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At the risk of being the last one to figure this out, and at the risk of admitting I have a collection of TI programmables and calcs:

Last night I pulled out a TI-57 to play with. I had re-built the battery pack, but the circuits were corroded too badly (as they all are). It wouldn't hold a charge. I tried to convert it to a 9v battery, and it wouldn't work. Odd. It had worked briefly when the charger was plugged in. So, I hooked up a 9v supply... it still wouldn't work. Sooo... taking a "plunge" and doing something stupid, I hooked up the power backwards. Yep. It worked.

I then looked in my "box-o-broken-calculators". Two TI-55's. I'd messed with them awhile ago, as they looked as if they should work. I must have never considered hooking a positive supply to the black wire and a negative supply to the red wire. Too many years of following the convention and not wanting to burn out circuits. They both work. I'm even a bit surprised that I hadn't tried this before. I guess I follow the rules too much.

Anyway, if I hadn't figured it out, maybe there's someone else here on the Forum that can use this info and give it a try with calcs they had thrown in the junk box.

Long Live the HP of Old,
Michael

This probably means TI spent about 20 cents and installed a full wave bridge rectifier in series with the battery supply. No matter how you connect the battery, the proper polarity voltage is seen by the circuits. This was common when the calculator was worth more than the 20 cents it cost. The downside is that it imposes a constant 0.7 volt drop in the supply volt. Means it stops working sooner when on batteries, but it was probably so the power supply plug didn't have to be polarized.

Just my 2 cents worth (A decidedly NON-TI guy...)

??? I thought Mr. Meyer's message was that it does matter which way the battery is hooked up . . . Am I missing something?

I admit to having a non-functional TI-55, too -- I removed the leaky NiCads after I got it (sans charger). One might infer from my lack of ambition in getting the thing to work again that I'm a non-TI guy, too. But I've been playing with my TI-83+SE more than anything else, lately. (In fact, I may soon be selling my newest HP-42S to help pay for a guitar, but that's another story.)

Oops - TI questions here ?

The Charger of the TI-55 is indeed an AC-type - BUT: The battery pack contains two AA-sized NiCd batteries plus a DC/DC-converter to generate 9V.
You could easily replace these BP modules with a 9V battery.

Never forget: 0V is RED and 9V is BLACK or your calculaor is DEAD.

Find more in the www.datamath.org just search the TECHNICAL section and choose Battery Packs or Repair a Battery Pack.

Regards,
Joerg

Yest it's true the black wire is the positive and the red one is the negative. But TI calc don't worry about reverse polarity and if you plug the + to the red, it won't "grill" the calculator...

I agree. I hooked up all three "backwards", and all are working with the correct polarity. Normally it does "fry" circuits to connect them backwards, so it does appear to be a resilient circuit. But... What is Wrong With Those People to wire it backwards? Red is Red and Black is Black, and I don't think I've ever seen a device .... except one that is going to blow up in a movie.... wired any other way.

Incidentally: I have a collection of many early LED calcs, from all sorts of brands, including TI's and others, as many collectors do. They're cheap, unlike the HP's, which cost a pretty penny to buy. My HP's are my prized collection, of course.

I do think the competition from TI helped push HP to develop better calcs, but ultimately the mass-produced cheap products also contributed to the demise of the HP calculator. But TI wasn't the only culprit. And that's another story.

But the nerve! I never checked the TI 30's, etc., to see if their 9V connectors are even wired backwards....

Michael

on my ti 30 (ser # 8986077) the red is hooked up to the pos side of the 9v. good to hear from you dr mike. i thought you had given us up as incurable.

Yes... I am incurable. Unfortunately, "'tis the season" for people to do poorly, so I've been busy. Also, unfortunately, in my business, too busy can be bad. If people can't get in to see me for six weeks, they call after-hours with emergencies. And I'm not allowed to charge for calls....

I forgot to mention: I enjoy bringing calculators back to life, even if they're TI's. I enjoy the restoration of calcs, but I don't use them for my work. Sort of like my days as a bicycle mechanic. I enjoyed building and repairing more than riding....

Michael

Hi, Doc;

you'd rather be a psychiatrist alright; i.e., you already are! Substitute brains for bykes and calcs and you'll get to the point...

Best regards.

Yes, OLD TI calculator feels very cheep in hand but a vast majority of these LED calculators they done were still functionning these days, except some model with key bouncing.. They are "cracky" *except TI-58, 59 series)caculators but the electronic is as good as other brand. I have a lot of old TI and all are working good without prior rebuilt need. The newer graphing one ar not "cracky" calculator and the LCD, keyboard and electronic are good quality comparable to HP 48 or 49 series or even better physical quality with better reading display. Like i said, they lack a RPN scientific and a RPN graphing model to be at the top.

NO, NO, NO !!!!

OLD TI calculator feel very strong ! Let us define old. If you ever owned a TI-2500 Datamath or a SR-50, SR-51 - they feel very, very strong.

If you dismantle (like I did often) a SR-50 and a HP35 you won't find ANY difference in quality.
TI used that time tons of screws, gold platen contacts, rigid printed circuit boards - like HP did. Unfortunately there was a lot of really cheap competition like APF, Commodore, National Semi and some others and the price war started.

TI made a lot of steps to lower manufacturing costs and starting with the SR-50A/51A the product quality decreased. You know the TI-30 with the bouncing keyboard, the TI-55 II with the rusty contacts, unusable after some weeks of use...

But - they learned a lot - and they learned early enough:

The technology behind the TI-55 III (Far East replacement of the US TI-55 II)is more solid than a HP-30S.
A TI-89 has a better look-and-feel compared to ALL Sharp, Casio and even some (newer) HP graphing calculators.

Within some weeks I'll visit Thailand - the home country of Citizen brand. On my shopping list are some Citizen calculators, we discussed already here in the Forum that the HP9 series are rebadged Citizen's.(Side questions: WAS the HP9 EVER AVAILABLE IN US ????).

Later more - if you are interested.

If you need some info about the a.m. TI's - just visit www.datamath.org and search them.

Greetings from Germany, Joerg

Didn't TI invent the first calculator IC? And the cheapo TI's were all on one chip... pretty impressive, if you think about it. Don't get me wrong.... using the classic HP's is a religious experience for me..... I just plain couldn't afford an HP-67, so a TI-59 got me through college. And worked reliably enough.

Now I get to use the HP's I could only dream about. For me, that's the joy of this interest/obsession.

Michael

I was thinking about the cracky TI-55, TI-57, TI-MBA or TI-30, or the "one use" TI-55II. But the 30 serie is still functionning after all these years.

The TI-59 line and heavy 52 "smell" quality.

You are true, it depend of the meaning of "cheap". If it's "not costing a lot for what you get". TI-55 was less than 100$ and all i have here still works great after these years so it's cheap!!! ;-).

I mean "reliable" calculator instead. TI are reliable calculators, especially newer models. Casio, HP and Sharp newer's too but unknown for the majority of students. Now that these calculators are a lot programmable, i think all are about the same : I saw a program project for a TI-83 to 100% emulate the HP-48G!!!

Joerg,
Is it conceivable that some extra calculators from Thailand jump aboard your boat for other people interested here ?
I think especially of the impossible to find SPR400G.
Well, just an idea.
I'm also searching for a contact in Japan.
Greetings too

Just drop me a line at joerg@datamath.org.

Thanks, Joerg