Bottlehead Kits > Eros Tape

Shunt regulator readings [resolved]

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PS2500:
Also, I assume you mean that the problem is on the B side of the board? I have taken some additional closeups of that area, though I'm not sure if they show much that isn't visible in the first three photos I posted. I'll add them if you think it might help, but just wanted to confirm first that you're talking about B, not A.

Paul Birkeland:
Some things I would look at:

1.  Check that the wires going from Kreg to pins 3 and 8 on the 9 pin socket are going to the correct places.  The same goes for the wires that attach to pins 1 and 6 on the 9 pin socket.  When I have switched a pair in the past, I have experienced strange behavior like this where half the regulator will work and the other half will not.  If one of the 220 ohm resistors going to the D socket is damaged or poorly connected, it could also cause odd problems like this.

2.  Check that the 2N2907 transistors are in place and the 2N2222 transistors have not been accidentally substituted.  I don't think this is an issue for you, but I'd look.

3.  Check that the TL431 regulators are properly placed and not MPS4250 instead.  I also do not believe this is your issue, as I believe this makes the Kreg voltage take off pretty high.

4.  Check that the R1 resistors are the correct values. 

5.  Flip the PC board over and be sure everything is well soldered. 

6.  Set your meter to beep for continuity and be sure there are no shorts between any pair of legs on the TL431 regulator on that side. Repeat this test for the 2N2907 and MJE5731A.

-PB

Deke609:
It might be fine on the underside, but from the topside it looks like the circled connection point in the attached could use some solder.

PS2500:
Thanks Derek, I believe I checked that the other day to make sure the connection is good, though I may add some extra on top to be sure. I think all the connections on this board were soldered from the underside at the time of stuffing the board, and I did look pretty closely at those connections at the time. They appeared fine, but it's not apparent from the top.

Paul, thanks for your assistance and patience, I'll take a look at all those points you mentioned. I've already had a look (visual check so far) for any signs of shorting and there were none. I'm going to look closely at the 220 ohm resistors to start with, because soldering those in was no picnic.

PS2500:
I've done all the checks I'll have time for this weekend, unfortunately further checking will probably have to wait until next weekend.

Resoldered one of the 220 ohm resistors, just to be sure there was a clean joint and good connections.

Continuity tested the legs on 431 regulators (both sides), no beep. Continuity tested legs on both MJE5731A transistors, no beep. I haven't done this test for the 2N2907A's, because I need unrestricted access to the bottom of the board for that, which can't happen until I undo some wire connections. It doesn't just flip over...

Confirmed that both R1 resistors are 37.4 ohm. Confirmed that 431's are definitely 431's.

On retest, I still get the same voltages for the 2 red wires. When I get time to come back to this, I'm ready to take off the board and check all underside solder joints, look for shorting, and then redo all soldering of D1 terminals and wires, in case the problem is there. I've looked at it and all seems fine (no obvious shorts), but going back and redoing it step by step may be the best course now.

(Incidentally, I did get a better close shot of the B side of the board, which I attach here. But I don't expect it will reveal anything important.)

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