Repair tektronix P5210 high voltage differential probe

[Tantratron]

I've bought from eBay a P5210 which unfortunately does not work properly, it does add strongly a 50Hz signal to the HF signal. I do possess another P5210 which works fine for long time so technically, I could side by side run them for eventually troubleshooting.

My first question, does P5210 or P5205 are reliable product or are they know to easily fail ?

My second question, it seems almost impossible to find the complete service manual of the P5210 on the internet except this recent post on EEVblog forum which offers the schematics of the P5205 probe https://www.eevblog.com/forum/testgear/tek-p5205-hv-differeantial-probe-teardown-btw-what-are-the-red-and-brown-wires/msg1225894/#msg1225894.

Last question, when I read the above https://www.eevblog.com/forum/testgear/tek-p5205-hv-differeantial-probe-teardown-btw-what-are-the-red-and-brown-wires/ thread (page 1 to page 3) which contains lot of information but also indicate not easy to repair, do you feel by return of experience if these P5210 or P5205 are worth the effort to invest their repair.

Thank you, Albert

[Hydron]

If you post some high resolution photos of the PCB (front and back) then it might help a lot getting answers.

[Tantratron]

Please find attached 5 pictures showing the deconstruction sequence including the PCB (top side and bottom side)

[Tantratron]

Hi guys,
Just for the interested parties here is R/E schematics from a P5205 (non A).
Best regards,
Bogdan

Special thanks to abulafia (Bogdan) on this other thread https://www.eevblog.com/forum/testgear/tek-p5205-hv-differeantial-probe-teardown-btw-what-are-the-red-and-brown-wires/msg1225894/#msg1225894 to provide the re-generated PCB circuit of the P5205 (attached again for the record). It would be nice to have the one of the P5210 which has partially same PCB even though we can see differences as well.

One thing which I still have not found, the way to calibrate, use the internal trimming in the P5210 or P5205 because no way to find a copy of the legacy tektronix P52xy service manual

[Tantratron]

Attached a higher definition of the PCB (top view).

However it would help to know the procedure to calibrate, namely the 4 capacitors to match the HV input divider then both potentiometer (big blue and small white at center) and finally both potentiometers on top.

The offset output calibration is easy where it consists of small screw on the output connector linked to the tektronix 1103 power supply

[Hydron]

The blue potentiometer and all four brown trim-pots will be for common mode adjustment. I would suggest leaving them along unless the common mode performance is bad after fixing any other issues with the probe.

If you do need to adjust them then I would suggest the following for adjusting the low frequency CMRR (blue pot):
- apply 50hz mains voltage common to both inputs
- use a scope with a good FFT function to look at the output at 50hz
- adjust blue potentiometer to get the lowest possible signal

This procedure has worked well for me in the past - by looking at the FFT of the AC input you avoid the need to worry about DC offset while adjusting the CMRR. It will need the unit to be working first though! The higher frequency compensation will be harder though, especially with a high voltage probe like this.

As for the circuit, it looks very similar to the p5205. I would use the schematic as a rough guide and compare your working unit to this one as you mentioned in the first post.

[Tantratron]

Thank Hydron for the CMRR blue top guidance.

Yes the P5210 seems similar circuit to the P5205 even though the P5210 has 9 chips IC, there are 2 x LM317 and 2 x LM337 regulated power supply. I did compare some parts like SMD resistors, capacitor and more or less the P5205 and P5210 are quite in accordance except some parts, again remember there are 9 chips IC on P5210 whereas the P5205 has only 7 chips IC.

About my need to fully calibrate the unit, since I've a good P5210 besides the P5210 which I've bought on eBay, I can side by side compare and my problem is the gain output requires some calibration. I've trimmed a bit the small white potentiometer right close from blue big potentiometer but i still have mismatch gain. I did check the actual high voltage with calibrated Philips PM9100-191 100X probe, they give same reading than the 1st PM5210.

Do you know the complete procedure to calibrate the gain of P5210 ?

On a side note, why is it so difficult to find the original complete P52xy service manual on internet ?

