So, it's been s bit since my last update on the 2020B! The issue in my last post was caused by a bit of liquid trapped under the Silpad (from the IPA I used to clean the contacts with after soldering).
My parts came in from Digi-Key yesterday, so I put everything in last night.
New banana jacks and neon lamps.
Plus a new fuse holder to replace the one that broke during shipping!
So, I button everything up, plug it in, flip the switch and...problems. =(
If I set it to 1V, I get 1.5xx, with the x being constantly drifting digits. Anything higher than about 3V and it jumps straight up to 28V. The 10-20V range puts the output to 32V. Strangely, even though it seems out of regulation, I can still manipulate the last three digits with the dials (though it drifts up fast).
I have no idea what could possibly be wrong. Last time I checked the unit (3 days ago) it was working fine. I've only replaced what I mentioned above.
Something I did notice, Q4 is getting way too hot; it's at the point of burning your finger if touched. This is the transistor that powers the LM399's heater I think. I checked the voltage across the LM399's Zener pins and I'm getting 7.0028 volts, so that's in spec.
I wonder if Q4 is shorted, or if the heater is shorted even? Hmm.
Thoughts?
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