Author Topic: Vintage Heathkit AD-1013 Audio Oscilloscope, test points way off  (Read 335 times)

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Offline cincinTopic starter

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I'm troubleshooting an old Heathkit AD-1013 Audio Oscilloscope that's behaving oddly. It's a pretty simple circuit and I have the Assembly Manual, which is very thorough, still I'm such a beginner I can't quite figure out what's happening...

In the attached schematics for the Vertical Amplifier part of the scope, test point 3 (TP3) at the collector of Q107 should be at +130V.
It's connected to the +200V rail (actually +193V) through R115 (15K) which is known good.

TP3 reads +193V, how can that be?

thanks!
 

Offline WattsThat

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Re: Vintage Heathkit AD-1013 Audio Oscilloscope, test points way off
« Reply #1 on: March 11, 2023, 06:28:46 am »
No current in Q107? It was common for those output transistors to fail open and the beam to be hard off center.

Visually check everything first. Soldering especially so. Then the resistors, the old carbon comps rise in value with age.

 
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