help with Shunt Regulator

[denti alligator]

Stereomour II functioned perfectly before install.

Got the shunt regulator kit installed today. The LEDs on the board were only lighting up for A and not B, so I switched tubes, and then B lit up but not A. So I assumed I had somehow ruined one of the tubes and promptly went to my local guitar shop to pick up a new pair of 12AT7 tubes.

These, however, show the same problem. I switched them, and low and behold, the LED side switched. But then I couldn't duplicate it. I'd switch them back and A would still be out.

I just unplugged the unit to write this, and then plugged it back in to run voltage checks, and the side switched (!!) without me having switched the tubes! So now the A LEDs are lit and the Bs are not. Weird.

I can't figure this out, but voltages are off, so here they are:

IA  382
OA  228
KregA  8.83
IB  382
OB  382
KregB  1.9

Yep, I unplugged and waited two minutes and plugged back in and here are the new voltages (with other set of LEDs lit):

IA  381
OA  381
KregA  1.897
IB  381
OB  216.9
KregB  8.72

Note also that the LEDs on the small C4S board for IB were on at first and then went out. Note also that both sets of LEDs on the main board lit up at first, but within two-three seconds one set goes out. And yes, that set alternates seemingly randomly!

[Doc B.]

Try reheating all of the tube socket connections.

[denti alligator]

Done. Same problem. How do you account for it randomly switching channels? That's very strange, isn't it?

Just re-flowed them again, and also all the new joints. Still have one side out.

Seems pretty consistently now to be the A side that is out.

[denti alligator]

Never mind. I just tried testing it again and now the B side is out. This is weird.

Unless I hear from Doc otherwise, I'm going to go over every single new joint, including the pads on the board.

[denti alligator]

OK, I removed the main leads from the shunt board and reflowed all new joints, including those on the board itself. Then I reattached the leads. Same problem. A side LEDs are not lighting up.

I'm bummed. What could be the cause of this?

[denti alligator]

I just spent 1 1/2 hours working on this this morning. Reflowed all joints that might be a cause of the problem. Reattached a lead on one of the tube sockets. Nothing.

At least now it seems to be pretty consistently side A that is not lighting up. Is it possible that something on the board is not working as it should?

[kgoss]

Post a picture of the board - top and bottom.  Pictures plus voltages is the best and fastest way to get problems resolved.

[denti alligator]

IA  383
OA  380
KregA  1.864
IB  381
OB  240
KregB  7.97

(this is with the A LEDs not lighting up)

Last pics taken with IA wire disconnected (only way to get a good shot of the underside)

[denti alligator]

Went through everything a fourth (!) time, and found the problem!

I had reg+ for A and B sides mixed up. The reason for this is partly (mainly!) because I wasn't being careful enough, but partly because I was reading A and B *down* the side of the board instead of as halves of the board. That is, I confused where to draw the board's "half," because I was looking at the other A and B markings on *that side of the board*.  (Maybe something to stress in future manuals?)

Oh well, it's done. Now to crank it up and listen!!

[Paul Birkeland]

I've made that mistake a few times myself.  Sometimes the 431 regulators can cope with that error, but usually things get all out of whack.  I'm glad you got it sorted.

-PB

[denti alligator]

Thanks. Yeah, the change in sound was instantly noticeable. Sounds more detailed. More separation of instruments. I wouldn't say it's dramatic, but it is a clear step up--and totally worth it for the price!

Now to save my pennies for the Eros...