How to fix Tek P5200 offset voltage problem

[thlee]

I used my Tek P5200 high voltage differential probe to test SMPS. I had found big offset voltage -9mV at 1/50 mode. If I changed to 1/500 mode, the offset voltage was less than -1mV. I tried to adjust R26 to minimize the offset voltage. Unfortunately, I couldn't adjust to 0 mV at 1/50 mode. The adjustment range of offset voltage was from -2mV to -15mV. When I had adjusted the offset voltage to -2mV at 1/50 mode, I measured offset voltage +6mV at 1/500 mode. Anybody have the calibration procedures of Tek P5200 HV probe? Or how to minimize offset voltage of both modes?

[tautech]

For the 5200A there's Combined User/Service manual on Teks website.
Part Number: 077053602.
~3.5 MB

You'll need to register to download it.

[thlee]

Thanks for your reply. I have download P5200A (Part Number: 077053602) manual from Tek website. The both HV probe designs are totally different. The labels and locations of the pots cannot match the P5200 so I cannot use for my calibration.

[mk_]

See attachments, not exactly the same probe but maybe a little help...

Michael

[tautech]

Thanks for your reply. I have download P5200A (Part Number: 077053602) manual from Tek website. The both HV probe designs are totally different. The labels and locations of the pots cannot match the P5200 so I cannot use for my calibration.

Send Tek Support an email asking for the Service manual for P5200.
They might want the SN# to confirm you have one so send that too.

[tautech]

This is typical of all manuals I can find for P5200.
While it's called a service manual there's bugger all in it for adjustments. 
https://www.tek.com/manual/p5200

[thlee]

Thank you all for giving invaluable information and advice to me. I have drawn the schematic diagram and uploaded it to anybody for their maintenance. In the first time, I made a mistake to have adjusted the R26 until I saw the reference schematic diagram from Michael. The function of R26 is set with the maximum output voltage Vo from the video Op Amp. Comparing with the P5200 and P5205 schematic diagrams, we found the pot for offset adjustment in the P5205 probe. I think the Tek. engineers also know the same problem.  After that product, all high voltage probes are added the offset pot to their products.