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Replacement Ribbon Cable suggestions (HP 97 Calculator)

OtakuN3rd

Aug 18, 2018
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Hello all,

I am working on repairing an old HP 97 calculator for a friend (date codes on the ICs are from 1977 in this one, making it a very early HP 97). This is a desktop calculator with a printer and magnetic strip reader for writing and saving programs.

I have run into a snag in that the ribbon cable that goes from the program strip reader to the circuit board has separated itself and is damaged beyond use. I attempted to save it with double-sided tape but it was of no use.
IMG_20180817_193822701.jpg IMG_20180817_193907564.jpg

Does anyone know of a suggestion for a replacement? Originality is not an extreme concern to the owner, so replacing the connectors would be fine if needed.

The original cable has 13 conductors and is about 2.5" long. There is one row with 13 connections. All connections are straight through.

So far the best I cam come up with is making a custom cable and replacing the connections on the PCBs with regular pin headers. Problem is that I can't seem to find a 13-pin header in mass production. I did find some 26-pin (13x2) connectors and considered using them, but wanted to ask for other opinions before ordering the parts.

Thank you!
 

(*steve*)

¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd
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Jan 21, 2010
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Have you tried hpmuseum org?

If both ends are plugged in like this, it should be possible to purchase a flat flex to replace this one.

What is vital right now is that you get good measurements of the existing interconnector.

Width, length of interconnector, length of exposed pads, width of pads, spacing between pads.

This may be an option.

If you Google for it, you should be able to find the HP-97 Service Manual. That should come in handy :)
 
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OtakuN3rd

Aug 18, 2018
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Hi Steve!

Thanks for the reply and the suggestions!

I measured the cable, and it is 2.54mm (0.1") pitch and 2.75" long. Unfortunately, the product you specified on Mouser is not available in that size. I have not been able to find much of anything in regards to appropriate cable in pitch and conductor count.

I have found the service manual, and the part number I need appears to be 8120-2301 but Google only comes back with the service manual itself, some irrelevant Amazon listings, and a supplier in Russia. eBay has no results for that part number, either :(

I suppose I can go ask over at HP Museum. I saw the site while doing research on the calculator, but didn't realize they had an active forum (the results I saw in my searches looked to all be very old, archived threads).

Again, thank you for the information!
 

Bluejets

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Last edited:

(*steve*)

¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd
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(the results I saw in my searches looked to all be very old, archived threads)

I suppose I should join up to the new forum. You may find posts from me in the old forums :)

Another important thing to know is if the connections are on the same side of the flat flex or the opposite sides. I'm not going to open up my HP97 to find out :)

I'd check out this if you need a custom solution. It describes all the measurements that are needed.

However, there are also PCB manufacturers who produce flexible PCBs that you may be able to use. See here.

I noticed on ebay there were some 0.1 in flex cables that had 16 to 20 connectors but were too long (here and here). It may be possible to cut these down to 13 connectors and to cut and splice them to make a shorter cable. I have no idea if there's room for extra cable in this area of the 97.
 

OtakuN3rd

Aug 18, 2018
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There is a bit of extra room in the cabinet, so I cold go up in lengths a bit without much issue.

(*steve*) said:
I noticed on ebay there were some 0.1 in flex cables that had 16 to 20 connectors but were too long (here and here). It may be possible to cut these down to 13 connectors and to cut and splice them to make a shorter cable. I have no idea if there's room for extra cable in this area of the 97.
Steve, the cables you suggested might work, but I can't seem to find them when I start from the US eBay site, nor can I find anything similar to it.

Bluejets said:
Maybe go to wire and change the sockets ??
This may work, Right now the best alternative I can come up with is using a 26 conductor cable with 2x13 pins on each side. and only connecting half of the cable connector.

https://www.ebay.com/itm/26-Pin-2x1...ch-26-wire-IDC-Flat-Ribbon-Cable/391775813554
https://www.ebay.com/itm/10pcs-Fema...-PCB-Through-Hole-Arduino-and-Pi/223105294950
https://www.ebay.com/itm/40pcs-2-54...-Cables-For-Arduino-Raspberry-pi/132497035879

Outside of the above, it looks like I would have to have a cable custom made, which, for a one-off project, likely wouldn't be cost-effective.

Thank you both for your research and suggestions!
 

(*steve*)

¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd
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Hard wiring it would be my last resort. You'll be working with old, delicate, and irreplaceable boards which are populated with devices that may not have the best static protection.

If the items I suggested ship to the US (you're in the US, right), then just order them off the foreign eBay sites. Your login will work just as well :)
 

OtakuN3rd

Aug 18, 2018
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Hard wiring it would be my last resort. You'll be working with old, delicate, and irreplaceable boards which are populated with devices that may not have the best static protection.

If the items I suggested ship to the US (you're in the US, right), then just order them off the foreign eBay sites. Your login will work just as well :)

Looks like they do ship to the US. I went ahead and ordered one of those. We'll see how it works out when it gets here. :)

Hard wiring is not an option for this cable due to how the calculator is assembled. There is a plastic mid piece that this cable passes through. I would have replaced the connectors on the PCBs to pin headers instead of the ones that it has now that slide into it.

Again, thank you so much for all your help and suggestions!
 

(*steve*)

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Please let us know how it turns out and possibly cross post to hpmuseum.org too.

There may be others who have (or will have) this problem, so knowing how viable this is will assist them.
 

OtakuN3rd

Aug 18, 2018
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Update:

The ribbon cable came in and I was able to cut its width to the correct size with a paper shear. The length was a bit longer than the original, but it was still short enough to fit without trouble. I'm waiting for some new Ni-Cd cells to come in and then should be able to complete the repairs of the calculator.

Thanks again for the help!
 
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