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HP-25 Co-luminous segments
04-08-2022, 10:50 PM (This post was last modified: 04-08-2022 10:56 PM by teenix.)
Post: #21
RE: HP-25 Co-luminous segments
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
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04-09-2022, 06:58 AM
Post: #22
RE: HP-25 Co-luminous segments
(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
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04-09-2022, 09:22 PM
Post: #23
RE: HP-25 Co-luminous segments
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
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04-10-2022, 12:23 AM (This post was last modified: 04-10-2022 12:27 AM by teenix.)
Post: #24
RE: HP-25 Co-luminous segments
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


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04-11-2022, 03:26 PM
Post: #25
RE: HP-25 Co-luminous segments
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.

   
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04-11-2022, 06:37 PM (This post was last modified: 04-11-2022 06:51 PM by Tom Flatterhand.)
Post: #26
RE: HP-25 Co-luminous segments
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.
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04-11-2022, 06:40 PM
Post: #27
RE: HP-25 Co-luminous segments
(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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