Shunt regulator voltage problem

[Mid-Ranger]

Getting a low reading on the 431 regulator on the side in question......could that be it?

[Paul Birkeland]

What's the reading you see?

[Mid-Ranger]

The 2 outer legs show .825 resistance the middle leg measures .001

[Mid-Ranger]

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?

[Paul Birkeland]

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

[Mid-Ranger]

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! 

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

[Mid-Ranger]

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.

[Mid-Ranger]

Out of curiosity, one of the 220ohm resistors might have been shorting to a neighboring tube pin, could that have caused the voltage drop?

[Paul Birkeland]

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