[mk_]

One thing which I still have not found, the way to calibrate, use the internal trimming in the P5210 or P5205 because no way to find a copy of the legacy tektronix P52xy service manual

Look for the Sapphire Instruments calibration-manuals (http://www.sapphire.com.tw/npproducts.htm), there you can see how to do this generaly...

those Diffprobes are all more or less the same: frequency compensated Voltage divider, some more or less advanced difference amplifier and finaly a bufferamplifier  with variable gain and variable offset.. if you have seen one you have seen them all ...

btw: the schematic for the 5205 seems not to different from the 5210 as the layouts for the signalpath look very similar.
The 5205 can bee seen here: https://www.eevblog.com/forum/testgear/tek-p5205-hv-differeantial-probe-teardown-btw-what-are-the-red-and-brown-wires/msg520841/#msg520841

[Hydron]

The small white pot should set the gain. How much different is it from where it should be, and does it seem to work otherwise?

If something is faulty then everything in the unit except the MAX436 should be replaceable if needed. Unfortunately the MAX436 IC has been obsolete for a long time, and it's a very unique and useful looking part

[Tantratron]

The closest gain reduction I can obtain through the small white pot occurs when its wiper is connected to the ground side. If the wiper goes up upper side towards resistor linking the output of MAX436CSD then the signal will increase making voltage calibration worse.

Even though both P5205 and P5210 circuit boards and schematics look similar, there are some difference as explained before.

The MAX436CSD receives power from U740 (LM317) and U850 (LM337) but there is some difference, my DMM reads +5.01V and -5,23V

The Burr Brown OPA603AU (amplifier) is installed on P5210 whereas it was an OPA698 (unitary amplifier). The other difference being that two more power supply chips, namely U840 (LM317) and U860 (LM337) to power the OPA603AU but there are again some difference, my DMM reads +9.87V and -10,18V.

So the question is how to calibrate with least effort and parts replacement the voltage gain which normally should be trimmed only through the small white pot unless there is a problem on the HV part, dividing network, MAX436CSD.

Thank you

[Tantratron]

P.S. I've attached scopeshots of both working calibrated P5210 (Ch 1) and the not-calibrated P5210 (Ch 2). Both are connected to an induction ballast with peak output +/-200V at 235 KHz where in one case, the white pot is at minimum value and other case at maximum value. The first P5210 was calibrated and also verified with another high voltage probe. The question concerns what part of the circuit would prevent the correct amplitude calibration and what would be least effort repair.

[Tantratron]

Hello All, not much progress has happened since 2018 except lately I do have now a TDS540C, a PG506 and found the P5210 manual on internet.

As opposed to my attempt to calibrate and/or repair the 2nd P5210 discussed in this thread backin 2018, the difference is that now I have connected per the instructions of the P5210 manual a 100V then 10V pulse generator at 1KHz. This time, I'm able thanks to the blue potentiometer mentioned by @Hydron have the same gain one each P5210. One P5210 was calibrated prior purchase in USA so it serves say as an etalon so now both CH1 and CH3 of the TDS540C receives each P5210 outputs (no need for the power supply tek 1103), each high voltage inputs of P5210 being connected to the single Standard Amplitude output fo my PG506.

As you can see now on the attached scope shots, wether 1000x mode or 100x each probe are within the tolerance at 1KHz.

However I notice on the partial un-calibrated P5210 there is an overshoot peak so I wonder first what part of the circuit could fix plus if this effect could not explain why at 250KHz sinusoidal I still cannot adjust the gain so both probes would roughly converge.

The key thing which is hard unless one of you have this information, the attached P5210 manual only explains what test to verify the integrity but does not have a specific service manual section explaining how to calibrate. I did try earlier connecting both P5210 probes to the 230Vac grid, the blue pot would sync each gains to be the same. However still the same problem if probing a 250KHz sinewave (I've used a 200W induction lamp ballast and bulb), namely pushing to its limit the blue pot there is no way to align same gain output.

Thank you, Albert