M1225 Distorted Audio

[KE7JFF]

A while back, I picked up a "tech special" VHF M1225 20-channel that was described as "always on once powered appied and no internal speaker installed". Once I got it and did some testing and found it has no further issues, but there was a sticker on it from the previous owner that said (was damaged due to misuse of accessory connector" I've been using it fine as a go-box radio for a while now with an external speaker connected to the right pins on the accessory connector.

However, the other day, I pulled the radio out and noticed all the RX audio was distorted, which I thought it was odd. I grabbed another 8-ohm speaker I had laying around and still way distorted audio. Volume still works; it obviously makes the distorted audio louder or quieter still.

Doing a quick search on the forums, I see there is mention of an capacitor that could be faulty that is 33 uF in the audio out path, but I can't find it anywhere. Anyone have any ideas for further diagnostics? Or am I on the right path with the capacitor?

[jackhackett]

I think I found the post you are referring to. I don't know what he was on about there, the capacitor he's talking about is in the Maxtracs, but M1225s are quite a bit of a different animal. There is a 1uF between the detector output and the audio opamp, which would be the closest thing to what he was saying.

Can you check the RX audio output on the ACC plug (pin 11) to see if it is distorted? If it is I would check that the radio is on frequency, and that the second oscillator is on frequency. You could also have a bad IF filter. If the ACC connector audio is okay then the problem would be in the audio circuits somewhere.

If you need a service manual they have it on the repeater-builder site.

[KE7JFF]

I'll take a look at it today at some point and get back to you. I do know that even with this RX issue, the TX side is transmitting fine and on frequency.