MOS MCS2529 math chip

Paul Berger phb.hfx at
Sun Jul 22 14:35:00 CDT 2018

On 2018-07-22 4:17 PM, Jules Richardson via cctalk wrote:
> On 07/20/2018 10:57 PM, Tony Duell wrote:
>> It is not uncommon for the NiCd cells to act as a shunt regulator in 
>> such
>> calculators. The charger is of relatively high voltage (say around 
>> 9V), it is
>> applied to the cells through a current limiter (often just a simple 
>> resistor as
>> you say), and the fact that the on-charge voltage of the cells is 
>> perhaps 2.5V
>> (for a pair of NiCds) limits the voltage applied to the rest of the 
>> calculator.
> Thanks, all - that does seem to be the case here, supply via the 
> external jack just runs through a 39 ohm resistor and then hooks 
> straight to the +ve battery terminal, with no other 'magic' involved. 
> From there, the entire calculator is switched via the on/off switch on 
> the keypad, i.e. there's no standby power.
> The switch is good, and I've reseated the display and MOS IC, but 
> without any signs of life when feeding it 2.4V via the battery 
> terminals. The three electrolytics in it are all reading low on my 
> multimeter - I generally question the accuracy of that somewhat, but 
> as it's quick and easy (and they're over 40 years old) I'll probably 
> try replacing those.
> One thing possibly of note - while I strongly suspect that the 4-pin 
> Astec module is generating some necessary voltages from the battery, 
> the MOS MCS2529 and the pair of ITT 510-5N display ICs that are in the 
> machine both receive battery voltage to various pins (pin 28 on the 
> MOS and pins 1 and 16 on the ITT's). That makes me wonder if the 
> battery pack voltage isn't supposed to be higher (perhaps around the 
> 4.5V mark) - but obviously I'm reluctant to increase battery voltage 
> if there's actually some other fault that's preventing things from 
> working.
> cheers
> Jules
While I don't believe I have seen a calculator that uses that particular 
chip, I have seen the inside of a few Commodore calculators that of 
course use MOS chips and a pair of ITT510-5N display driver chips seem 
to be the usual for them.   My PR-100 have a small blue and white Astec 
module hanging on wires (AA4080 in my SR4190) in them that does indeed 
generate some other voltages used by the chips.  These calculators all 
have 3 NiCd cells in them if the batteries where already removed, you 
may get a clue from the shell how many cells it was designed for.


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