Needs help on understanding the operation of this schematic.

Thread Starter


Joined Nov 26, 2011
Hi all,
I have bought this power supply from a local auction and found out the reference was bad. After inspection, I realized that the thermostat in the oven assembly was bad and over cooked everything inside. I have attached the schematic. I am going to replace the +ref and -ref with LM399 and LT1001. But I am having trouble understanding the operation of the diff pair. Why they are biased differently. Why Q5B collector is connected to virtual ground but Q5A is connected to VG+Vref.
Any inputs will be highly appreciated !