Driver testing: my OA reading is running around 350VDC instead of 300. Problem?

[thunderfrenchie]

It biases OK, and the IA reading is steady at 499. Is it OK to proceed?

Thanks,

John

[Paul Birkeland]

499V is plenty for IA, nothing to worry about there.

[Paul Joppa]

IA is fine, but the OA voltage is a problem (that was in the subject, but not in the body of the original post). It indicates that the Zeners are doing their job, protecting the C4S which is NOT doing it's job.

Time for voltage testing. kreg(B) would tell us something useful about what is going on.

[thunderfrenchie]

kreg(B) is coming in at 11.22. Also I have the DC PS.

[Paul Birkeland]

11.22V on Kreg indicates that half of the tube is drawing absolutely no current, but you said you were able to bias the other side with the trim pot?

This, in my mind at least, would point to a jumper miswire on the board.

[thunderfrenchie]

Hi, have gone over my assembly several times and am still having this issue.

On the left/black channel only I get:

IA--holding steady at 503
OA--.663vdc--this is the problem
B side LEDs do not light
Kreg B is 1.98

Photos below:

[Paul Birkeland]

I see lots of cold solder joints.  Here's an image of a good joint next to one that likely won't work.  If the solder doesn't flow all the way through the plated through hole, then you an assume that the flux in the solder has floated to the surface and is stuck between the solder and the component lead, acting as an insulator.

On parts like resistors and transistors, they can take a fair amount of heat to properly solder (LEDs and capacitors tend not to take so much heat).  The MJE5731A, for example, may need 5-10 seconds of iron heat on the middle leg to allow for the solder to flow properly.

-PB