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Old 9th Oct 2021, 9:47 am   #10
Join Date: Aug 2011
Location: Newcastle, Tyne and Wear, UK.
Posts: 7,513
Default Re: Commodore PET 2001 voltage regulators

Retromit, thanks for the detailed images. I should point out that as a new forum member your posts are held for moderation, after which they appear in their correct chronological position in the thread. When I posted #8 above your post #7 wasn't yet visible.

OK, so - As explained earlier, what should happen is that your 16V AC goes to a group of four diodes on the mainboard and is turned into +9V and -9V DC.

The +9VDC then goes back offboard out of JP8 pin 4 on a red wire to the + terminal of the large metallic blue capacitor mounted offboard, then comes back from there down another red wire and back in on JP8 pin 2. From there, it goes to the cathodes of CR10 / CR11 and the input terminals of the two 5V regulators.

From your measurements so far you have the AC voltage (about 16V) going into the board on JP8 but you don't seem to have the DC voltage which should be coming out of the rectifiers, so the supply is going missing somewhere in that area.

I'm about to go out for the day, have a look in the general area of JP8 - lift the board and look at it for problems like cracked solder joints underneath, especially on JP8 itself. If you need more specific point to point help with tracing the problem I'll sit down with the diagrams later and try to give you an exact list of points to measure between. (Anyone else who can do this earlier, please pitch in).
SiriusHardware is offline   Reply With Quote