Bad readings on part 8 of the build

[Honeypot]

Hello everyone 

I reached part 8. Negative power supplies.

I carefully followed the instructions and did my best with soldering.

But my readings for pin 1 are way off -46v and -93v for pin 13.

I've been testing around and couldn't find the issue. I triple checked the components, but I couldn't find anything misplaced.

I may have done something wrong however...

Any help is appreciated 👍 

Thanks

[Never Mind]

I assume this is pin #1 of the positive grid voltage extension card you refer to.

1) This circuit uses +5v for a voltage reference so step one is check +5V is correct on one end of R28.

+5V needs to be very close for everything to work correctly. 

Let me know what you measure.

2) Next look for about 3.2V at AN5 PIC pin (8). This is the voltage feedback to the PIC AD converter that allow the PIC software to adjust the pulse width to control the -15V rail.

Let me know what you measure.

2.1) If the  AN5 PIC pin (8) voltage is correct then it is possible that R28 is low in value,  R26 is high in value or both are off in value.

Check the markings carefully and consider triple checking with a ohm meter.

3)  If the  AN5 PIC pin (8) voltage is NOT correct.

Check that the -46V you are seeing on the -15V rail also appears on one end of R26. If not check R26 soldering or for a possible board open track defect to R26 from -15V. (unlikely but possible)

3.1) Finally check for a possible solder short across R28.

Pin #13 at -93V is not off by a lot and this may be due to whatever the issue is with the -15V rail.

I would trouble shoot the -15 rail first and then if the -85V rail is still off go back and trouble shoot the -85V rail.

Do not leave it powered any longer than required to trouble shoot as C20 will be over voltage with a -46V on the -15V rail as C20 a 35V part will not take this over voltage for a long time before becoming damaged.

If you see the top of C20 looking a bit high (bulged) then it has been damaged and should be replaced after you get the -15V rail back to the correct value.

Good luck and let me know what you find.

Bob