Hewlett Packard HP55 Calculator restoration

Restoration of a 1975 vintage HP-55 calculator. A good look inside this amazingly well built piece of technology. A short demo at the end.

[@noferblatz]

I got an HP 21 for my graduation present in 1975. Those guys made primo hardware. Loved reverse polish notation.

[@CalculatorObsessed]

Wow! That’s a real goodwill bargain.

[@Chopperdragon39]

my grandfather gave me his. it is unused, even the batteries are still wrapped in paper. but one's got leakage. once I understand more of technology I'll try to fix / clean it and eventually try to turn it on.

[@joshuanorris5860]

Do that :) Electronics is a great hobby. And i love to solder and fix things :) Its not so hard at all. To dabble in it

[@jmfa57]

Always cherish what your grandfather gave you! I wish you the best of luck getting it up and running. I am probably of your grandfather's vintage, I used HP-25, HP-45 and HP-67 calculators in my university years in the late 1970s, and I still use them. My own grandfather came from Sweden in 1903, and I still have the Omega wristwatch he wore, with the original box and receipt from 1952. When he passed, my late father wore it, and now, I occasionally wear it also. I've had a watchmaker overhaul it a couple of times to keep it in top shape, and whenever I wear it, Grandpa (Farfar in Swedish) and my dad are there with me. You'll never regret it. Too bad your grandfather never got to enjoy it, but I'm sure he loves the idea of you having it!

[@antraciet]

Good job !

[@cjflintstone9509]

Rob, congratulations on resurrecting that calculator! It's an awesome machine, I have one and use it daily. One correction to your video - the HP55 has 20 storage registers, R0~R9, and R.0~R.9. You access them via STO 0 to STO 9, or STO . 0 to STO . 9. So the program that wouldn't fit in memory should actually work if you use R0 instead of R.0. Check out the Museum of HP calculators, www.hpmuseum.org, for a wealth of information on this and other HP calculators. You can download an HP 55 manual, but it'll cost more than you paid for the calculator so it might not be worth it - but you'll learn some cool tricks this machine can do that you may not discover just by playing with it.

[@RobsFixitShop]

Thanks, It was an amazing piece of technology for the time and built like it was going into space. I later replaced one of the banks of leds that was misbehaving which was a little scary but went off without a hitch.

[@MrLionSp]

Good job ! Thanks!

[@trondsi]

Interesting video! Just added HP-55 to my collection. My "restoration" was much easier (but then I probably paid a bit more for it too). I swapped battery packs with another old HP, and to my surprise both now work better! (I got lucky there I guess). After some cleaning it now looks near mint. Very nice calculator.

[@RobsFixitShop]

Cool, I later replaced the bad display which wasn't too bad a job although I had read you shouldn't even try it.

[@hifijohn]

Very cool calc, it cost about $400 back then about $1800 by todays money.

[@diacenco.v5791]

Hi, yes, as I have seen vintage calculator collection, I have two HP Hewlett Packard 45 and HP 65, if you are interested?

[@juanpumarinorodriguez9925]

Hi, I couldn't see clearly in the video: were any of the key "domes" or switches cracked in your calculator? If so, do you know if they can be repaired? Thanks!

[@brentdaignault7565]

I have an HP 25 and the AC adapter. It runs on 2 AA nicad batteries that died a long time ago. The plastic battery case is part of the back but I was able to cut it apart and replace the batteries with ordinary alkalines. Runs great. The classic red leds are bright. One more thing - this model has an AC adapter that puts out 10.2 v AC, weird. We are used to adapters converting to DC. It's obviously charging the batteries and the batteries are supplying the power to the circuits. If you try to run it without the batteries installed, the display will light up randomly. It's probably not a good idea to do this. Also, with alkaline batteries, I won't be connecting the adapter at all. I might try nickel metal hydride AA but not leave it charging for too long.

[@GrahamNicholson56]

It's definitely not a good idea to run any Woodstock series calculator (HP-21, 22, 25, 25C, 27 or 29C) without the batteries installed or with a defective battery pack installed as the AC adapter is capable of blowing the ACT chip in the calculator. Many of these models advertised on eBay as "for parts" have this problem but it may be possible to resurrect them with a modern replacement ACT from Panamatik in Germany.

[@jmfa57]

@@GrahamNicholson56 I actually did this today, trying to recharge an older rebuilt battery pack. What started as an iffy calculator turned into a dead calculator in a day. Fortunately, I had another "parts" HP-25 courtesy of eBay, and the main circuit board was still good despite the keyboard circuit board being damaged, so I swapped boards, and now it runs again. I've heard good things about the Panamatik chip.

[@GrahamNicholson56]

@@jmfa57 What a pity, thank goodness you were able to retrieve the situation. I have used the Panamatik chip to repair a dead 29C I acquired from eBay; it works better than an original (faster, less power consumed, all standard programs built-in) but it is quite fiddly to install.