Old TI SR-52

[Jonathan Pettibone]

Hello- I found an old TI SR-52 that I'd like to get up and running, but it's missing its AC adapter.  Datamath tells me its a 5.6v 200mA adapter, and I'm having trouble finding one new.  There seem to be a few of the original AC9130A model on eBay, but I'd just as soon get a new one.  Any chance of me finding one?  Also, will I need to referb the battery pack too? I don't care if it won't run without AC, but I'm guessing it needs a functional battery to run at all. Thanks!  

[Mike Barnes]

From someone who has refurbished lots of vintage TI calculators, my advice would be to get a compatible original charger from Ebay. I've gotten a few dead ones from there, but most run just fine. You have a number of choices in chargers: see Datamath ( http://www.datamath.org/BP_List.htm ) for details. I'm not aware of anyone making new ones. If you still have the original battery pack, you will need to refurbish it (they are usually corroded, and work poorly if they work at all). What I usually do is to carefully cut the two plastic strips on one side only and carefully lift the batteries out with the metal tabs, and replace the batteries with new solder-tail NiCads. Connect the battery contacts back up, then I usually put a piece of electrical tape over the cut end (or glue it-- I like contact cement as opposed to super glue/epoxy/plastic-glue  since the cut area is so small the cement holds fine, but can easily be pried up again the next time you need to replace the batteries). I always clean the battery pack contacts and calculator battery contacts with contact cleaner. Remove any corrosion you see anywhere, then put the battery pack back in and charge it up. Hopefully you will have good luck. One other piece of SR-52 advice-- I would not try running a card through the card reader to see it it works. Get the rest of the calculator running, then go do some web research on the SR-52 card reader. They are notoriously evil. I've repaired a couple, and you need to have all the information (and replacement wheels)  in hand before you start on that adventure. SR-59 readers are much easier to work on. Good luck! -- Mike

[Jonathan Pettibone]

Thanks for the tips.  I really just want to be able to do basic math as a curiosity/desk calculator. The chargers are cheap enough on eBay, so I don't mind rolling the dice on one or two.  I do still have the battery pack and the cells look good, but I do expect I'l have to try to replace them.  Some of the keys are stuck. I've gotten most of them to move, but the 0 key is still very stiff.  Thanks again! I'm just old enough to have done some of my statistics classes in Undergrad ('91-'95) using a mainframe, but we also had PC versions of the software available too.  This calculator fascinates me as early alternative to batch processing and mainframe dependence for simple statistical tasks.   

[Mike Barnes]

A couple of other points. In the SR-52, the charger charges the battery and the battery runs the calculator. The charger cannot run the calculator (and can potentially cause damage if run without the battery pack). So always be sure to have the battery pack in the calculator when attached to the charger. So when you get the charger, I would not expect any response from the calculator with the dead pack. You might try charging the pack for a couple of hours and then turn on the calculator briefly to see if you get any response. If you get nothing, change the batteries. Although my actual recommendation would be to change out the batteries first. Old NiCads are not a calculator's friend. Regarding the stuck buttons-- unlike today's devices, the SR-52 was designed to be repaired, not replaced in case of problems. It has screws and comes apart and goes back together again. There is a little more hassle with the SR-52, but not too much. The actual membrane keys should not be stuck. My experience with TI is that the membrane keys rarely get stuck (they more often generate multiple digits for a single keypress). More likely, someone spilled something sticky, or it's misaligned, or corroded-- in which case it would be best to give the plastic keys and membrane keys a look over and cleaning if needed. I just opened up the back of an SR-52 to review the process-- Take the 4 screws off the back, flip the back of the case to the right. You will then see the card reader with 5 screws. Remove the bottom 2 screws and the one in the middle (not the top 2 screws). The main circuit board can then be folded back to the left. You now have access to the keyboard and keys. The keys can come out, so be careful (take a photo before opening, or use Datamath to get keys back in the right places). In any case, you'll get a better idea of the problem as opposed to just bashing on the keys and hoping. Good luck! -- Mike