This is my Astron RS-20M 12 volt (13.8) 20 amp power supply that I picked up used a few years ago. It has started shutting down with a over voltage issue. I determined the output transistors were the issue.
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00:00 Intro and a look around
01:33 The inside view
02:16 The schematic
03:23 The protection diode I installed
04:27 Unsoldering the base drive
04:54 Testing with base drive disconnected
05:33 Testing the old transistors
06:35 Testing with the MK-168
07:16 Testing the new transistors
07:53 Installing new transistors
09:00 Trying Super Lube heat sink compound
09:14 Testing with base drive disconnected
09:49 Cleaning the board with ACETONE!
10:10 Blocking diode addition in the 90s
11:02 Testing with full (up to 140) AC volts
12:11 Final thoughts/Closing words