First of all I'd recommend to remove all modules to make sure that the fault
is not caused by another module.

If you are a bit familiar with electronics you may alternatively disconnect
the bus boards from the power supply and look at the control LEDs of the
power supply.

If the -12V are still missing without anything connected the supply is
faulty. From your message I cannot see which power supply you have in use.
If it's an A-100PSU2 probably the -12V voltage regulator is defective. If
it's an A-100PSU3 the -15V module may be defective or the -12V voltage
regulator.

The following link to our website may be also helpful:

www.doepfer.com > English > FAQ > A-100 > My A-100 system does no longer
work

Best regards
Dieter Doepfer
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Doepfer Musikelektronik GmbH
Geigerstr. 13
82166 Graefelfing / Germany
registered in Munich/Germany, commercial registry HRB 97 399
CEO's: Sibille Heller, Dieter Doepfer
European VAT ID No. DE129329318
website: www.doepfer.com
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Best wishes
Dieter Doepfer

> Later on I noticed it was not only this module with strange
> behaviour...even some modules didn't even work anymore in that
> case.....so the final point is that I have no more minus 12
> Volt...! That's the reason for all.
> Anybody an idea what to do know
> Thanks,
> Danny