Could it be RF triggering the SCR?
Jerry W9FS
----- Original Message -----
From: Ed
To: Repeater-Builder@yahoogroups.com
Sent: Thursday, October 15, 2009 9:17 AM
Subject: [Repeater-Builder] Spectrum UHF Repeater SCR Crowbar circuit
activating during TX
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
