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Full Version: Can I use the hp45 display for HP55?
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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


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

Kind regards

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