Electronics > Repair
Tektronix TCP202 current probe repair - Schematic and suggestions needed
Weston:
That sucks that the probe you bought was a dud, best of luck in getting that resolved.
I bought a working TCP202 off ebay in good condition in the beginning of march for $450, its really weird how ebay prices have almost doubled since then, I wonder what causes such price trends.
From what I know, the read out is done via some standardized resistor value on one of the tekprobe pins. On the internet at large / eevblog forum there are tables of what resistor corresponds to what readout.
MarkL:
I'm sorry the purchase didn't work out for you. I'm sure there's one out there somewhere with your name on it.
The TCP202 has a 24C02 EEPROM in the compensation box which is read by the scope. I2C is used on the TekProbe II interface.
Probes with readout pins have a resistor that will set the scale multiplier, but I'm not aware of any values that will make Tek scopes change the units or termination to 50R.
Tantratron:
--- Quote from: MarkL on June 18, 2020, 03:06:58 pm ---The TCP202 has a 24C02 EEPROM in the compensation box which is read by the scope. I2C is used on the TekProbe II interface.
Probes with readout pins have a resistor that will set the scale multiplier, but I'm not aware of any values that will make Tek scopes change the units or termination to 50R.
--- End quote ---
Interesting to know that the TCP202 has a digital I2C serial bus to communicate between the probe part number and the digital scope. I guess same design (24C02 EEPROM with I2C bus) inside my high voltage differential probe P5210.
Would you have a document or datasheet which details the precise signal mapping of the TekProbe output pins, there 4 pins on the left and 3 pins on the right then the BNC connector (GND and signal) when inserting inside say my TDS540C front panel ?
MarkL:
--- Quote from: Tantratron on June 19, 2020, 02:26:59 pm ---...
Interesting to know that the TCP202 has a digital I2C serial bus to communicate between the probe part number and the digital scope. I guess same design (24C02 EEPROM with I2C bus) inside my high voltage differential probe P5210.
--- End quote ---
I have a P5205 and it does not have an EEPROM. The x50/x500 button changes the resistance on the "data" pin closest to the flange on the BNC collar. So, it changes the scale on the scope like the old-style probes. The 50x position is 1126R, but interestingly the probe needs power to set 676R for the 500x position. There must be a little bit of electronics involved with the readout pin.
--- Quote ---Would you have a document or datasheet which details the precise signal mapping of the TekProbe output pins, there 4 pins on the left and 3 pins on the right then the BNC connector (GND and signal) when inserting inside say my TDS540C front panel ?
--- End quote ---
It's an undocumented interface, but there's some info here:
http://w140.com/tekwiki/wiki/Tekprobe_BNC_connector
A better resolution version of the pinout is here, along with some info on the evolution of Tek connectors here:
https://download.tek.com/document/TekVPI.pdf
And someone has an adapter board with labeled pad functions:
https://www.eevblog.com/forum/circuit-studio/example-project-tektronix-tekprobe-adapterbreakout/msg1201386/#msg1201386
If you search around the net there's various reverse engineering projects.
I like TekProbeII probes because now that Tek's patent on it has expired (US4708661A), other major manufacturers are offering adapters to use Tek probes on their scopes. There's no need to re-buy all your expensive active Tek probes if you move to another scope manufacturer (well, minus the cost of the adapters).
Weston:
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.
This has to be a defect, right? No way this is acceptable behavior for a commercial probe. Given that the probe works down to DC the hall effect sensor is still good.
Right after degaussing before it jumps to the correct DC level the response looks more compensated. Could something have damaged the JFET that isolates the degaussing circuity from the amplifier? I have inspected the PCB and everything seems visually fine. I am pretty close to just replacing every IC on it that I can identify.
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