A test you might try... find one or two fairly large
(value) Electrolytic Capacitors as (or similar to the
one already) installed in the power supply.
With relatively short clip leads or decent wire, parallel
one of the filter caps across the original Power Supply
filter and if you have a second test cap, parallel it on
the supply output.
Then test to see if your crowbar trips.
cheers,
skipp
--- In [email protected], "Ed" <ed.bathg...@...> wrote:
>
> 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
>
