OT - recharging NiCad in a Commodore SR4190


HI, sorry for OT-ness, but you may like to help me.

I recently resoldered new NiCads in my old Commodore SR4190, and it works OK.

However, I remarked that the wires going to the external recharging plug are directly connected to the ends of the 3-element NiCads in series.

My question is : how do I recharge these batteries without frying the internals (of course I'll switch the machine off, but is that enough ? and BTW can it work while connected to mains ?).

In other terms, what kind of voltage shall I apply to this machine to recharge batteries ?

I am thinking of adding a diode to prevent silly connections in the future, as I'll go without the original charger (safely "stored" "somewhere"...).

Thanks for any hints.


Ich have a SR4190R with a self made adaptor. I can have a look for the specs but I think something ist wrong with the wiring of your Como. Mine has a voltage regulator between connector, batteries and calc (look here)


Sorry, forgot to answer this:

[...] and BTW can it work while connected to mains ?
Yes, consult the manual which is somewhere on the net. But again, you may have a modified calc.


Thanks a lot,I'll hunt the manual on the Web.

I'm positive I have changed nothing regarding the wiring inside, but the batteries there were 3 red plastic with no markings, could be not original with a modification done by the previous owner. Alas the picture on the site you cite is not detailed enough.

It has the old voltage regulator but on the calc side, not the plug.

I'll exercise proper caution.


Thanks a lot,I'll hunt the manual on the Web.
I know I have it somewhere, please let me know if it isn't on the net anymore. BTW., my adaptor is unregulated, 6V at 120mA.


Hello, just ran into this :


There is stated that one can use 5 or 6V, positive tip (can check, I still have my screwdriver... and will put some low-cost diode to protect the innocent).

From typing on the beast I'm impressed with the look and it feels OK, I still have to figure all the probability functions.



There is stated that one can use 5 or 6V, positive tip
Positive tip is correct.
From typing on the beast I'm impressed with the look and it feels OK, I still have to figure all the probability functions.
It is a great machine function-wise, but suffers from too few registers. It has no algebraic precedence, only one level of parenthesis and just one storage register (actually two, but the second is used by many functions). In addition, most functions cannot be used in chain calculations and there are lots of little shortcomings like forbidden parenthesis in the exponent of y^x. Last not least, it is so slow, you would think you have a TI at hand!

The 9190 fixes most of these problems. Anyway, I always like to have the 4190 with me to calculate distributions.

Noteworthy are the gamma function, 2d statistics, the hms datatype and some other interesting bits. If it only had RPN... :-(

Edited: 2 Nov 2006, 1:18 p.m.


I have this on my site for pre-LCD electronic calculator manuals


Hi all,

I have 3 of these rather magnificent Commodore calculators with rechargeable batteries - an SR4190R, an SR9190R and an SR1400. They are all very impressive, subject to the limitations mentioned above.

However, when you replace the rechargeable batteries they ALL have a very serious problem - the power wires break off right at the end. I have just attempted to replace the apparently original batteries of the SR1400, which were very leaky, but failed because the negative battery wire broke off right at the mother board, presumably as a result of the corrosion from the battery. I have no idea how to prevent this and am unable to repair it once it happens. Exactly the same thing happened with the SR9190R.

The only machine whose batteries I successfully replaced was the SR4190R. On that machine, the mains power wire broke off at the socket, and I was able to solder it back on.

The only consolation is that it is apparently safe to operate them from an off-the-shelf variable power supply, set to about 4.5V. Do not use the original charger and do not attempt to blast them with too much voltage. The SR-1400 seems to be more sensitive and to require less power, possibly because it seems not to have a voltage regulator.



Yes I also had some problems with those wires, but as I was VERY EXTRA cautious, it didn't broke, but the metal would not accept solder very well, although there was no visible corrosion on this wire.

I don't understand what prevents you from resoldering on the motherboard, it's rather low-tech. If you want I could take a look and try to repair it(but I am in a faraway country). Or maybe others might chime in, it's just sad to let these nice calcs lay dead and helpless !

On the voltage regulator, the shape of that thing is really unusual (can be seen on the picture mentioned above). Probably hard to replace !

Katie, it seems your site is unreachable at the moment ? No worry, just to let you know in case. Thanks by the way...


They┬┤re not dead, they work off the external power supply.

As for soldering to the mother board, I'm basically just afraid of messing it up. I did once solder a new battery contact to the motherboard of a TI-58C and that worked fine, but in that case, it was a case of either "having a go" or having a dead calculator; i.e. there was nothing to lose. In the case of the Commodores, they do still work without the batteries.

Thanks for offering to help. What faraway country are you in?


Hello, I am in France. Glad to see you can manage it yourself.

I took some pictures but don't have a clue as to where to put them. This is no rocket science, so no big loss here (and I'm not really proud of this quick soldering job !!).

Actually I have an SR1400 waiting for new NiCads, I'll do it and report back, also other Commodores and of course HPs. For the HP, all it takes is cutting open the battery pack, much easier !!



Hello again, still OT...

I opened my SR1400 and found I have cut out the battery pack some time ago to avoid leakage (probably). So my question is : how many cells do I need ? On the back is stated taht it uses 6V, so my guess is 4 cells.

If anyone cares to confirm - I am soldering the stuff ASAP. BTW, no broken wire (yet).

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