The Museum of HP Calculators

HP Forum Archive 11

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A tired hp45, tools, and a quiet night. (long)
Message #1 Posted by Jeremy on 16 Mar 2003, 10:19 p.m.

I'll start off by saying that if you've never taken and old hp apart, or if you don't have much electronics background, this might sound a little greek to you.

That said, I'd like to thank everyone for their support. As mentioned in my thread below, I bought a well-used hp45 on eBay for $42 or so. The seller said that everything worked, but that you had to push some of the buttons pretty hard. It didn't include a battery, manual, case, or any other fluff. But that is why I got it for so cheap.

So I asked some questions about the battery situation, and got some helpful replies. I decided not to go with a cordless phone battery pack, because then, I would also have to buy a suitable charger, and that kind of defeats the point of the whole adventure for me. So I went to Radio Shack and considered my options for about an hour. They didn't have a 3 AA or AAA holder. I decided that the AA holder was too thick anyhow. So I wound up buying two 2 AAA holders, with plans to meld them together.

Next, I got home and took the '45 apart. As I had read somewhere, I discovered that old HPs are a dream to work on. The chassis' are screwed together instead of using cheezy sonic welding. In fact, there were 6 screws and no latches to figure out! Nice. I got into the circuit boards, and found that they were screwed down to the front chassis piece. Again, no latches or anything cheezy. My next pleasant surprise was that the PCB with the circuitry on it was held to the contact board by friction pins. (I don't know if that is the official word..) Nice work!

On to business. I followed the wires, just to be sure the battery reference page on this site was correct, and naturally, it was. Now a good plan was forming in my head. I wired the separate 2-AAA holders together in series. (see photo links, below) The last bay of one holder was sacrificed, and I brought the lead out from there. With my trusty rotary tool and cutoff wheel, I made a couple of small cuts. One for each wire to escape the battery compartment, and one in the side of the circuit board for the positive wire to route through. The two battery holders wouldn't quite fit into the compartment, width-wise, so I had to fire up the old Dremel and cut the end off of one battery holders, so that they would fit side-by-side. Since my personal supply of Crazy Glue has dried up, I made do with a rubber band until work tomorrow. (where we have industrial strength Cyanocrylate glue)

So the final result is that I have an old HP45 that is not dependent on the dumb proprietary battery packs or anything resembling them. I can put rechargable AAAs or alkalines in it. Right now, it has a fully charged set of NiMH AAAs in it.

I got it back together and discovered that the shift key didn't work. So I took it apart and got a toothbrush soaked in 91% Isopropyl alcohol underneath the contacts a few times. I put it back together, and now the shift key worked, but the x>y/y>x key didn't work. So I took it apart and tried my best to clean under all of those little spring metal contacts as best I could. Now, the x>y/y>x key worked, but I had to press pretty hard on the shift key for IT to work now. C'est la Vie.

The caculator is together and 100% functional now and I'm a happy man. I do have to press pretty hard on some of the keys for them to register.

I kind of like the fact that this particular one has been used hard. The plastic of the enclosure has that nice worn feeling. The stippled surface on all the corners is worn smooth, and it feels like an old friend.

Just copy and paste the links below into a new browser window if you're interested in a tour...

Here's an overall shot of the front. (It looks much cleaner in person)

Here's a shot of the worn-out plastic barrier that goes between the keys and the spring metal contact strips. I replaced it with a piece of the wrapper from one of the battery holders. (shown next to it, left)

Here's the first shot of my jury-rigged battery pack:

Another view:

Here are a couple of shots of the new battery holders installed in the hp 45:

Here's a shot of what it looks like from the back with the battery door removed:

A shot of the triumphant display:

A shot of the Ikea nesting table I did all the work on, along with some of the tools.

Last but not least, time to celebrate!

Now, withing a few days, I should get the HP48G in the mail that I won from eBay over a week ago... X-(

Cheers! -Jeremy

Re: A tired hp45, tools, and a quiet night. (long)
Message #2 Posted by Michael Meyer on 16 Mar 2003, 10:34 p.m.,
in response to message #1 by Jeremy

Congratulations! The world is a better place, once again! Check out the posts on sanding the contacts. You'll be happier with error-free, reliable keys.

Thanks for sharing, Michael

I'm on the lookout for 1000 grit sandpaper. Thanks. (NM)
Message #3 Posted by Jeremy on 17 Mar 2003, 12:13 a.m.,
in response to message #2 by Michael Meyer

No Message

Re: A tired hp45, tools, and a quiet night. (long)
Message #4 Posted by Richard Parfitt on 17 Mar 2003, 5:38 a.m.,
in response to message #1 by Jeremy

Dont' use abrasive paper use small contact switch cleaning strips or what is know as blotting paper, soaked in iso-propyl-alcohol. Cut a small strip just wide enough to go under the metal humps. Grip each end with tweezers and get someone else to gently press down on the metal hump, then slid the strip backwards and forwards, it's bit fiddly but it works. This is a very gentle way to clean the contacts. I have done it on all my "classic" machines with no harmful effects. Regards Richard

Re: A tired hp45, tools, and a quiet night. (long)
Message #5 Posted by David Smith on 17 Mar 2003, 6:08 p.m.,
in response to message #1 by Jeremy

A piece of brown paper grocery bag soaked in alcohol ususally works very well for cleaning the switches. I use 1500 grit sandpaper. A single pull though on each side seems to clear up the worst of switches. I have checked its effect on gold plated PCB contacts and it does not damage them. I usually wet the sandpaper with a contact cleaner/conditioner like a Caig Gold Pen or Deoxit Pen.

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