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Can I use the hp45 display for HP55? - Printable Version

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Can I use the hp45 display for HP55? - isanchez - 01-10-2014 03:07 PM

Dear friends,
I have a very nice HP55, but with one defective led segment. I also have a HP45 for parts.
I have realised that the display is divided in both cases in three sets of five leds (bubbles) each. Can I replace the defective set of five bubble-leds in the HP55 with a non-defective set coming from the HP45? I would like to confirm this with you before to proceed.

Thank you very much and kind regards


RE: Can I use the hp45 display for HP55? - Geoff Quickfall - 01-10-2014 06:40 PM


I used an hp 55 spare led block for transplant to an hp 45 which had a ghosting issue. I then took the 55 quartz crystal and put it in an hp 45 to increase the accuracy of the timing app on the 45.

Hp 80 discussion

Here is a copy from a while ago where I explained the swap.

Re: Heat staked keyboards with sticky, bouncy or corrosion present keyboard PCAs
Message #13 Posted by Geoff Quickfall on 15 Aug 2009, 7:55 p.m.,
in response to message #1 by Geoff Quickfall

I agree with the fault being in the LED block!

I have a 45 with a ghost problem and missing decimal point in the middle of the ghosting block.

Swapped with a spare 55 block and the decimal is back and the ghost gone.

Another salvaged 45!

Cheers, Geoff

RE: Can I use the hp45 display for HP55? - dramsey - 01-11-2014 05:35 PM

Yes, the LED displays (three 5-digit modules) are identical in all of the first generation machines (35, 45, 55, 65,67, 70, 80). I've replaced them myself.

You do need reasonable soldering skills. But heck, if I can do it...

One warning, although there's not much you can do about it: the brightness of the digits in each 5-digit module are matched, and HP matched the brightness of the modules used in each individual machine. It's possible-- likely, even-- that you won't get a perfect brightness match with the replacement module.

Also, before reassembling the calculator, take a little time to bend the legs on the newly installed module so that it lines up as well as you can make it with the existing modules.

RE: Can I use the hp45 display for HP55? - isanchez - 01-13-2014 09:05 AM

Thank you very much for your answers.
I shall go ahead with it.

Kind regards