Re: Sharp el-8

From: Rick Bensene - The Old Calculator Web Museum
Email: rickb@bensene.com


Greetings, The battery pack used in the EL-8 contains nothing but 6 standard AA-cell NiCd batteries. If you have the original battery pack, you can simply crack it open, pry out the old cells, clean it up inside, and replace them with new Nickel Cadmium rechargeable cells. Now...the problem is the charger. The charger for these machines had a poor design. It utilized a hybrid voltage regulator that was weak, and would frequently fail. This failure occurs on a great majority of the original chargers. Unfortunately, due to the high incidence of failure, finding these chargers in operational condition is very difficult. Sharp no longer supports any of these old machines, and doesn't offer any service parts. The charger is a bit special, in that it provides two voltages...9.6V and 7.2V, IIRC. The 7.2V is used when charging the calculator and the 9.6V is used run the calculator on AC power (MAINS position of power switch) The EL-8 has a dual-position power switch that reads MAINS and BATT, which switches the power supply according to the mode of operation. It is possible to build a power supply that emulates this, using a couple small 120V->12V transformer, a full-wave rectifier bridge, some decent filter capacitors, and a couple of programmable voltage regulators. I hope you find this information useful. Regards, Rick Bensene Curator, The Old Calculator Web Museum http://oldcalculatormuseum.com