My current project is very personal to me; it's an HP-97 calculator\computer which appears to be dead to the world. It takes a 6v AC input from an HP adaptor (which I've tested and is supplying current) which also recharges a built in 4.5v DC battery pack. I've tested both battery packs I have and neither are holding any charge. I'm led to believe this calculator will only work with the power adaptor IF a working battery pack is in place and will run just on a charged battery pack. I've ordered a new battery pack which should be here in 2 weeks time. I've decided to take an online course in Electronics in the hope I may be able to fault find these problems myself.
Are there any members living in Sheffield, UK please who might be able to help me troubleshoot this HP-97, I do have a PDF of the Service Manual which shows all the circuitry.
http://www.nightfallcrew.com/wp-content ... manual.pdf
From section 2.41 (battery charging) the presence of the installed batteries is necessary, and indeed the text states that the calculator will not function correctly without having them installed.
Looking at section 2-22, each of the seven 10 ohm resistors which form the printing head draw 500 mA (as a pulse) when a mark is to be made on the heat-sensitive paper. Therefore the highest peak will be drawn when the head is printing a vertical line - some 3.5A (possibly a bit less, because the head moves while printing, so the vertical line may be tilted a bit to the right) and this way of working will be specifically designed to allow a high current to be drawn from the batteries during printing, rather than trying to draw the printing current in full from the charger.
Presumably you have now received the replacement batteries and all is OK?
I've charged it and it maxs at about 5v DC.
With both the power adaptor and the battery pac installed I now get a single red dot on the LED screen which is new and I believe it to be the power charging light. No other keys do anything and I'm yet to get the red 0.00 screen
Obviously, if you have a faulty chip that may be the end of the matter - do you have enough test equipment (scope, function generator, etc?)