Voltage check high shunt regulator

[edphones]

Hello,

After realizing I'd installed a PN2907A in reverse, I removed the solder and set it properly, but hope that I didn't damage the board or the part in the process.

MJE5731A tabs are 352V on A and B (at least it's consistent?). I've validated the connections to the power supply board and to the D socket terminals are as they need to be.

Are there other voltage checks that might help me narrow down the issue? I had good values off the power supply board.

Regards,

Ed

[Paul Birkeland]

What are the Kreg values?  Is the 12AU7 glowing?

[edphones]

The tube glows -

Kreg values are 1.8V, both A and B-sides

I set all the tubes (although I think the test only requires the 12AU7 is set), and retested to see I was now getting a good reading for the shunt reg voltage test.

MJE5731A tabs:

   A-side = 215V
   B-side = 213V

On my first test, I had an instantaneous reading of 352V when first plugged in and stopped there. When I went to retest it seemed like the voltage started off as high as I had previously reported. It then dipped fairly quickly to as low as 205V to stabilize at the above values, which are in-range. They stayed there - is this a warm-up or burn-in effect perhaps?

I think I'm good to continue unless there are additional checks that make sense at this point.

Thanks for the help,

Ed

[Paul Birkeland]

Either you didn't wait long enough for the 12AU7 to warm up and allow the regulator to work, or there could be a loose connection that's making that board work intermittently. 

[edphones]

Thanks Paul,

Since I run the Crack headphone amp I should have realized the behavior is consistent with a warm-up period of about 15-20 seconds. I've repeated the exercise and after warming-up, the voltage is steady and in-range. I'll continue and keep an eye out for anything odd.

After a few minutes to warm up completely, I measured a steady value for each side:

MJE5731A tabs:

   A-side = 215V
   B-side = 217V

Thanks again,

Regards,

Ed

[edphones]

Hello all,

The situation is a bit different than I originally stated - I skipped two sections regards the diode on the PS board, and the 2.49K resistors on the shunt regulator board. So my prior readings are meaningless.

I installed the missed parts and had a bad reading on A of 171.5V, and a good reading on B of 219.0V. I detached the shunt board and revisited each solder, and each step around the D tube socket and board. I found a suspect attachment for a ground wire at 31U, cleaned up a few connections I didn't like, and removed excessive solder. I didn't find any additional errors. I double-checked that the correct wires were going to and from the right locations. I checked all the jumpers on the back of the board.

Reassembled everything and similar result. That's disheartening, but leads me to think I have a bad part or attachment on the A side of the shunt regulator board. Tube is glowing, four LED glow. I also swapped out the 12AU7 to make sure that wasn't the culprit.

Relevant voltages, below. Any help is appreciated, as I'm not sure of the best way forward.

A side:

MJE5731A tab = 171.7V
Kreg = 0.361V
Breg = 171.7V


B side:

MJE5731A tab = 219.0V
Kreg =  2.480V
Breg = 219.0V

Voltage off the PS board at +275 = 284.0V

Regards,

Ed

[Paul Birkeland]

Can you list the parts you left off the board?  Doing that could possibly damage some components on the board.

D socket wiring issues can also cause those voltages to not be correct, specifically how well attached the resistors are that go to D2 and D7.

[edphones]

Sure, that's a real possibility I fear. Thanks for the help.

1 — 1N5262B diode (the diode on the PS board), page 33, and
2 — 2.49KΩ resistors (red, yellow, white, brown, brown), on the shunt regulator board, page 47

I did install the resistors attached to D2 and D7 very close, and I will look again.

Regards,

Ed

[Paul Birkeland]

You may well need a new 431 regulator on the side that isn't working.

[edphones]

Thanks Paul - I will get a new 431 regulator and report back. I'll also re-check the connections of the D2 and D7 resistors.

Regards,

Ed

[edphones]

I'm wondering about this as a replacement part or if I should write to bottlehead for a replacement?

https://www.digikey.com/en/products/detail/texas-instruments/LM431ACZ-LFT4/3901931

Regards,

Ed

[Paul Birkeland]

Yes, I would just order that.  The bosses are out of town at the moment, so there will be a little bit of a delay in providing a replacement from us.

-PB

[edphones]

Thanks Paul,

I did examine and re-flowed the solder for D2 and D7 to be sure I didn't jostle them but same deal. I'll get the part and let's see how that does it.

Regards,

Ed