Here's a link to the instruction manual. http://www.wass.net/manuals/Melcor%20SC-635.pdf Note that it says to have the battery in place if you want to run it off the external ac adaptor. Sent from my iPhone On Jul 20, 2018, at 14:06, Brent Hilpert via cctalk <cctalk at classiccmp.org<mailto:cctalk at classiccmp.org>> wrote: On 2018-Jul-20, at 10:18 AM, Jules Richardson via cctalk wrote: Anyone got pinout/spec information for a MOS MCS2529? In particular, I'm curious about operating voltage. I acquired a Melcor SC-635 calculator yesterday and there seems to be some uncertainty about the output voltage of its (rechargeable) battery pack; some places say 2.4V, i.e. the pack is a pair of 1.2V cells, but others say 9V. 2.4V seems a little low to me for typical logic, but on the other hand I've seen a period ad which says that the external PSU was 9V - and so the rechargeable battery must have been somewhat less than that. Rechargeable and 1.2V/cell would correlate to 2 NiCd cells, a not-unusual configuration for calculators of that period. Such units would typically use a simple built-in switching power supply to boost the battery voltage up to levels adequate for the logic and/or display. In the pic of the PCB board here: http://www.teclas.org/maquina.php?mm=C125 the chunky box component 'below' the IC is probably a switching PS module. It was also common to use simple resistive current limiting in the charge circuit for NiCds. In consequence, the voltage supplied by the external AC charger may be quite a bit higher than the battery voltage. It's possible that's where the 9V external spec comes from, if not just a mistake. Sometimes the current limiting R is in the external charger, sometimes it's in the calculator. Further, such designs also tended to rely on the battery to provide AC filtering & voltage regulation (limiting) of the charger V down to the battery V. If the battery/cells have been removed or are in really bad condition, operating the calc from the original external charger can result in too high a voltage being applied to the electronics. My usual procedure for such calcs is to cut out the NiCd cells (there is ~0 probability they are any good), noting the polarity. For testing, clip on a bench supply to substitute for the batteries, set of course to the appropriate V for the battery ( # of cells * V/cell ). If the batteries have already been removed and there are no polarity markings, let me know if you'd like some assistance trying to figure it out. If you want to power it through the charger jack, then you need to assess whether there is any internal charging circuitry (rectification, aforementioned current-limiting R, etc.) sitting between the jack and the cells.

On 07/20/2018 10:57 PM, Tony Duell wrote: 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

On 07/22/2018 02:35 PM, Paul Berger via cctalk wrote: Oh, fun... so, I'd found this snippet of info online the other day: <<< I have this calculator that I purchased sometime in the 1970's. Just today I pulled it out of the desk drawer and took the back off to see what type of batteries it had. The only thing I had to go on was the number on the pack (12B012). I did a Google search and came up with zilch; however, I slipped the pack out of the cylinder case and did some measurements. It appears that two NiCad size 4/5A cells would work since the size is identical. You would need two of these single cells and simply slip them into the Melcor outer case (in series) then place them into the calculator. I have not tried this yet, but I do intend to try it when I can get my hands on the 4/5A cells. Size, voltage etc. seem to be identical. So I thought I was looking at a pack made from a pair of 1.2V cells. But I just revisited mine, also a 12B012, and realized that I could non-destructively dismantle it (I like keeping original batteries when I can - separate to the machine they were in, of course). Anyway *my* 12B012 is three cells, not the two that the above info seemed to imply. Somewhere I'd read that someone had powered one of these calcs up on 3V without damage, although it was a little temperamental. Deciding to risk that, I just tried it with a pair of 1.5V AA's and... it works! I still don't know the original voltage of the pack in mine, I mean maybe it was 3.6, maybe 4.5... but at least I can see how it goes now running on 3V, and make sure that the keys all work and such. cheers! Jules