Realtone SC-60 low battery display problem

[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 :

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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]
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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)