Electronics > Repair
Tektronix TCP202 current probe repair - Schematic and suggestions needed
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esc:
Glad I found this thread.

I also have acquired a TCP202 in good condition. The probe "operates" but it doesn't "work".

I did test it with DC 1A and the display seems accurate. Also tested with DC 50mA and it seems accurate, but I need to degauss to go back to the original 0 value - after the DC 50mA test the trace is about 10mA higher then 0 every time. This may be normal, not sure.

The degauss works and so does the coarse zero (on the back of the probe head) and the fine 0 on the side of the plastic box at the BNC.

The sine wave in AC looks ok, but it is smaller than it should be. At 10KHz is about 15% smaller, at 20KHz is the worst, 60% smaller and it recovers at 40KHz to 15% again, staying around there to the MHz range. The square wave response is very ugly.

I measured the transformer in the head and I got the following values (compared to the previously posted measurements):
+3V - -3V = 276 ohm - 176 ohm
+3V - HALL1 = 183 ohm - 93 ohm
+3V - HALL2 = 179 ohm - 92 ohm
-3V - HALL1 = 189 ohm - 141 ohm
-3V - HALL2 = 182 ohm - 141 ohm
HALL1 - HALL2 = 110 ohm - 72 ohm
COIL - COIL = 6.5 ohm - 6.5 ohm

These are with the small PCB in the head disconnected. Are these still in range?

Also, the electronics in the plastic box looks good, no visibly fried parts, and no sign of any repair.

Attached some pictures. The load is a 100 ohm metal film resistor.
Any help would be greatly appreciated. Thanks.



 
esc:
Sine wave picture at 20KHz.
The two traces are supposed to be identical for the 100 ohm load (20mA/Div and 2V/Div).
esc:
One more at 10KHz.
Tantratron:

--- Quote from: MarkL on July 04, 2020, 08:12:19 pm ---
--- Quote from: Weston on July 03, 2020, 11:34:56 pm ---I don't think I ever explicitly check the square wave response on my TCP202 when I got it, so I am unsure if this is a new issue or an old issue, but I have realized the square current step response is quite bad on my probe. It almost seems like a HF/LF compensation issue, but there is no way to adjust that. Here is a waveform where I compare against at CT-2 current probe.
...

--- End quote ---
I have some non-flatness with my TCP202, similar to yours but not as extreme.

Do you have 50R termination on in the scope?  I never used an R&S scope, but I don't see an indication of the termination.  Or maybe using an external terminator?

--- End quote ---

You might remember that I did purchase few months ago a TCP202 to a eBay-Austrian but it was not working plus the jaw was partially broken so got lucky PayPal reimbursed me. This time, I finally acquired to Belgium a TCP202 along with a 1103 and P6243 where all work except the TCP202 would fail the compensation test on my TDS540C.

I've carefully balanced the DC offset after de the degauss, the TDS540C and the probe been running at least 20min. However there seems to be a response flatness issue, please see attached two pictures taken this morning.

What do you think and what would be the procedure to have a better flatness when 1KHz square current loop is sensed ?

I'm still on my learning curve of the TDS540C use and many options. Do you know if the probe compensation output of the TDS540C and the probe calibrator are standard or precision 500mV and 500 mA references ?

Thanks, Albert
Tantratron:
Earlier this morning, I thought to try leaving into open the probe jaw (see picture) and noticed then upon not easy or stable thumb pressure or slight movement the probe would display a flat square response. It is very unstable mechanically where the slightest movement would loose the correct response, then I did run the TDS540C probe compensation which this times shows a PASS status (see picture).

When I inspect visually the jaws, the external probe it seems quite neat so what failure or mechanical issue causes the probe to not work correctly when the jaws are CLOSED but the current-transformer with Hall sensor would tricky work when OPEN ?
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