| Electronics > Repair |
| Tektronix TCP202 current probe repair - Schematic and suggestions needed |
| << < (12/18) > >> |
| Tantratron:
--- Quote from: MarkL on October 13, 2020, 04:45:45 pm ---It seems odd that you would get a perfect waveform when the jaws are not locked CLOSED. In your photo of the disassembled probe, are you showing all the parts? There should be a coil spring inside a metal sleeve which forces the upper sliding piece forward, and there should also be a tiny ball bearing. The ball bearing is important. It puts pressure on the wavy piece of spring metal to make sure the sliding transformer piece is seated firmly against the lower transformer. It's also the thing that "clicks" when you move the lever to the CLOSED position. Does your probe click? Also make sure the wavy spring metal is in the correct orientation. Screen shot from the TCP202 Instruction Manual attached: spring metal thing (10), coil spring and sleeve (2) and (3), ball bearing (12). I'm pointing these out explicitly in case someone else before you lost them. You may not know they're supposed to be there. --- End quote --- Yes I did forgot to take pictures of the tiny ball, the spring assembly and metal sleeve... but there were there and later when re-assembling the probe head I did put them all together as shown in the service manual. Of course the initial issue was not resolved ! --- Quote from: MarkL on October 13, 2020, 05:08:00 pm --- --- Quote from: Tantratron on October 12, 2020, 03:09:01 pm ---P.S. regarding the tektronix 015-0672-50 calibrator 50 turns current loop, does anybody knows the schematics or circuit... does the calibrator really generates a super fast rise and fall 1KHz signal from the TDS front panel ? ... --- End quote --- Looking at the compensator output circuit I wouldn't call it "super fast", but it should be faster than what you're showing on the TCP202. It doesn't seem likely it's the calibrator output but you can verify it's shape with a voltage probe. Schematic snippet from http://w140.com/tekwiki/wiki/TDS540 --- End quote --- Today I've measured the resistive impedance and the inductive impedance of the tektronix calibrator, the values are 42 ohms and 85 microH so I really wondered if maybe the problem could be the calibrator speed (kind of slow 50 turns transformer). What you show is part of the TDS540C front panel circuit which generates the signal output whereas my concern is the external calibrator 015-0672-50 where the TCP202 will sense the current connected to the TDS540C. So later today I've built a quick and dirty test fixture, see the first picture where I connect the High Voltage output BNC of my PG506 to my Q&D box which is connected to a 50 ohm coax load. At the same time, I sense the voltage output to Ch 3 and display Ch2 the output of the TCP202. The good news now is that the TCP202 does respond very well with sharp rise and sharp fall at different 50% square signal (100Hz, 1KHz, 10KHz, 100KHz and 1MHz), see attached pictures. Then I've made a very high sampling rate to show the transient (see last attached picture) which is less than 10ns so this proves the probe works good BUT the problem seems to be a gain mismatch. I've tuned my PG506 to make 5V as shown on my TDS540C so if my 50 ohms load is precise I should get around 100mA but in average I get more circa 103mA or 104mA. As you see on the pictures, I've removed the top box of the TCP202 amplifier-compensator but I do not understand how to remove the bottom box. It seems to adjust the gain, one needs to access the bottom of the TCP202 box and maybe this will solve the problem. So either the TCP202 calibrator fixture is partially detuned or my TCP202 needs a gain adjustment to meet the PASS test of the TDS540C. It would be interesting to have someone post the circuit of the TCP202 to see if this makes sense or if someone could run its TCP202 with the 015-0672-50 calibrator to see the waveform, if if PASS or FAIL Thank you |
| MarkL:
--- Quote from: Tantratron on October 13, 2020, 06:58:43 pm ---... As you see on the pictures, I've removed the top box of the TCP202 amplifier-compensator but I do not understand how to remove the bottom box. It seems to adjust the gain, one needs to access the bottom of the TCP202 box and maybe this will solve the problem. ... --- End quote --- The bottom of the comp box is a friction fit. You can gently wiggle the black piece of plastic that is part of the BNC assembly out of the bottom. Then you can separate the two boards and undo the insulating tape around the bottom board as needed to get access to the pot. The coax going into the BNC is a Peltola connector and unplugs if needed. |
| Tantratron:
--- Quote from: MarkL on October 13, 2020, 10:40:40 pm --- --- Quote from: Tantratron on October 13, 2020, 06:58:43 pm ---... As you see on the pictures, I've removed the top box of the TCP202 amplifier-compensator but I do not understand how to remove the bottom box. It seems to adjust the gain, one needs to access the bottom of the TCP202 box and maybe this will solve the problem. ... --- End quote --- The bottom of the comp box is a friction fit. You can gently wiggle the black piece of plastic that is part of the BNC assembly out of the bottom. Then you can separate the two boards and undo the insulating tape around the bottom board as needed to get access to the pot. The coax going into the BNC is a Peltola connector and unplugs if needed. --- End quote --- I'm still not sure to properly understand how to safely access the gain adjustment part. I wonder if there is not a physical issue, see attached one picture showing my partial deconstruction of the compensation box. It seems unless I'm wrong that both half plastic covers have been mounted incorrectly or opposite when comparing to page 33 of TCP202 instruction manual. When removing the the top cover catches, I see directly the DC offset pot and the de-gauss button which should be the other way. How should I remove safely without any breaking both PCB's, how to unplug from the Tekprobe to re-assemble correctly the all unit ? What is wierd, the previous post https://www.eevblog.com/forum/repair/tektronix-tcp202-current-probe-repair-schematic-and-suggestions-needed/msg1663601/#msg1663601 shows an installation similar to my probe but does not corresponds to what tektronix instruction manual states... By the way, the page 33 does mention that the gain of the probe must be with +/-2% for the TDS oscilloscope compensation routine to work so I guess that was my initial issue (FAIL compensation routine) and not a flat response issue. |
| MarkL:
I'm not seeing the difference between your probe, the manual, and the previous photo you reference. It doesn't look opposite to me. Can you mark up the photo and point it out? Maybe I'm just being dense. Below is my comp box disassembled. The black plastic that forms the BNC assembly is just pushed into the bottom cover. It's a very tight fit, but it does come out. It is not glued or fastened by any other means. If you're working on the two boards, you can also unplug the Peltola connector to untangle the cables a bit. The white connector can also be unplugged, but it too is a tight fit. The brown piece of plastic in the photo is just insulating tape around the bottom board that can be undone partially as I've done, or remove it if you want. Just make sure you put it back. But I think you should be able to get to the gain pot without removing the bottom anyway by pushing the top board out of the way. You can probably shove the insulating tape to one side or poke a small hole in it to get to the pot. |
| Tantratron:
Hi Mark, many thanks for the guidance where now I've fully de-constructed the compensation box, cut part of the insulating tape to access the gain potentiometer per guidance. As you can see on the 2 pictures, my PG506 with my homemade current loop 50 ohms fixture along with the TCP202 trimming pot got it to a better gain calibration. Not perfect as a real test gear but then I've run the calibrator... the test is PASS plus we can finally see the calibrator was not supposed to generate an ultra-wide flat square (it is a 50 turns transformer). Again many thanks where I'm this time on the road to discover, use in my plasma test lab the TCP202 current probe versus my previous P6021 and P6022. Albert |
| Navigation |
| Message Index |
| Next page |
| Previous page |