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Power Supply Repair in 8566B

Question asked by DaveWave on May 31, 2010
Latest reply on Dec 16, 2014 by pcunagin

Here's an oldie but a goodie for you:

I have an 8566B SA system that has a power supply problem.  I have traced the failure to the series-pass regulator transistor in the +20 V supply.  This is a TO-3 case transistor mounted to a heatsink on the motherboard and real panel of the unit.  The service manual refers to this device as "A23Q3" with A23 being the motherboard subassembly.  However, Q3 is missing from the list of replaceble parts for A23.  It also is not listed with the A17 and A8 subassemblies which are the rectifier and regulator sections that it actually connects to.  There is no cross-reference to it anywhere in the manual that I can find and it only has what I believe to be an HP part designation on it.  It is marked Motorola part "4-618".  Does anyone know what standard Motorola part this is or does anyone have a manual that correctly references it?  Thanks!  Dave