Commodore PET 2001-C

[adko]

Hello everyone, I bought a Commodore PET 2001-C and am restoring it
Now I saw a bit of oxidation on one type of resistor on the motherboard, now my question can this remain that way or should this be remedied and how do i do this?
And does anyone know the type number of this motherboard because this number has been made unrecognizable
See my photos and thank you very much in advance
Greetings Ad

 

[VERAULT]

Those are diodes not resistors and I see no problems at all. It looks perfectly fine to me. I do see some old flux residue. you can easily clean that off with rubbing alcohol and a toothbrush.

 

[daver2]

+1. They are diodes and just a little bit of corrosion/flux residue.

That is a 320351 assembly from a 2001N. You can find all about it here: https://zimmers.net/anonftp/pub/cbm/schematics/computers/pet/2001N/index.html.

I am not sure that PCB actually came with that machine though. I suspect it is a later upgrade.

Nice to see it works though.

Dave

 

[Hugo Holden]

I would not consider replacing any parts on that pcb unless there was some evidence of a defect, except perhaps the green Tant capacitors because at this age they have a penchant to spontaneously short out. However, in this case, you can also not have to do it, until the capacitors do short out, because the voltage regulator types on these boards are excellent at going into current limiting mode when overloaded, so the shorted Tant capacitor doesn't result in vaporized pcb tracks as it can in some circuitry. So its quite reasonable to leave those capacitors alone until the fail.

 

[adko]

Those are diodes not resistors and I see no problems at all. It looks perfectly fine to me. I do see some old flux residue. you can easily clean that off with rubbing alcohol and a toothbrush.

Thank you , i go do that

+1. They are diodes and just a little bit of corrosion/flux residue.

That is a 320351 assembly from a 2001N. You can find all about it here: https://zimmers.net/anonftp/pub/cbm/schematics/computers/pet/2001N/index.html.

I am not sure that PCB actually came with that machine though. I suspect it is a later upgrade.

Nice to see it works though.

Dave

Thank you for all this info
I go read it

I would not consider replacing any parts on that pcb unless there was some evidence of a defect, except perhaps the green Tant capacitors because at this age they have a penchant to spontaneously short out. However, in this case, you can also not have to do it, until the capacitors do short out, because the voltage regulator types on these boards are excellent at going into current limiting mode when overloaded, so the shorted Tant capacitor doesn't result in vaporized pcb tracks as it can in some circuitry. So its quite reasonable to leave those capacitors alone until the fail.

thank you for this information, good to know

 

[Hugo Holden]

Your board may well be one of the last production runs of the Dynamic PET board, most of the date codes on the IC's are 1979, so it is possible it could have been made in 1980 too.

The purple ceramic body 8116 DRAM IC's (equivalent of the 4116) look quite lovely. They will be excellent DRAM IC's. Probably explains why they are still working. Many of the poorer quality types have failed by now.

You even have ceramic equivalents of the 2114 SRAM IC's, and no surprise, they are still working. You may well have one of the most perfect dynamic PET pcb's on the Planet. (you can't count the ones that the Aliens took off planet to study Commodore's technology, ha ha).

I fitted my dynamic PET board with purple ceramic 4116's too, but I could not find the Fujitsu ones that yours has. However, I found some that were made by the USSR's military/industrial complex that appear equally as good and reliable. I bought out the remaining stock from the sellers who had these in Ukraine. IC's built on a ceramic substrate are better than ones in epoxy housings, especially as many decades pass by since they were made, because ceramic & glass is physically more stable than plastic. The 4116 DRAM IC is amazingly internally complex, much more so than any typical logic IC in the same sized package.

You will notice on most of the board where IC's were soldered in etc, there is no flux, as it was all cleaned away after the wave soldering. The diodes and a few other parts in the power supply area were fitted last, by hand soldering, and that is why the flux is still there.

If you want, you could clean that flux off, using cue tips and some CO contact cleaner made by CRC.

 

[adko]

Your board may well be one of the last production runs of the Dynamic PET board, most of the date codes on the IC's are 1979, so it is possible it could have been made in 1980 too.

The purple ceramic body 8116 DRAM IC's (equivalent of the 4116) look quite lovely. They will be excellent DRAM IC's. Probably explains why they are still working. Many of the poorer quality types have failed by now.

You even have ceramic equivalents of the 2114 SRAM IC's, and no surprise, they are still working. You may well have one of the most perfect dynamic PET pcb's on the Planet. (you can't count the ones that the Aliens took off planet to study Commodore's technology, ha ha).

I fitted my dynamic PET board with purple ceramic 4116's too, but I could not find the Fujitsu ones that yours has. However, I found some that were made by the USSR's military/industrial complex that appear equally as good and reliable. I bought out the remaining stock from the sellers who had these in Ukraine. IC's built on a ceramic substrate are better than ones in epoxy housings, especially as many decades pass by since they were made, because ceramic & glass is physically more stable than plastic. The 4116 DRAM IC is amazingly internally complex, much more so than any typical logic IC in the same sized package.

You will notice on most of the board where IC's were soldered in etc, there is no flux, as it was all cleaned away after the wave soldering. The diodes and a few other parts in the power supply area were fitted last, by hand soldering, and that is why the flux is still there.

If you want, you could clean that flux off, using cue tips and some CO contact cleaner made by CRC.

Thank you for this good information, you know a lot more about it than I do I will delve deeper into this PET thanks again, greets Ad