Failed Final Voltage Check

[Paul Birkeland]

With the front C4S board disconnected, can you recheck the IA, IB, OA, OB, KRegA, and KregB voltages so we know where things stand at the moment?

[Dhouse7516]

After reconnecting the board, with the blue wires disconnected from the front board, these are my voltage readings.

IA: 288
IB: 288
OA: 285
OB: 228
KregA: 6.36
KregB: 2.5

[Paul Birkeland]

The B side R4 seems like it may not be well soldered on both ends.

[Doc B.]

That's what I was thinking. B side breg pads look like they could use a reheat.

[Dhouse7516]

Okay, thanks. I'll give it a shot.

[Dhouse7516]

I reflowed all of the Breg pads, the +reg pad, and the pad at the other end of the R4 on the B side, and I am still getting the same voltage readings as posted above.

[Dhouse7516]

I also tested at the R4 pads, and they are good at 219K ohms.

[Paul Birkeland]

Is the jumper leaving OB well soldered on both ends?

The 6V cathode 288V on the plate to me seems like the regulator on that side just isn't connected somehow.  Also be sure the 431 regulator is there and not an MPS4250.

[Dhouse7516]

The 431 regulators are both in the right place. I will double-check the OB jumper tonight. Thanks.

[Dhouse7516]

Well, I stepped away for a bit and then took another shot at this. I reflowed all the D-Socket and shunt board joints and reconnected the board above the D socket. My measurements are below. I suspect that I may have damaged one of the traces on the shunt board. I hate to admit defeat, but I might need to send it in to y'all. Let me know if you have additional suggestions. Thanks much.

IA: 290
IB: 289
OA: 282
OB: 155
KregA: 6.41
KregB: 4.5

[Paul Birkeland]

Typically that set of voltages would have me double checking that the wiring going to the 9 pin socket is all routed properly.  If you swap a pair of the wires going between that board and tube socket, you can end up with wonky voltages like this.

If you are unable to remedy this issue, you can contact queen(at)bottlehead(dot)com about ordering a repair service.  Be sure to send her a link to this thread so she knows we have worked on the problem here.

-PB

[Dhouse7516]

Yep, I triple checked all of those wires, and reflowed the solder for all of them. It's all good. Are there any issues on the board that you can think of that might cause these voltages? Anything I should focus on in particular? I've confirmed that the regulators are in the right place, reflowed the solder to the R4, and confirmed that BREG is connected to +Reg. Is it possible I have a defective or damaged regulator? I tested the resistor and it measured fine.

[Paul Birkeland]

A defective regulator will typically short out and you'll see 1.8V or so on Kreg and low OA or OB voltage.

[Dhouse7516]

Got it. When you said above that the cathode and plate voltages caused you to think the regulator wasn't there, it made me think that a defective regulator could also cause the voltages. Anything else I should focus on?

[Dhouse7516]

So the red wire connecting the B side of the shunt regulator to 28L just snapped off at the BReg joint as I was lifting the board to re-check my wiring. I'm guessing that it got damaged with all the fiddling I've been doing. Would that cause the voltage readings I was getting (if it wasn't properly connected to the board)? In any event, I will replace it and see what that does, once I can find some wire. It's 22AWG, correct?