Electronics > Repair

Intermittent LeCroy PP002 probe autodetection pins

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pipe:
I just acquired a LeCroy 9354AL with three LeCroy PP002 probes (couldn't find the fourth). However, all the probes have a dodgy and unstable X1/X10 auto-detect which is annoying in this unit since the manual selection menu disappears if it believes it knows better.

The fault seems to lie in the probes themselves and not in the scope - they are even unstable when I measure the resistance between the pin and ground. Attached is a crappy photo for people who wonder which pin I'm talking about. Apparently I couldn't get the "Inline expandable thumbnail" to work.

I could just tape them over (or break them off! But I don't want to do that...) but I would much rather spend some time and effort trying to restore them. However, I can't find a way to get into these things, and before I break them by accident I wanted to check if you guys have any pointers.

I'd be interested in photos from dismantled probes, maybe a probe-specific service manual, or information about similar probes. I have of course spent some time searching for this but didn't even find information about the resistances required to identify, or if this some sort of standard.

shakalnokturn:
I haven't had the problem with any of my Lecroy probes but don't own any PP002.
On the PP006 a 1/10 probe, it's 11.1k between identification pin and shielding.
Before pulling it appart I'd try a drop of contact cleaner on the pin and between the BNC lock and outer conductor then spin them a little, including the pin.
Make sure not to get any cleaner in the compensation bloc.

tautech:

--- Quote from: shakalnokturn on December 07, 2021, 10:22:05 pm ---I haven't had the problem with any of my Lecroy probes but don't own any PP002.
On the PP006 a 1/10 probe, it's 11.1k between identification pin and shielding.
Before pulling it appart I'd try a drop of contact cleaner on the pin and between the BNC lock and outer conductor then spin them a little, including the pin.
Make sure not to get any cleaner in the compensation bloc.

--- End quote ---
This ^
OP, as a sanity check 10k between the sense ring and the BNC GND/outer should sense 10x at the scope. Generally there is some tolerance in the sense pin resistance.
Sometimes the sense rings can get tarnished and some rotates of the probe connector can help to polish them up for better/reliable sense pin contact.

pipe:

--- Quote from: shakalnokturn on December 07, 2021, 10:22:05 pm ---Before pulling it appart I'd try a drop of contact cleaner on the pin and between the BNC lock and outer conductor then spin them a little, including the pin.

--- End quote ---

Thanks, I tried this on one probe before I made this post, and it didn't seem to do much good. Now I tried that same probe again after repairing a knob on the front panel of the oscilloscope - and it now works perfectly! I guess it just needed some time to soak in.

I now did the same to my other probes and I was far more liberal with the solution this time, almost drenching the pin (and only the pin, careful with the compensation block as you say). It cured all my probes.

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