Having problems with a SPECTRUM 4000 UHF repeater that the voltage regulation works ok on RX, but when you kick it into TX, the SCR fires and blows the fuse or frys the resistor.
This is the newer version power supply board that has the current limit control on it. We replaced the SCR and .25 ohm dump resistor, and it still triggers. I watched it trigger 2 times last night with a digital meter on the circuit and saw no overvoltage contition, at least not what the dmm registered. Theory: Could a bad cap be letting RF back into the crowbar circuit, causing the SCR to trigger from the RF rather then DC? Please Advise Ed N3SDO
