HP-46 faulty keys - to Katie



#2

I've got an HP-46 which is in working condition except that some keys do not work at all. In some old forum threads I found a note from Katie that the cause might be a bad filter cap which might cause all sorts of weird behavior. Katie, can you confirm this?


#3

I definitely seen flaky printer output when there's bad filter capacitor, but I don't remember if I've seen flaky key functions in that case.


#4

Thanks for your quick response. Well, the printer works like a charm, but some keys on the left (SIN, COS, TAN, TO POL, X^2) don't respond at all. Too bad, it's in nice condition.


#5

According to the schematic, those keys are one complete electrical row (row 2) of the keyboard. I'd start by checking that there's continuity between the appropriate connections of the keyswitches and pin 8 of the Control&Timing IC. If not, check the keyboard DIL connector, cable, etc. If that's OK, I suspect the C&T IC itself.


#6

Thank you for your suggestion. I will try to isolate the problem. If the C&T IC is faulty I guess there's not much chance to repair it.


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