[Techtoolslist] 9100 probe calibration

[Ian Eure]

I’ve been trying to calibrate my 9100 probe, and am running into problems.  I’ve tried two 9100s, two probes, two scopes, and haven’t been able to replicate what the service manual says I should see.

The manual says to hook the probe tip to the external trigger, and ground to the mainframe chassis; then, a scope probe to the cal out test loop and ground to the common test loop.  When this is done (and you start probe comp cal from the operator’s keypad), you’re supposed to see a square wave on the scope, which you can adjust with the comp trimpot.

On my main FT setup, I I’m just getting noise on the cal out loop:

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I thought the probe offset might be a problem, so I calibrated that with the service disk, but it didn’t help.

The second setup is a 9100A, and I get different (but also unhelpful) results.  I’m able to get a square wave, but it’s extremely noisy:

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I also tried setting the probe offset on this machine.  Even though I’m using the same service disk (V6), the procedure is different.  I guess part of it is in the system ROM.  The FT prompts you to connect the probe tip/ground to a 1.5V battery, enter the voltage, then reverse them.  The A procedure asks for a “filtered reference voltage between 1.0 and 2.0 volts.”  I used the same battery there, since my bench power supply doesn’t go down to 1.5V.  It’s not clear if I’m supposed to leave the probe connected through the procedure, and it doesn’t prompt to reverse the leads like the FT.  I get warnings about noisy transitions on the 9100A, no matter if the battery remains connected or not.

I’m peeling this onion because when I went to calibrate the pod to sync for my UUT, I got intermittent results.  And I calibrated that because I was getting some intermittent readings taking signatures off a good board.

Both mainframes and probes pass selftest, and appear to work in the gross sense of recognizing high/low/invalid states, counting clock frequencies, etc.

Anyone successfully completed this procedure?