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Looking for HP-97 LED display
11-16-2019, 08:42 PM
Post: #1
Looking for HP-97 LED display
Hi,

Recently I acquired a very pretty HP-97, with a late version pcb, and even a working printer. All nice and clean, it seems not to have been used much.
Sadly, one of the digits in the display has a missing segment. See the attached picture. If you have a spare parts HP-97 with a working display unit that has no missing segments, I would like to make an offer on the LED display. The display unit only, I am not interested in any other parts.
Thanks for helping me out!

Kind regards,

Kees.


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11-17-2019, 03:22 PM
Post: #2
RE: Looking for HP-97 LED display
Are you sure it is a bad LED module?

The "ribbon cable" is prone to corrosion where soldered to the pcb boards. I've repaired/replaced a couple of these. Fixing one right now on a HP-92.
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11-19-2019, 09:29 PM
Post: #3
RE: Looking for HP-97 LED display
(11-17-2019 03:22 PM)aj04062 Wrote:  Are you sure it is a bad LED module?

I'm pretty sure it is not a bad contact. Not one that can be repaired anyway. If one of the flatcable connections was faulty I would expect a whole row of identical segments to fail, not just one segment in one digit.

Kees.
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11-20-2019, 12:43 AM (This post was last modified: 11-20-2019 12:43 AM by aj04062.)
Post: #4
RE: Looking for HP-97 LED display
Nope. Not the way this display works. I guarantee it. I just repaired a 92 that would not display the negative signs prior to the number and exponent. When I had it apart, I saw under magnification that one of the ribbon cable connections was broken. As I worked on it, I broke a couple others and then entire digits started to drop out....

Once I removed the entire connection, stripped back the insulation (heat not knife) and re-soldered, everything was A-OKAY.

It may be the display, but check this first!

Adam
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11-20-2019, 04:42 AM (This post was last modified: 11-20-2019 04:50 AM by teenix.)
Post: #5
RE: Looking for HP-97 LED display
(11-19-2019 09:29 PM)Kees Bouw Wrote:  
(11-17-2019 03:22 PM)aj04062 Wrote:  Are you sure it is a bad LED module?

I'm pretty sure it is not a bad contact. Not one that can be repaired anyway. If one of the flatcable connections was faulty I would expect a whole row of identical segments to fail, not just one segment in one digit.

Kees.

You are correct. The single dead segment is most likely in the display and sadly I think it will be unrepairable. Still, although it might be a niggly problem to not work perfectly, it is the last mantissa digit and doesn't have to be used most of the time.

cheers

Tony
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11-20-2019, 04:46 AM (This post was last modified: 11-20-2019 04:51 AM by teenix.)
Post: #6
RE: Looking for HP-97 LED display
(11-20-2019 12:43 AM)aj04062 Wrote:  Nope. Not the way this display works. I guarantee it. I just repaired a 92 that would not display the negative signs prior to the number and exponent. When I had it apart, I saw under magnification that one of the ribbon cable connections was broken. As I worked on it, I broke a couple others and then entire digits started to drop out....

Once I removed the entire connection, stripped back the insulation (heat not knife) and re-soldered, everything was A-OKAY.

It may be the display, but check this first!

Adam

Actually the display does work in the manner described. Multiplexed common cathode.

The sign digits are common to the one cathode driver output which is why they both worked when you repaired the connection. The sign digit on these calculators only have the [G] segments fitted to the display board, which makes economic sense as all the other segments are not used, unless like me the display gets used for other purposes ;-)

cheers

Tony
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