Astron RS-50a. Understanding circuit

[Vin]

I have aquired a broken Astron RS-50A psu. I can repair it, but I don't want it to go self destructive again. I do not fully understand the circuit. It would appear that if the crowbar fires, it will cause Q2 and the 2N3771 to fail before the overcurent 'protection' circuit kicks in. In particular, I cannot understand the purpose of diode CR5, or the reason for making the parralell resistor R1X a select on test component. Please help.
It would appear that an event caused the crowbar to trigger, causing massive current to flow from the 723 through the tip28(9), then via CR5 and the base emmitter junction of the 3771 driver. this took out these devices, then the 723 itself, then the 2 35Ampo stud diodes. And I suppose a fuse, although this was ok when I received the unit.
Thanks. Schematic is here
http://www.repeater-builder.com/astr...0m-1996-03.pdf

[AE6ZW]

crow bar circuit triggering ( SCR1 ) does not cause massive current in Q2 or 2N3771 following Q2, it will cause massive current flow in Q101, Q102 pair of 2N3771 however. because they all work as current amplifier, so LM723 or Q2 does not draw much current, 2N3771 followed by Q2 amplify current from Q2, and Q101 , Q102 amplify at the last, those transistor have current amplification factor ( Ic / Ib Beta ) over 100.
to fix those power supply, I have found often R101, R102 0.05 ohm resister, usually big white cement power resister burn up( become OPEN ) before Q101 or Q102 burn up. and found CR101 , CR102 sometime go bad. so you might want to check those first , since they are most common failure point.

[89DX]

crow bar circuit triggering ( SCR1 ) does not cause massive current in Q2 or 2N3771 following Q2, it will cause massive current flow in Q101, Q102 pair of 2N3771 however. because they all work as current amplifier, so LM723 or Q2 does not draw much current, 2N3771 followed by Q2 amplify current from Q2, and Q101 , Q102 amplify at the last, those transistor have current amplification factor ( Ic / Ib Beta ) over 100.
to fix those power supply, I have found often R101, R102 0.05 ohm resister, usually big white cement power resister burn up( become OPEN ) before Q101 or Q102 burn up. and found CR101 , CR102 sometime go bad. so you might want to check those first , since they are most common failure point.

I also have one, an RS-50A non-meter, which will provide right about 1/2 of the potential 50a of current before it goes into cardiac arrest and the voltage drops like Soviet space junk.

It never goes into any form of protection, nor does it act up as long as I pull less than about 25A.

Ideas?

- Gratsi!