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Author Topic: Shunt reg partially working  (Read 1807 times)

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Offline Bodyslam

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Shunt reg partially working
« on: October 20, 2014, 01:41:10 PM »
I'm putting together my Eros Tape, and when I got to the point of testing the shunt regs I hit a snag. The A side works fine. The B side however: D1 doesn't light up, D2 does, and there is no voltage on BO.

I've read through several threads where others had problems at this stage, so I had lots of things to try: re-soldered all the points on the board and on the socket. Measured the resistor values. With the board off, I double checked the wiring of the socket. Reassembled the board onto the socket double checking my work as I went. I even replaced the LED that was dark. I end up at the same place.

Here are some voltages:

IA 325         IB 325
bA 0.002      bB 0.001
KReg 5.44    KReg 2.41
+Reg 224    +Reg 0

And on the socket pins:

1-0.036
2-0
3-2.65
4-6.3
5-6.3
6-224
7-0.18
8-5.5
9-0.01

Any ideas?
« Last Edit: October 20, 2014, 01:46:21 PM by Bodyslam »
Paul Stubblebine
Paul Stubblebine Mastering, San Francisco
The Tape Project, LLC
serious student of the audio arts

Offline Doc B.

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Re: Shunt reg partially working
« Reply #1 on: October 20, 2014, 01:56:35 PM »
Hmm. Check the B side 2N2907 for shorts across its legs and make sure that the 37.4 ohm resistor is on spec.
Dan "Doc B." Schmalle
President For Life
Bottlehead Corp.

Offline Bodyslam

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Re: Shunt reg partially working
« Reply #2 on: October 20, 2014, 02:54:39 PM »
OK, pulled the board out again (sorry to say, I'm getting good at that.) The 37.4 ohm resistor measures 37.4 ohms. I inspected the area around the legs of the 2N2907--I had previously scraped it to be sure there were no bridges--still looks good. Measured from every leg to every other leg, both directions, and got either open or very high resistance readings: 300K or above.
Paul Stubblebine
Paul Stubblebine Mastering, San Francisco
The Tape Project, LLC
serious student of the audio arts

Online Paul Birkeland

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Re: Shunt reg partially working
« Reply #3 on: October 20, 2014, 03:48:47 PM »
Check for consistency in the red jumpers that leave OB and OA. 

-PB
Paul "PB" Birkeland

Bottlehead Grunt & The Repro Man

Offline Doc B.

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Re: Shunt reg partially working
« Reply #4 on: October 20, 2014, 04:29:03 PM »
Check the MJE5731A solder joints (and its orientation on the board). Some times the center pin in particular can require a little extra heat to get a good joint.
Dan "Doc B." Schmalle
President For Life
Bottlehead Corp.

Offline Bodyslam

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Re: Shunt reg partially working
« Reply #5 on: October 21, 2014, 10:05:06 AM »
OK, I tried hitting those legs with a little extra heat.

Also, I was on the lookout for anything that could be shorting the output, due to some comments from PB. The only thing that looked dicey was those two uninsulated resistor leads. Just to make sure that they didn't short anything when the card squishes everything under it as it goes down onto its mounting, I slipped some shrink tube over them.

Anyway, whatever did it, everything's working now.

Thanks for the guidance, and now on to the rest of the build.

Paul Stubblebine
Paul Stubblebine Mastering, San Francisco
The Tape Project, LLC
serious student of the audio arts