Hi,
I bought a nice looking HP-334A from a well known auction site.
I had to replace the meter movement, as that was not working, so I bought another cheap unit for parts.
I have replaced all the electrolytics on the PSU and A2 board.
Calibration of the voltmeter was surprisingly easy, and it seems quite stable even on the 300uV range. Good enough for me anyhow.
I then went on to the next stage in calibration, the sensitivity level calibration.
On setting 5, I can set the meter to read 9mV at 400Hz fine. I then switch the oscillator to 100KHz and the meter bangs over on the end stop. Adjusting the little capacitor makes little or no difference. Changing the frequency to 1KHz, still the same, the meter bangs over hard past FSD. 400Hz it's fine.
I put an oscilloscope on the output of the impedance convertor and changed ranges and frequency and it looks quite flat.
Any help would be much appreciated. Where to look, what to test etc.
Best regards,
John
OK figured it out.
Don't try the calibration with the high pass filter switched in. Duhh.
So now I have a calibrated 334A.
Just need to change the electrolytics on the last PCB now.
John