Bottlehead Forum

Bottlehead Kits => Eros Phono => Topic started by: Mid-Ranger on June 13, 2015, 03:09:47 PM

Title: Shunt regulator voltage problem
Post by: Mid-Ranger on June 13, 2015, 03:09:47 PM: I checked the voltage with the 12BH7 installed, all LEDs light up and the tube glows, but the voltage goes from over 300 and then drops to 100......

Any thoughts on what this could be or what I should look for?
Title: Re: Shunt regulator voltage problem
Post by: Paul Birkeland on June 13, 2015, 08:52:25 PM: What do you see on each Kreg? Can you post some photos of the board and its connections?

-PB
Title: Re: Shunt regulator voltage problem
Post by: Mid-Ranger on June 14, 2015, 03:05:49 AM: I get 4 for each kreg.... let me see if I can get some pics.
Title: Re: Shunt regulator voltage problem
Post by: Mid-Ranger on June 14, 2015, 03:15:24 AM: Pic
Title: Re: Shunt regulator voltage problem
Post by: Mid-Ranger on June 14, 2015, 08:16:14 AM: So can I go on with some of the rest of the build?

I hate to stop all progress.....
Title: Re: Shunt regulator voltage problem
Post by: Mid-Ranger on June 15, 2015, 04:11:00 AM: Ok like a noobie I forgot to check the other leg, so the wire from D7 measures 222v, it's the wire from D1 that drops to 100v.
Title: Re: Shunt regulator voltage problem
Post by: Paul Birkeland on June 15, 2015, 07:07:08 AM: Quote from: Mid-Ranger on June 15, 2015, 04:11:00 AM
Ok like a noobie I forgot to check the other leg, so the wire from D7 measures 222v, it's the wire from D1 that drops to 100v.

D7 should be grounded to the board through a 220 Ohm resistor. If D7 has appreciable voltage on it (more than 1V), either the resistor is broken, or there is a wiring error.

Do not proceed with the rest of the build until the regulated power supply is functioning.

-PB
Title: Re: Shunt regulator voltage problem
Post by: Mid-Ranger on June 15, 2015, 07:09:52 AM: Hi,

Sorry not D7, I meant the red wire from D6 has the proper voltage.
Title: Re: Shunt regulator voltage problem
Post by: Mid-Ranger on June 15, 2015, 07:11:50 AM: Could the tube be an issue?

Half of it not working?
Title: Re: Shunt regulator voltage problem
Post by: Paul Birkeland on June 15, 2015, 07:12:31 AM: Can you confirm that you have a 431 regulator on each side of the board and not an MPS4250A installed by accident.

-PB
Title: Re: Shunt regulator voltage problem
Post by: Mid-Ranger on June 15, 2015, 07:25:32 AM: Yep, 431 on both ends.
Title: Re: Shunt regulator voltage problem
Post by: Paul Birkeland on June 15, 2015, 08:04:43 AM: And 2N2907's in the middle? (not 2N2222's)
Title: Re: Shunt regulator voltage problem
Post by: Mid-Ranger on June 15, 2015, 08:18:11 AM: Yes, took me a while to finally be able to see the writing on the A side, but both are 2907.
Title: Re: Shunt regulator voltage problem
Post by: Mid-Ranger on June 15, 2015, 12:11:45 PM: Paul I have checked every single part on the shunt regulator board and confirmed them all.

Also went over the wiring for every tube pin on D socket.

I am attaching a closer pic of IB and I0.......could a solder bridge cause the voltage drop problem?

Charles
Title: Re: Shunt regulator voltage problem
Post by: Paul Birkeland on June 15, 2015, 01:54:18 PM: Quote from: Mid-Ranger on June 15, 2015, 12:11:45 PM
I am attaching a closer pic of IB and I0.......could a solder bridge cause the voltage drop problem?

I don't see a solder bridge between IB and OB, so no issues there.

Can you snap some photos of the bottom of the board?

Also, can you carefully measure the voltage on each side of the 2.49K resistor on the offending side?

-PB
Title: Re: Shunt regulator voltage problem
Post by: Mid-Ranger on June 15, 2015, 02:01:19 PM: Getting a low reading on the 431 regulator on the side in question......could that be it?
Title: Re: Shunt regulator voltage problem
Post by: Paul Birkeland on June 15, 2015, 08:06:18 PM: What's the reading you see?
Title: Re: Shunt regulator voltage problem
Post by: Mid-Ranger on June 15, 2015, 10:07:14 PM: The 2 outer legs show .825 resistance the middle leg measures .001
Title: Re: Shunt regulator voltage problem
Post by: Mid-Ranger on June 15, 2015, 10:13:08 PM: Just checked the other 431 and it measures differently.

I'm checking resistance with it still soldered in the board, should I remove it to check it properly?

And could a bad LM431 cause low voltage on one side?
Title: Re: Shunt regulator voltage problem
Post by: Paul Birkeland on June 16, 2015, 02:32:30 AM: Please check the voltage on each side of each 2.49K resistor.

Measuring resistance across a semiconductor won't really tell you anything unless it's completely shorted.

-PB
Title: Re: Shunt regulator voltage problem
Post by: Mid-Ranger on June 16, 2015, 05:18:29 AM: Ok I removed the board to get a pic of the bottom.

I will reflow the joints and reinstall the board and get the voltage reading, sorry I missed that in my zeal to get the board removed! :P

I will reflow socket D as well while I have the board off.

Here is the pic of the back side of the shunt regulator pcb.

Charles
Title: Re: Shunt regulator voltage problem
Post by: Mid-Ranger on June 17, 2015, 08:56:07 AM: Success!

Both D6 and D1 are now a stable 223v.

Removing the pcb allowed me to find my mistake of not soldering the drain wires from the STP to the center pin of D.
Title: Re: Shunt regulator voltage problem
Post by: Mid-Ranger on June 18, 2015, 04:34:05 AM: Out of curiosity, one of the 220ohm resistors might have been shorting to a neighboring tube pin, could that have caused the voltage drop?
Title: Re: Shunt regulator voltage problem
Post by: Paul Birkeland on June 18, 2015, 06:01:01 AM: Quote from: Mid-Ranger on June 18, 2015, 04:34:05 AM
Out of curiosity, one of the 220ohm resistors might have been shorting to a neighboring tube pin, could that have caused the voltage drop?

Hmm, maybe. If this did occur, the 220 Ohm resistor would pop if it hit one of the pins, and on the other side the supply for the 431 regulator would be grounded out, but you'd have a 0 biased 12BH7 forced to cook off 23mA, which would give you about 100V out of the regulator.

-PB