cranky HP95


I have an HP95 calculator which has lost it. As long as the machine is not asked to perform with the tape in operation everything is fine. The minute the tape is put into operation by sliding the trace switch to the middle or far right position, the display freezes with a negative entry and the tape does not either print or advance.

Can anyone help?

David C. du Four


Do you mean an HP95C? The really rare one?

I have repaired one (I don't own one, I hasten to add), and I have a reverse-engineered schematic (available, as ever, from HPCC).

My hope is that your problem is power-supply related. I assume you have a known-good battery pack in there (The 95C has the same protection circuit as the other topcats, but like other topcats, it only works when the machine is on. The 95C would therefore seem to suffer from the same RAM-killing problem as the 25C and 33C, etc). It might be something as simple as a dried-up capacitor

A worse possibility, of course, is ROM problems (if the printer driver code is screwed up, then the processor could go crazy when it tries to use the printer). The bad news is that these ROMs were only used in the95C, so finding replacements is impossible.

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