Hughes and Kettner ATS 120A

[jvm]

H&K ATS120A oscillating when powered up. -15 volt supply is showing 0 volts. Replaced 7915 reg with no change. I can blow on the circuit board and change frequency of the oscillation. Anybody seen this one before?

[Jazz P Bass]

You must get the -15 volt rail back up & running.
Forget the oscillation, blowing on it.
With the regulator removed, what is the resistance to ground of the output pin pad? (it may be loaded down)
What is the voltage on the input pin pad?

[jvm]

Thanks, Jazz P Bass. With regulator removed, input voltage measures -22.5V and output pad is O ohms. Shorted IC likely?

[Jazz P Bass]

So pin 1 & pin 3 are at the same potential?
I try to stick to the page that I am on when troubleshooting.
So jumping to an IC as faulty is just that. A jump.
The power supply itself has to be verified.
Any component in between the 7915 ouput pin & the header pin marked -7.5V (including anything downstream that is attached to the -7.5V rail) is suspect.
Can the header be disconnected?
That would be a big help, as it would isolate the supply from anything downstream (like an IC )
It may very well be the zener diode.

[jvm]

Isolated -15V supply. Still at 0V. Found C1 shorted but was labeled as C2 on schematic. Thanks, Jazz P Bass for getting me to calm down and use my head!

[Enzo]

And a note: ICs can short intrnally and load down a supply rail, however, most ICs do not have any connection to ground. SO that actually points away from a shorted IC being responsible for 0 ohms to gro0und. Points more towards some bypass cap.

If the 7.5v rail were shorted to ground, you'd see 470 ohms to ground at the output of the 7915, not zero ohms.

I take it back, there are a couple ICs with a grounded input pin, but I still think an IC won't be grounding a rail.

The regulator has three parallel little tantalums. I hate tantalums, and instantly suspect them.

[Enzo]

And a note: ICs can short intrnally and load down a supply rail, however, most ICs do not have any connection to ground. SO that actually points away from a shorted IC being responsible for 0 ohms to gro0und. Points more towards some bypass cap.

If the 7.5v rail were shorted to ground, you'd see 470 ohms to ground at the output of the 7915, not zero ohms.

I take it back, there are a couple ICs with a grounded input pin, but I still think an IC won't be grounding a rail.

The regulator has three parallel little tantalums. I hate tantalums, and instantly suspect them.

[CHRISREWORK]

does anyone still have the schematics available getting a repair done to my ats 120 and they woul dbe a huge help... none of the above links work any longer. any help greatly appreciated. thanks

[jvm]

I have looked and can't find the schematic. I emailed H&K and they shot it right out to me. Hope this helps

[g1]

Here's the schematic:
ATS120 Service Docs.pdf

[CHRISREWORK]

thanks you very much!!! Greatly appreciated!!