Left channel issues

[nmatlin]

Hi all,

I have been struggling with a left channel issue on my Stereomour II. I have all of the mods installed and have wiggled everything around with a chopstick, reflowing a lot of my solder joints especially around the shunt regulator board. I thought I finally fixed it yesterday, then, upon firing it up later, I realized that the issue is still persisting.

What happens is that, frequently, the D1 LED goes out and this affects the C4S board. When this happens, voltage on IA on the C4S board goes down to zero from ~304 or so. I've been looking around where to fix this -- but need some input on where the issue might be.

Best,

Nick

 

[Paul Birkeland]

This is the IA voltage on the small C4S board?

This can be from a wide variety of causes, but I would look at the 9 pin tube sockets and be sure that none of the pins are touching each other. It's possible to have a plate pin (either pin 6 or 1) touch a grid pin (either pin 2 or pin 7), and that would drag the high voltage output of the regulator down to zero. I've found on some Stereomour repairs that people will wrap component leads around the sides of the tube socket pins, and this is a surefire way to manifest this issue.

-PB

 

[nmatlin]

Hi Paul--thank you! It is actually the right channel--my apologies.

I have checked the sockets and found everything fine there.

If I wiggle the movement of the shunt regulator board, the voltages are fine on IB. But when the signal falls out, OB drops to zero and Kreg drops from normal range to 1.2. -- from standard range to around zero. +Reg also drops.

There must be a cold joint somewhere, but I've redone most of them and am still running into channel issues.

Thanks for your help!

Nick

 

[Paul Birkeland]

It could be a cold joint or a broken wire, but it could also be something intermittently touching that shouldn't be.

 

[nmatlin]

I worked on it earlier today. I think it was a cold joint on the transistor on the B side of the shunt regulator. We shall see if it’s settled once it has heated up and cooled down a few times.

Thanks, as always, for your help!