Traynor Reverb Mate 40 strange breakup

[pontiacpete]

This amp is doing something strange, it breaks up with the reverb on only.
I was certain it was a blown speaker but found that it does it with other speakers.
THe other strange thing is that it does this distorted breakup only around the open G frequency.
I swapped out the reverb tank and still the problem exists.
Could the associated IC cause this sort problem?

I take this back, I think this breaking up is happening with or without the reverb.
It's hard to tell because it was much more obvious with the reverb on.

[pontiacpete]

Don't know if this matters but
when touching the top of C114 with a meter probe a loud high pitched squeal comes out.
and touching the top of C105 tunes in a radio station

[pontiacpete]

pictures of the output while in ch 1. As the gain is increase the notch in the square wave appears.

[soundguruman]

Don't know if this matters but
when touching the top of C114 with a meter probe a loud high pitched squeal comes out.
and touching the top of C105 tunes in a radio station

Is it a good rock and roll radio station?

[pontiacpete]

It's a spanish speaking channel, probably talk radio.

[52 Bill]

A couple of questions here.

This is a stereo output amp, where are you monitoring the output?

Why are you using a square wave for testing?

Is the distortion on both left and right speakers?

[nickb]

Don't know if this matters but
when touching the top of C114 with a meter probe a loud high pitched squeal comes out.

I bet you have a DVM? That is a very sensitive point. You are probably hearing noise from your DVM signals.

and touching the top of C105 tunes in a radio station

Your lead is just an antenna. Don't worry about it.

[pontiacpete]

Right, I am now put the dummy load on both sets of speaker terminals a nd the same notched wave is there

I'm using a sinewave. It squares off quickly with reg volume pot on 2 and gain volume at about 2 and then starts to notch.

yes the distortion is in both speakers.

[DrGonz78]

Are any of the IC's or output transistors heating up? What sorts of voltages are present on the amp...?

Edit: BTW I remember working on this same amp about a year ago and it had some major flaws from the factory. I remember soldering a chassis ground wire to the back of the reverb pot. Probably not very good solution for your problem but it brought down the hum on the reverb. Your problem sounds way more involved than what I experienced. I did find that one of the output transistors was missing a screw spacers and was about to explode. I would be looking at those IC's first to see the voltages.

[pontiacpete]

Thanks everyone,
I pulled the board out and resoldered all joints and it's working.
Strange thing was that it didn't seem to react to the usual banging on the chassis.

[soundguruman]

It's a spanish speaking channel, probably talk radio.

At least it wasn't Rush Limbaugh...