socketed chips with known good ones, no change, so I put it aside for a rainy day.

But this thread has inspired me to have another look one of these fine days; meanwhile, anybody got any good ideas how to proceed? It looks like someone's already replaced a number of chips, but they look pretty good.

Probably time to build a logic analyzer...

 

[dave_m]

This is a tricky one. You might try to power up with ground on pin 5 of the user port. This should get to the monitor. If so, check for the contents of RAM using the .M command (.M 1000 1020), and see it you can edit memory with FFFF and 0000 patterns and see if there are stuck bits.

 

[MikeS]

This is a tricky one. You might try to power up with ground on pin 5 of the user port. This should get to the monitor. If so, check for the contents of RAM using the .M command (.M 1000 1020), and see it you can edit memory with FFFF and 0000 patterns and see if there are stuck bits.

Ah, forgot to mention that it's unresponsive. But even if it weren't, it's got BASIC 1 ROMs, so no monitor. The chips are OK, so if it's that kind of problem it'd have to be the buffers (or the sockets of course, but it's 100% consistent and repeatable while bad sockets are usually intermittent).

 

[dave_m]

The chips are OK, so if it's that kind of problem it'd have to be the buffers (or the sockets of course, but it's 100% consistent and repeatable while bad sockets are usually intermittent).

OK, I was thinking of my 8032 where no RAM is socketed.

If all RAM has been replaced, you should make sure the -5V bias for the RAM is OK assuming they are the 4116 dynamic chips. Is the kernal ROM on sockets also?

 

[MikeS]

OK, I was thinking of my 8032 where no RAM is socketed.

If all RAM has been replaced, you should make sure the -5V bias for the RAM is OK assuming they are the 4116 dynamic chips. Is the kernal ROM on sockets also?

--
It's a 2001-8, the original with notoriously unreliable single-supply 6550 RAMs and almost-as-bad 6540 ROMs, but I do have two of them and swapping chips confirms that they're all OK.

I've been beta testing a little adapter that Jim Brain is going to sell that replaces a 6540 ROM with a standard 2716 and with a few jumpers and a gate I managed to replace the whole set with a single 27128; interestingly it now boots but there are some anomalies in the display that lead me to suspect that the problem is with the memory addressing. I'll check it out tomorrow and maybe replace the RAM with a 6264 while I'm at it.

Surprising considering their bad rep, but with all the testing of Jim's board and the sick PET I've probably removed and replaced every RAM and ROM chip literally dozens of times and AFAIK not had a single problem with the chip sockets (even with mildew growing on the caps from sitting in a damp basement)

Getting there...

 

[dave_m]

I've been beta testing a little adapter that Jim Brain is going to sell that replaces a 6540 ROM with a standard 2716 and with a few jumpers and a gate I managed to replace the whole set with a single 27128; interestingly it now boots but there are some anomalies in the display that lead me to suspect that the problem is with the memory addressing. I'll check it out tomorrow and maybe replace the RAM with a 6264 while I'm at it.

Mike,
Any update? Or did you let yourself get distracted by other projects?
-Dave

 

[MikeS]

Mike,
Any update? Or did you let yourself get distracted by other projects?
-Dave

Yeah, distracted by other projects and 'real life'. I only dug out the PETs to test Jim's ROM adapter and thought I'd have a quick look at the dead one while I was at it; then some CP/M and Tandy M100 stuff distracted me and the coming winter is making some outstanding 'projects' around the house more urgent.

But maybe your reminder is what I needed to get me back on track... Thanks!

mike