Driver Testing error (RESOLVED)

[Paul Birkeland]

OK, so that tells us that the zener string is installed and working properly, and that the A side of the C4S appears to be working properly. 

Some things I would check are:

1.  Does this happen with all 5670s?
2.  Are the red wires leaving OA and OB going to the correct places?
3.  What is the Kreg voltage on the B side of the board with the issue?

-PB

[Urbansandz]

Thank you Paul.

1. Yes, issue persists after switching tubes.
2. OA goes to +reg B, and OB goes to 46U
3. B Kreg = 1.8 VDC. On the A side board it's 7.36, so that must be where the problem lies, though I don't know how to remedy. Replace the TL431 on the B side?

[Paul Birkeland]

Yes, I would put a new 431 in on that side.

[Urbansandz]

I replaced the 431 on the B side, but no luck. I'm still getting ~145 VDC on OA and 1.8 VDC on Kreg(B).

[Paul Birkeland]

What's the DC voltage at the random pad marked with the "X" on the B side?

[Urbansandz]

The x on the B side is measuring 2.65 VDC.

[Paul Birkeland]

How about bB?

[Urbansandz]

OK, yeah, there's a problem there. I'm getting ~72 VDC at bB.

[Paul Birkeland]

Can you verify that the R1 resistor values are in the correct spots?

[Urbansandz]

R1(B) is measuring at 215 Ohms.

[Paul Birkeland]

At this point it would be super helpful to trade the PC boards between sides.  If the OA voltage stays on the same socket, then we need to figure out what's going on with the socket wiring itself.  If the OA voltage moves with the board, then there's something wrong with the PC board population/jumpering that just hasn't been noticed yet.

[Urbansandz]

I switched the boards and the issue remained with the board. The OA was still 145 VDC on the board that was previously on the D side and now moved to the A side. I've attached photos of the two boards. The problem board is on the left in both photos.

[debk]

Hard to tell from picture, but the black wire going from bA to -reg has a long bare area at bA.  Could this be touching one of the pads on the pot especially when the wires are compressed when attaching the board?

It's a long shot


Debra

[Paul Birkeland]

I would set your meter to continuity beep and be sure none of the legs of Q1 on the A side of the funky board are touching.  It's possible you may have a teeny tiny solder bridge causing problems there.

[Doc B.]

Underside pic - right hand board - looks like a cold joint on a 431 pad. The row of pads above IB, fifth pad in from right.

Topside pic - left hand board - possibly a cold/missed connection at the bA pads next to the blue trimpot. Though it seems to look OK on the underside. I'd reheat just to be sure.