HP-80 with bugs ... ?

[ThomasF]

Hi,

A while ago I received a HP-80 from Egypt. Frankly I can say that I have seen better preserved devices ...

When opened the device, some bug really fell out of the calculator, there were insects and eggs of different spices, but I managed to clean and restore it - and it springed back to life!

But, there is still some problem with it, maybe someone can give an hint of what might be going on ...

When I turn on the device, the display shows a random pattern, like the following (different each time I turn on the calculator):

Code:

3.3.3.1.6 .01.
0.0.0.00 0.0
0.0.0.0.0 44
- (just a single minus sign)
.3.3.3.4.1.  0
9.3.3.3.1.6 2 00
0.000
000.00.0.- #.#  (the dash is blinking and the # are a fast running number, like a stopwatch)

... and so on ...

Sometimes the last digit in the "mantissa" is "looping", ie. continously changing, but more often it is static.

The strange thing is that any keypress clears this state, i.e pressing CLx shows "0." and the calculator works as normal (or any other key - but the result is more unpredictable).

Sometime (more specific when a "running" digit is shown), the calculator is locked, and I have to turn it off and on again. And when on, it works like a charm until power off ...

So, something happens during startup, but only the display gets corrupt and the calculator works fine after clearing the display (and somtimes less frequently it stucks in a loop).

Any ideas what might cause this? Failing ROM (only at startup)? Bad capacitors which causes slow starting clock? ACT?

Cheers,
Thomas