HP-97 display replacement
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06-30-2024, 07:31 PM
(This post was last modified: 06-30-2024 07:34 PM by Kees Bouw.)
Post: #1
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HP-97 display replacement
Hi all,
The time has come to start working on a very pretty HP-97 that I have, wonderful condition, probably hardly used. It has one problem: a missing display segment. Just one, the horizontal led in the middle of one of the characters. So I got a replacement display years ago but I don't know if is alright. Before I do the work of replacing the display I would like to verify that it is working correctly and that all segments light up. Is there any way to do that? I have the usual electronics equipment, including a scope, signal generator etc. Would be a shame if I replaced it and then found that it also has a missing segment, or worse. I have attached some pictures. Yes, I know there is a big scratch on the front, but I think I can polish that away, mostly. Kees. |
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06-30-2024, 07:54 PM
Post: #2
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RE: HP-97 display replacement
I never found the pinout of a Topcat display.
Why don‘t just swap and try it in your machine before investing time trying to check the spare display? Just give it a try, it‘s no so hard to replace |
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06-30-2024, 11:16 PM
(This post was last modified: 07-01-2024 12:16 AM by teenix.)
Post: #3
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RE: HP-97 display replacement
The 97 service manual has the pin out description of the display on the circuit diagram for the keyboard PCB.
You could use a 5VDC supply, connect each column in turn (marked as C1 - C14) to -ve via a flying lead, then using another flying lead connect the +ve via a 1K resistor one at a time to the LED anodes, (marked as SA- SG) Note that digits 1 and 13 on the 15 digit display only have a negative segment because they only ever light up as positive or negative (mantissa / exponent), all the other segments are physically missing. To make things simpler HP engineers only used 1 column to drive these negative signs hence there is no column 15. (same as on the HP-67) Column 12 is the common for the 2 negative signs. Mantissa sign is segment SE Exponent sign is segment SG I don't know if it applies to all Topcats, but removing the LED display module from its connector can be difficult because the single conductor wires are a tight fit. Too much wiggling trying to remove the ribbon cable can break the wires. cheers Tony |
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07-01-2024, 08:06 AM
Post: #4
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RE: HP-97 display replacement | |||
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