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Full Version: TI 2550III project, help me I can help you.
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Yes, I am aware this is an HP forum talking about equations way over my medically educated brain, and out of my checkbook's budget. I do, however, own a vintage TI 2550 III EC. It has been in storage for 30 years, perfect physical condition with original AC adapter and leather case.
I collect all kinds of vintage items from early Apple machines to coins to ivory to medical instruments etc etc. This calc has one obvious problem. The battery in the rechargeable pack has long since corroded, leaked, and dried up. I assume it does not even transfer current in it's shape. The calc will power on when plugged into AC power, with or without the rechargeable pack intact. The problem is, it will not function. The vacuum display works, shows what seems to be numbers, so I assume there is a logic problem as a result of the leak years ago. The board, all components, and all solder look to be intact. I don't see a reason the calc shouldn't function unless the the main chip is fried, which seems impossible due to it's location away from the battery. Should I attempt to replace the "AA" sized rechargeable battery in the pack to ensure even current?
The AC adapter is original 9130A rated at 5.6VAC@3W. Could too much current (5.6 not buffered by rechargeable pack to 1.2) create a short bad enough to damage components? I am not playing with it for this reason. If there is someone out here who wants to share some knowledge with me, I would love to hear it. This circuit is so simple I believe I could replace anything but the main MCP. Is this calc even worth messing with? I have tons of collectibles and love to wheel and deal and restore mainly clocks and watches. This is a new project. Any help could be rewarded. If this is a rare or valuable calc I would like to know. Also, if I should make an art project or stress reliever out of it that would also be valuable information. If someone want's to help me, I could return the favor by overhauling or repairing a broken mechanical watch, no matter the condition, or any clock or watch since the beginning of time. I have tools, parts, tons of stuff for swiss ETA and Rolex watches, my main hobby is playing Frankenstein with watch and clockworks that should have never run again. I enjoy challenges.
Somebody help me with this TI2550III and maybe I can offer some antique restoration as I am very good with precise mechanics and can fix any watch or clock known to man. Electronics make sense to me, but I need a helping hand pinpointing the possible short in this. Pics and phone number at request. Thanks, and I have read enough to believe there is someone on this very site who will laugh at this problem. Thanks.


I'd start by *at least* removing the battery pack, to prevent further damage. Don't operate the calculator without it as it probably provides both voltage regulation and some filtering. If you want to try troubleshooting, start with a new battery pack. (If you're in the US, a local "Batteries Plus" store can probably refurbish the pack for you.)

You might check out some of the general repair information in the Museum, like this one. Which is in the "Repairs" section There's also a short list of folks who repair calculators.

You might post a couple of photos in case someone want's to chime in with more specific suggestions. Welcome aboard!


Edited: 19 Oct 2012, 6:38 p.m.

The BP3 is a pretty empty battery pack - just the 1.2V NiCd battery, no electronics.
Please don't operate the calculator with the original power supply without a working BP3 installed. Before spending $$$ to refurbish the BP3: Connect a 1.5V battery directly to the two battery contacts of the calculators. Does it work?
Order a 1.2V 600mA NiCd with solder tabs and replace the old one...

Good luck.