I'm looking for some troubleshooting advice.
As a new amateur, I've been given an old IC25a mobile and an astron RS-7a power supply to use with it. It works great on receive, but my transmit audio has a very bad hum problem - to the point that my voice is basically inaudible.
I know that this can be caused by an underpowered PS. The power supply is rated for 5A continuous, and the IC25 manual says it needs 4.8A on transmit. I've checked that the voltage across the PS terminals remains pretty much constant around 13.8V even on full power transmit, so I don't think that's a problem.
There is a slight hum present in the receive audio, but it's very quiet. This made me think the filtering in the PS might be shot, since this could obviously be more apparent at high load.
I've taken the main 42 mF filter capacitor out of circuit and tested it, and it appears to be working fine. I haven't tested any of the smaller capacitors since it's a fiddly process
Are there any other obvious things to test in the power supply?
Can anyone think of a way I can determine if the problem is with the power supply at all? I don't have another to swap out with it.
Is it possible the source of the hum could be the radio itself? It sure sounds like mains hum though.
I'm pretty confident there's no feedline or antenna problem; when I use the same setup with my HT it all works great.
With thanks for any advice,