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Replacing the power supply in a Commodore PET 8032


Aug 4, 2015
Prior Lake, MN
Picked up a CBM 8032 with a bad transformer a few years back. Posted about how to fix here


and finally got around to cleaning up the wiring and permanently mounting the parts. Here's the parts list

Mean Well LRS-150-24 (https://www.amazon.com/gp/product/B018RE4CWW)
XL4016 Buck Converter x 2 (https://www.aliexpress.com/item/32915705218.html)
-9V DC-DC Negative Converter (https://www.aliexpress.com/item/32902764735.html)
CH3.96 9p Connector and Terminals (https://www.aliexpress.com/item/32808935696.html)
IEC Power Socket (https://www.aliexpress.com/item/32804170262.html)
Various 3mm bolts, wire, and crimps

The goal was to completely replace the stock (broken) transformer, storage cap, and wiring harness, but keep everything intact in case I ever run across a working transformer and want to restore everything back to stock.

After removing all the components (include the stock power inlet module with the evil RIFA filtering caps), we made these 3D printed brackets that allow you to mount the new PSU and buck convertors using the stock holes.


PXL_20210319_220804781 (3).jpg

IEC inlet is a simply L/N/G connection

PXL_20210320_162612208 (2).jpg

Adjust the PSU from 24V down to 21V (assuming you are using a 12" CRT). This will feed the monitor directly and the rest of the buck converters.

PXL_20210320_211302204 (2).jpg

Adjust the buck converters to +16V and +9V. The CH3.96 connector for the PET is wired as follows (with pin 1 towards the front of the computer). Pin 7 is the key pin, I filled mine with hot glue.


PXL_20210320_211307536 (2).jpg

Double check all the voltages before plugging into your PET board. Once satisfied, flip the switch.

PXL_20210320_214554012 (2).jpg

Everything looks pretty much stock from the outside.

PXL_20210320_230705222 (2).jpg

Album with higher res photos is here.