I know, we already have many 732 threads. Yet, I don't remember anyone talking about popcorn noise issue in them as of today.
Well, there is place for everything, so couldn't resist recent lures, and bought one of those 699$ sick 732A's.
Box arrived yesterday, and quick check revealed poor darlington on AC mains board cooking to +130 °C.
Quick swap with TIP122 (original is lower voltage TIP120) fixed that issue, so I hooked the output to some random meters:
After a day of runtime, I observe "popcorn spikes" on the 10V output , and buried in the noise 1.018V output.
Yes, I am sure it is not the 3458A (meter used for 10V 732A log.
Jumps are random, at -0.4 ppm level.
Guess I am looking at replacing SZA263 reference chip with a replacement? Anybody else here have this failure mode in their 732 unit, to share the experience?
Reminds my
jumpy LTZ1000A chip, which I still have somewhere.
I have 8842A for donor parts, so probably least resistance path is to steal SZA chip from it and put into this 732A. Of course I'll have to test SZA in 8842A first, to make sure that one is quiet.
Also will replace all electrolytic capacitors in 732A, but I doubt those can cause the noise like this.