At 11:30 -0600 1/12/07, Mike wrote: The numbers so far are not totally inconsistent. The wart might supply 6.x V open-circuit or low-current, but rely on the battery pack to pull it down to 3.3V at 500 mA, running or charging. The circuit diagram on xgistor seems to indicate there's just a 4.7 Ohm resistor keeping the bus from being completely battery-limited. That said, the battery pack definitely contains 3 Ni-Cad cells, each typically around 1.1 or so V. (I have had mine apart, rebuilt with stock Ni-Cads, ond not fried anything.) Therefore 3.3 V to the electronics makes good sense. One thing I would *not* do would be to plug in the calculator without a good battery pack in place, based on the circuit diagram and on Tony's advice pertaining to the dire consequences of similar actions with HP calculators. FWIW, there is one more factor in the story. TI made a printer base (PC-100?) that you could place the calculator (TI-58, -58C, or -59) on to generate printouts. The method of connection was to take out the battery pack, and place the cavity that it just vacated over a protrusion on the face of the printer, which would then expand to lock the calculator into place. (There was also a compartment to put the battery pack into so it could charge while you printed.) Whatever the power supply in that doohickey was, it circumvented the battery completely. If anyone has one of those and could measure the voltage on its power pins, that would likely shed lots of light on what the calculator expects. (Sadly, mine went at a garage sale while I was away from home.) -- Mark Tapley, Dwarf Engineer (I haven't cleared my neighborhood) 210-379-4635 Dwarf Phone, 210-522-6025 Office Phone