HP 4329A High Resistance meter teardown

[kj7e]

I've been waiting for one of these to show up in good condition for a reasonable price.  One popped up last week and I snagged it.  Looks to be in good shape and fully functional.  Best I can test (to 10GOhm) its well with in calibration.

Link to service manual;
https://doc.xdevs.com/doc/HP_Agilent_Keysight/HP%204329A%20Operation%20&%20Service.pdf

Link to member pa4tim's page;
http://www.pa4tim.nl/?p=2269

[Tomorokoshi]

With an oscilloscope, what does your Recorder output on the back look like? From the manual:
"RECORDER OUTPUT: 0 to 100mV analog output proportional to meter deflection. Output impedance is 1kOhm."

Is it DC or is there a lot of noise on it?

[exe]

Wow, what a beatiful piece of gear! I'd get one like this, but I'm afraid of being electrocuted by it.

[kj7e]

With an oscilloscope, what does your Recorder output on the back look like? From the manual:
"RECORDER OUTPUT: 0 to 100mV analog output proportional to meter deflection. Output impedance is 1kOhm."

Is it DC or is there a lot of noise on it?

Sorry for the late response, I just checked and there is lots of noise on the Recorder Output.  I suspect you found the same.

[kj7e]

Picked up a paper manual for cheap and just did the performance verification tests.  No need to touch it, works perfectly.  I pulled the power supply board and checked the electrolytics, one is a bit low, 22uF measures 16uF but all others are good.  About the highest resistance I can test right now is the 10GOhm input on my HP 3456A, which reads just over 10GOhm, the HiZ input on the Keysight 34465A reads about 8GOhm.  No idea what I'm going to use this for yet.

[Tomorokoshi]

With an oscilloscope, what does your Recorder output on the back look like? From the manual:
"RECORDER OUTPUT: 0 to 100mV analog output proportional to meter deflection. Output impedance is 1kOhm."

Is it DC or is there a lot of noise on it?

Sorry for the late response, I just checked and there is lots of noise on the Recorder Output.  I suspect you found the same.

Thanks for checking it. Yes, mine has the noise. I just found my notes. It appears to have a 2.3 kHz component to it. It doesn't seem correlated to either 60 Hz power or to the 100 kHz conversion oscillator circuit.

I was able to get fairly clean DC with a large electrolytic capacitor on the output terminals. The signal is basically the same that goes to the meter element. The mechanical momentum of it is able to damp out the noise.

Anyway, the electrolytic capacitor is not really the best solution for various reasons, and I was getting too deep in it for what I needed at the time. Eventually I will try to find a more elegant solution.