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Old 8th Oct 2021, 1:26 pm   #1
Join Date: Oct 2021
Location: Edinburgh, Scotland, UK
Posts: 136
Default Commodore PET 2001 voltage regulators


Iím wondering if you can help me. I have a Commodore PET 2001 (assembly 320351) and Iím in need of some advice for the voltage regulators VR4 and VR3.

To give some background, it was bought locally and had been stored in a loft. I bought it non-working, but it did boot (had a garbled screen). Looking over some other posts, it seemed like it could be a video RAM problem Ė so I replaced the two MPS2114 with two MM2114N-3 (from a Commodore 64). This solved the garbled screen as it showed the Commodore BASIC text, as well as the memory available Ė good news. After switching it off then trying again later, nothing was displayed on the screen.

I checked the voltages for VR6 (-5.06v) and then CR12 (+12.16v). On checking CR11 and CR10, they both showed voltages of around 0.48v. So, Iím thinking the voltage regulators for the 5v line may have gone (hence nothing appearing on the scree - although I could be wrong here). The PET I have has LM323K STEEL regulators for the +5v.

What Iím asking is do you know of any modern replacements for the LM323K STEEL which you could recommend, and would it also be prudent to change the +12v at the same time?

Thanks in advance, and please let me know if you need any further details or have any further ideas/suggestions on what Iíve detailed.
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