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Hard to find a fault looking at the waveforms except that the amplitude seems less when the key is pressed. I wouldn't have expected much change in that.

cheers

Tony
(04-08-2022 10:50 PM)teenix Wrote: [ -> ]Hard to find a fault looking at the waveforms except that the amplitude seems less when the key is pressed. I wouldn't have expected much change in that.

Is it interesting for you if I still show the pictures of all the other pins here? I have a total of 18 images. Pin 1 to 9 with a grid resolution of 1 ms and pin 1 to 9 with a grid resolution of 100 us.

Regards

Thomas
What could be of interest is to show a full display refresh, about 4mS, on the A segment from the ROM0 IC, one with key up and another with key down. Hopefully you can trigger the scope on the RCD pulse to the cathode driver.

cheers

Tony
Attached is a scope image from a HP-25.

Top is connected to the segA output of ROM0 showing a full display refresh with 77." on the display and the [7] key held down.

Bottom is connected to ACT pin 7 (key column 3) showing a full display refresh with the 7 key down.

cheers

Tony
Today I tried it again. However, the HP-25 hung up every time I connected the test lead to pin 7 of the ACT.

It then stopped responding to the keys and I had to turn it off and on again.

[attachment=10587]
Have made the following observations after the last procedure: The co-luminous A segments have disappeared! At least most of the time. Sometimes, however, they still glow briefly.

In addition, I noticed that many pins are bent and especially at the ACT I once had the impression that one of the pins was on another. Now I'm no longer the youngest and it may be that I bent them myself while handling. On the other hand, the problem was already there before my first intervention.

One pin, which I saw as being in contact with another, I bent away again with my finger. This was on the side of the ACT that was on the edge.
(04-11-2022 03:26 PM)Tom Flatterhand Wrote: [ -> ]Today I tried it again. However, the HP-25 hung up every time I connected the test lead to pin 7 of the ACT.

It then stopped responding to the keys and I had to turn it off and on again.

I have seen that happen also, but only seems to happen when I use a bench power supply with the scope. I have a small voltage selectable wall wart too and the same can happen.

There seems to be an interaction between my scope and a mains operated supply which I thought both would be isolated from each other.

This may stop if you have a 2.5V battery source for the power.

cheers

Tony
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