I'm attempting to get sound out of a TX-Sector and I am stuck at the Aux Power Supply.

I have an inductive amplifier used in phone circuits and I can verify audio at the output of the soundboard pin 9.

I can verify the signal at pin 2 of the aux board and should see an amplified signal at pin 4. Tracing it back I can see the unamplified signal at U1 pin 1 but no amplified signal at U1 pin 4.

The aux power supply is a new gulf pinball board.

Any advice what I should look at next?

Thanks

I'll mention that the power supply is new as well. I still need to do the ground mods

Hard to determine if I have the right voltages at the aux board. How can I verify the 12 VAC and -12 V?

This is a goldmine. Thank you!

ok getting somewhere.
My -12VDC at VR1 is -5.
I get 12 vac across CR1 and CR3
I have 13.5 VDC at the junction of CR2 and CR4 and the Same at R7

But only ~-4 @ the non banded side of VR1. Does this indicate VR1 is bad? Comparing VR1 in diode test on the new board is open and .7 on the old board.

I'll replace VR1 and give it a try.

BTW here is the section of the schematic for reference

Screen Shot 2020-06-14 at 8.22.01 AM (resized).jpg

Replaced VR1 and R4 and I can hear audio at R4 now

Video

Pulled pin 4 and connected to R4 and loud glorious sound.

Video

I'm going to rebuild the old board. I've had too many problems with this one.

I'm not naming the maker of this board. I have no idea what it's been through before it got here

replaced C3 on the aux power supply and back in business. I can't imagine what happened to a new board that would knock VR1 and R4 out of spec and make C3 a dead short.

On TX the aux supply is above the mpu next to the reset board. I don't think anything could reach it there.

I'm more surprised by C3 being shorted. If it was a manufacturing defect could it have damaged the resistor?

VR1 isn't in that circuit so who knows what happened to it.

It was definitely easier to manage that the aux power board is essentially 3 discreet circuits