TRC-448 repairs

[Cable Guy]

I would look it over for backwards capacitors especially around the audio chain. Also, the audio IC may not have survived the abuse.

 

[DTB Radio]

I think you are on the right track with looking at the audio amp section. I've run into other makes/models with similar issues that traced to audio amp issues. As was mentioned, look for cap faults, especially bypass and feedback caps.

 

[TM86]

I've had to put this one aside for now. I keep overthinking what it could be and end up going in circles.

So, throwing it on the shelf until I'm smarter. Hey, it worked for the MonkeyWards radio.

Moving on to other projects that have been stacking up...

 

[doffo]

I've had to put this one aside for now. I keep overthinking what it could be and end up going in circles.

So, throwing it on the shelf until I'm smarter. Hey, it worked for MonkeyWards radio.

Moving on to other projects that have been stacking up...

I purposely put radios up on the highest shelf in the garage so I can't reach them without a ladder.... Some year I will get them back down lol.

 

[Cable Guy]

I've had to put this one aside for now. I keep overthinking what it could be and end up going in circles.

So, throwing it on the shelf until I'm smarter. Hey, it worked for MonkeyWards radio.

Moving on to other projects that have been stacking up...

That is very sensible. If you keep learning, you will one day be equipped to repair it. When discouraged by my lack of knowledge and skill I say to myself "I am not smart enough today, maybe next week or next month I can fix it". Let it rest awhile and with enough time and thought, look at it again and the issue becomes obvious. Just don't give up.

 

[TM86]

That is very sensible. If you keep learning, you will one day be equipped to repair it. When discouraged by my lack of knowledge and skill I say to myself "I am not smart enough today, maybe next week or next month I can fix it". Let it rest awhile and with enough time and thought, look at it again and the issue becomes obvious. Just don't give up.

When it's that or throw it against the wall, I'll put it on the shelf every time. I did the drywall in here, I don't want to have to do it again.

 

[brandon7861]

I'm looking at the block diagram and it looks like the only thing keeping the mic audio out of the speaker amp is a little tx/rx switch Q17.

Question. Does the oscillation frequency change with changing distance between the mic and speaker?

edit;
I suppose the mic switch stops mic audio, but idk. havent looked that far., yea, nevermind.

edit2:
lots of switching diodes... Lou's book mentions those can cause squeals