[hung]

Actually there was going to be no DC part at all. This happened by mere accident.

I was thinking a bit that if the calculator is theoretically the function generator on the examiner, there had to be a way to check it. So I decided just for curiosity to measure the DC activity to see if there would be any changes.
By logic, to check the calculator’s relation to the circuit, then I chose the best location to place the probes would be benneath it. So I inserted the negative probe, under pressure, between the adhesive tapes which glues it to the top cover. With the positive lead I touched the handle in a manner which also allowed me to hold the examiner in the regular way, just placing my index finger under it to avoid rotation.

It was impressive and totally unexpectable. With calculator on ‘zero’ DC milivotages showed some negative value. Then I entered random numbers. In the series of pictures bellow I entered 895 first, but this could be any value. It abruptly raised voltage. I looked at it with amazement. Then I added some more digits. The voltage went even higher. More amazement.
To make a long story short. As this wasn’t enough of and incredible and unusual behaviour, I found out that if I touched (not pressed) the numbered key pads, the voltages reversed rising and began to fall, as long as I kept touching the particular keypad. So, for instance, if I touched 6, voltages reversed direction and started to fall. When I released my finger, voltages started to rise again. Never heard of anything like that before. So what apparently the circuit is doing is ‘extracting’ electrical pulses from the calculator as a ‘galvanic effect’.

I used to own a Sony DMX mixing board which utilizes this principle. To write automation on it you had to actually touch the plastic faders which galvanically transmitted the info to the processor.

I reported this to RT and they could not achieve the same results as me with their meter. So they will be getting another one to check it. I decided to post this anyway.

And this is not the end. I also found that when I touched the zero keypad, the voltages would fall down but at a much slower rate compared to other keypad numbers which would fall faster.
**Note: I could only confirm this on the ICEL multimeter. I tried the same in another automatic brand and I could not repeat it. The voltages reversed as in the other model but not a slower rate as in the ICEL. So results may vary according to the type of multimeter used.

Anyway this deserves more time testing and time is one thing I don’t have much. So results may vary.

With very interesting and highly unusual results, I double checked my instrument to see if it was faulty or not. Everything normal in all checkups.

Next logical step was to check if this all could be reproduced with a calculator alone without the examiner. I have to my own use, a HP 6S model similar to the one glued to the examiner, so I did not need to unattach it.
I hooked the negative lead under it and no similar behaviour as above happened.