Bo-Lennart wrote:

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Have a SENNHEISER UPM 550-1 (audio level-meter). My problem is that
-14Vdc from the power-supply board is goes upp and down to nearly 0 Vdc.
If I take out the board labeled B15, the -14Vdc is stable. And I can use
the instrument as a AC-rms voltmeter. No problem. But something happen
the I re-plug the board B15. The B15-board have something to do with
the CCIR-filter (I guess).

But I need a service manual to find out.


** I doubt that it would be much use.

Some component pulling current from the -14V rail to ground on that PCB is drawing way too much. Likely culprits include zener diodes, bead tantalum electros and low voltage ceramic caps.
However, I would clean and inspect the board first; a loose screw, tiny solder blob or metal fragment would do the same thing if lodged in a bad place.

If you power the -14V from a bench supply, localised heating or a bit of smoke might direct your attention to the right area.



..... Phil