Counting on the HP 5328B

[jrharley]

TGIF!, for those of us still doing a day job! 5328B progress to report.

We are now counting on the A input! Not without curious symptoms though. It does seem to be input level related at the moment. Shout out to Tony_G for the comment about that.
Attempting the first maintenance check, which specifies an input level of 25mV rms, doesn't kick it in. An input level of 150mV, does kick it in, and it starts counting............usually.

I don't have any feel whatsoever as to how miss-calibration might affect what I'm working through, but this thing HAS to be really out of whack. On a related note, I still need to get back to what appears to be a dead shorted trimmer cap on the A14 board. I'll examine it out of circuit and see what I can see. Hard for me to see how that's a good thing, so we'll see how we go with it.

It's not at all clear to me whether or not my solder re-flow blitz enabled this development, but I'll take it!
Photo of some magnified solder joints attached. - JRH

[jrharley]

A little TLC can go a long way! –

5328B update here.

I think we’re getting somewhere now. We’ve successfully passed the next maintenance check on channel A. All steps were spot on. 

Testing channel B went as expected as well, though it’s pretty clear things are out of cal. I'm pretty confident at this stage, that this beast is doing basically what it should do.

Service Note to anyone needing to work on the 5328B : Channels A & B have level controls, which are rotary potentiometers. At least they look and feel like pots. Fully counterclockwise on them is an indicator mark labeled “Preset”. It’s used in the maintenance check procedures. It is entered via a ganged switch on the pot, which is easy to miss if you’re testing with the knobs off. I had sourced some cheap test knobs for the project to avoid taking the original knobs on and off during the repair. Once I fitted those, I discovered the detent position. That development cleared things up considerably.

It looks like all this circuit needed was a little TLC. Now I can focus on getting the unit to the best place it can be for my situation, so, more to come……….JRH