Shunt test failure [resolved]

[nipsy]

I made it to the shunt regulator test stage and failed. Not sure what I've done wrong here and would appreciate another set of eyes on the project so that I might move forward. I'm hoping that my error is one of the dumb ones !

I read through the previous posts regarding problems passing the shunt test, but was unable to diagnose my problem.

During the first test I did not register any voltage on either of the MJE5731A. I removed the PCB to inspect the soldering. There were a few places where the solder looked insufficient and so I reflowed those contacts. I tried to clean things up a bit, but made a bit more of a mess in the process. I reattached the wires to the to the shunt board and tested again.

Nothing. 

The LEDs did not appear to light up.

Although I passed the glow test, the 12AU7 tube did not light up nor was it warm to the touch.

I tested the kreg on both the A and B sides of the board. Somewhere in the .324 range, though at one point I got a reading of 188 VDC, but was unable to repeat that reading.

I'm attaching pictures of my progress so far.

Thanks in advance for your help.

 

[nipsy]

Front of board

 

[nipsy]

Back of board

 

[nipsy]

More views

 

[Paul Birkeland]

With your meter clipped to the ground post like it is in the pictures, what DC voltage do you see at the +275V pad on the power supply board?  If that is also zero, then move your ground clip to the terminal on the power supply board next to the +275V one with the black wire leaving it and recheck.  The issue you're experiencing may have absolutely nothing to do with the second board you've installed.

 

[nipsy]

Thank you for your reply.

With meter clipped to ground post I get a reading of 1.1 at 275+.

Moving the ground clip to the terminal with the black wire coming out, 275-, I have a reading of 1.0.

I'm assuming I'd want to see a reading in the 275 +/- range, no ?

 

[nipsy]

After making certain that the fuse was intact, I went through the initial two tests again.

The powerline voltage test gave me 123.8 VAC.

I inspected the wiring and joints and they looked OK to me.

With the PSU and Shunt boards still attached (but 12AU7 tube not installed), I performed the secondary power test again.

1.1VAC between 7 and 9.

0VAC between 12 and 11.

Prior to attaching the the PSU Board, I got readings of 10.14 and 148.4.

Any thoughts on what I should inspect or measure next ?

 

[Paul Birkeland]

The AC voltages can also be measured at the power supply board, how are they there? 

Is your meter able to read a 9V battery? 

If the voltage coming out of the 275V pads is actually 1V, I would expect something to get incredibly hot and stinky in the process, so this may be an issue with measurement rather than the build.

 

[nipsy]

The meter seems to test multiple 9V batteries just fine.

I went back to the beginning of the wiring section to re-re-re check everything. You can't check too many times...

Switch resistance checked out: zero in the On position, OL in the Off position.

On the third check I discovered that I had reversed the wiring at 33L and 32L -- Black to 33L and Red to 32L. I'll put them in their correct places and recheck.

(First picture is the before, second is after)

Now when I check AC at 33U and 32U I get 0VAC !  Previous reading was 123.8 VAC.

One of the many odd parts here is that to have gotten to the shunt test, I had passed all the other tests. How could this have happened with the reversed wires ?

This is my third kit, 2nd bottlehead kit so my experience and knowledge aren't extensive...but this one is kicking my a** for some reason !

 

[Paul Birkeland]

Either fuse isn't good, it's in the wrong spot, the power switch is off, the power switch is melted, or the power cord isn't pushed in all the way (or not plugged in, I've done that more than I'd like to admit).

 

[nipsy]

Thanks a million for helping me to troubleshoot this, Paul !

I'm happy to report that I've passed all the tests up to the Audio Circuit and Passive RIAA wiring stage.

The issue turned out to be the cord. For some reason, it wouldn't push in all the way and so it was making a clean connection. I swapped in a different cord the pushed all the way in and everything checked out perfectly within spec. The cord that came with the kit didn't fit easily into the power module on the amp I took it from, but with some jiggling it got it to work.

I'm really happy that the problem was something simple and not entirely a failure of technique.

Seems like it might be time to upgrade my cord game !  On to the next steps !