MSF 5000 power cycles after warming up

[tskilbride]

I have a MSF 5000 that wouldn't key up, it would power cycle when it tried to key. I replaced the TX Power Adjustment pot and unit will now key. For testing purposes, I set power output to 60W out of the duplexer. It works fine until it gets warmed up, then power cycles until it cools off a bit and will eventually start to work again until it starts warming up. I then backed the power down to 50W, worked fine for a bit, then power cycle. I kept backing the power off and the repeater started working flawlessly at 30W out of the duplexer. I left the SWR meter in-line and didn't notice any power fluctuation in any of my power settings and SWR's are flat. This a analog UHF brought down to 442.950. Any ideas?

Thanks,

Tim

[kcbooboo]

Power supply, either the main one, or the 5V regulator on the SCM. If the incoming voltage drops low enough under transmit conditions, the station will reset. Check the voltage feeding the PA when the station is transmitting; it should be around 14V and it should not move around very much. The power control circuit is extremely sensitive and will do its best to maintain the output power at a constant level, even as the input DC voltage changes.

There are a few caps on the SCM that most likely need to be replaced as well, all in the power supply circuit.

Bob M.

[bernie]

My two bits worth:
I would highly suspect that the electrolytic caps on the main power supply are bad.
If the station has battery stand by option with NO battery, the regulator should be set to 14.5V because the regulator is very slow to respond.

The reason the station resets when keyed is that the input to the 5V supply sags so much that the +5V drops out of spec, triggering a reset.

If the power is set very low the station may work.