It is there to prevent an unexpected over-voltage at the output.
If there is no voltage at the output terminals but 20 or more at the collectors, then check the bases of the pass transistors sailor moon another story english for voltage.
Why not just use one or a couple of those mosfets in parallel to simply switch OFF the voltage output if triggered by the SCR?Those four pass transistors act as a bigger current amplifier.Astron RM60M 60Amp rack mount power supply with meters.Applying the math, that worked out to a full shut-down without the shunt resistor at almost exactly 16 volts.
A dead Astron bargain, i bought this piece at a hamfest.
However, the voltages can be checked with the circuit board still in place.
Astron VS-35M 2-15V 35A Tabletop Adjustable DC Linear Power Supply Module #2.
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Ham Radio Equipment For Sale: m Equipment For Sale Astron, astron RS-20A Linear power supply,.8V, 20A.There are two heavy wires soldered to the bus wire, one goes to the SCR and the other to the positive output terminal.I also check for shorts at the output to see if the over-current (foldback) function of the LM-723 may have kicked.If the board is freed to get to the components, I recommend using a bit of contact cleaner on the little variable voltage adjustment pot.Astron BB-30M Battery Backup Module, henry 100D-95 RF Amplifier.5 MHz 100 Watt Radio Unit w Astron Power Supply.I doubted that the spike had come from the power line since the factory-installed MOV across the transformer primary was intact.It was dead so the price was right.If the bulbs do not light it is also possible that the SCR has failed open.Mosfet over-voltage protection board installed in the Astron Do we even need an SCR?