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Old 8th Oct 2021, 2:32 pm   #3
SiriusHardware
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Join Date: Aug 2011
Location: Newcastle, Tyne and Wear, UK.
Posts: 7,539
Default Re: Commodore PET 2001 voltage regulators

Although not the reference you quoted, all the part numbers in this circuit diagram match those you have quoted.

http://www.zimmers.net/anonftp/pub/c...01N/320349.pdf

What's not clear from this diagram is that the AC power for the +9V and -9V supplies comes in from the transformer on J8 pins 1 and 5 (so check across those two point for AC Volts) and then +9V comes out from the bridge rectifier on JP8 pin 4, goes to the +Ve of the large capacitor on the offboard power supply 'lump' and then comes back onto the board via JP8 pin 2. From there it goes to the input pins of the two +5V regulators, so if you have no output from both of the +5V regulators the most likely reason is a missing +9V supply to the regulator inputs.

So try looking for:

...AC volts across JP8 pins 1 and 5

...Around +9VDC (with respect to 0V) on the following points in turn:-

...JP8 pin 4

...+ve terminal of the large offboard capacitor

...JP8 pin 2

...CR10 cathode / CR11 cathode (the ringed ends of the diodes).
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