Realtone SC-60 low battery display problem

[isanchez]

Hi,
I have been working in a Realtone SC-60, trying to put it in working condition. The thing is that it is working fine now, after solding a couple of wires and change a transistor.

To fully finish with it I would like to know if you can help me with this:

The calculator works fine, but it always shows the "low battery status" indicator. This is an "L" in the most left side LED character. I have replaced the rechargable batteries with fresh new ones, and they can be charged using a typical charger connected to the calculator without problem. I know it is not very important but I would like to repair it completely, and I have to confess it is a bit annoying...maybe there is something simple, you can tell me to do...

Thanks in advance.
kind regards and Merry Christmas

Ignacio

[Katie Wasserman]

There's probably a resistor or two that sets the low battery threshold. But without a schematic it could be hard to find this. I would run the calculator off an external power supply -- removing the nicad cells -- and see at what voltage point the indicator turns off. If it doesn't turn off by the time you get to a reasonable voltage (1.5 x number of nicad cells) it's probably something more than just a resistor tweak that's needed to fix this.

[isanchez]

Hi Katie,

thanks for your prompt answer. I shall try what you propose.
I found this calculator nearly for free. It is nice and looks very pretty on the table, but I have not found many information about it...so diagrams are impossible to find.

Again: thanks a lot.

Best wishes to all of you.

Kind regards

Ignacio

[Didier Lachieze]

(12-23-2014 08:21 AM)isanchez Wrote:  I found this calculator nearly for free. It is nice and looks very pretty on the table, but I have not found many information about it...so diagrams are impossible to find.

It's indeed a nice looking calculator.

As it includes three MOS chips (MCS2525-004, MCS2526-005, and MCS2526-004) the following seems to be related :

=====================================
Electronics - Volume 47 - Page 319 - 1974
New products Semiconductor
Third calculator chip adds power
Array lets scientific unit compute complex functions in a few keystrokes
Solving advanced mathematical, statistical, or scientific problems becomes elementary with any handheld scientific calculator designed around a new three-chip set from MOS Technology Inc. Basic calculating features plus a 14-digit display are handled by two chips, while the third extends the computational power of the system to include advanced functions.
Designated the Senior Scientist, the set operates in conjunction with a 40-key keyboard. On these keys, factorials, binomial coefficients, probability integrals and other advanced functions are represented in the "upper-case" position, actuated by a shift key.
All three chips are involved in handling series expansions, vector manipulation, permutations and combinations, coordinate conversions, complicated statistical equations, and complex mathematical problems in general. But the first two chips of the Senior Scientist may also be used alone to provide a basic 40-key scientific calculator.
This unusual option is provided by a system architecture common to all scientific-calculator array sets from MOS Technology: the master array of the system is programed to recognize the presence or absence of the third chip, and no electrical change is required to change the functional level. Included within the chips of the set are 12 data memories and 2,560 words of program storage. The memories are allocated in such a way that three are directly usable by the operator with separate store /recall keys. An additional four memories are internally accessed for storage of statistical group data, prior result data, and prior parentheses data. The remaining five are used by the system as working registers. A minimum number of external components is required for integration of the set into finished calculator designs, the company says, and power dissipation is kept at minimum levels, less than 300 milliwatts average. Price of the set is $50 in quantities of 100,000. MOS Technology Inc., Valley Forge Corporate Center, 950 Rittenhouse Rd., Norristown, Penn. 19401 [411]
=====================================

As well as this article including a detailed schematic: Build The 'Senior Scientist' Calculator, Popular Electronics, Oct. 1975, which describes how to build a calculator similar to the Melcor 655 which was sold as a kit.

You may also be interested by the following article: Build An Under-$90 Scientific Calculator, Popular Electronics, Jan. 1975, as it's a construction article for what looks like a Melcor SC-535 scientific calculator, a unit which uses two of the same MOS ICs (MCS2525 & MCS2526). In both articles the schematic and description show that the LowBat level can be adjusted with a variable resistor.

Here is a picture of the inside of my Melcor 535 (which I've still to restore), showing the small hole in the PCB to adjust the LowBat resistor R3:



Btw, can you post some pictures of your Realtone SC-60, including the electronics inside? It's always nice to see some of these early beasts.

(Edited to fix some typos and to add the Melcor 535 infos)

[isanchez]

Hi again,
Didier: very, very interesting information.

I have to say that my calculator is an ATAIO SC-6010, made in Japan...you gave me the clue it was a Realtone SC60...by answering to my previous post int his section (thanks!)...probably this model was rebranded by many companies.

I shall put some photos soon!. Externally looks like new...It comes to my mind the hp-45, when I look at it...the ATAIO has more statitics features. It is very solid and well done...Internally, well, it gave my some problems, as the batteries were leaked and the acid did it's job...now the only issue to solve is that the "low bat." indicator is always on....

I keep you informed of my progresses.

Kind regards
Ignacio

[isanchez]

Dear Didier,

you were right! I found this regulable resistor and as I moved it...the low bat display turned off!!!
Now the calculator looks and works fine thanks to your colaboration!

Thanks a lot!

Regards, and happy New Year!
Ignacio

PD: I still have to upload the promised pictures.

[Didier Lachieze]

Great!! Now waiting for your pictures ...

[isanchez]

Here:
https://www.dropbox.com/sc/39e7qaqpz3c9p...A5V4VVZvYa
some pictures...only external. I have to find time this week-end to open it...again!! I think I have opened it one thousand times these last days.

It is interesting to say that model 6010 differs from model 60, because it has 10 aditional storage memories, thus the added xx10. I also have added a newspaper ad with the explaination here: https://www.dropbox.com/s/pjtl5zzz72kqgj...1.jpg?dl=0


Kind regards

Ignacio