I have an HP 7475A plotter (GPIB interface that seems to have a temperature
based fault. I have done some digging around on search engines looking for a
circuit, but have come up blank so far.

The problem is that it seems to loose track of pen position, or else senses
motor overcurrent on (presumably) the X axis. It is never consistent in when
the error occurs which also leads me to believe it is a temperature fault.
The motors appear to be DC ones with a quadrature optical encoder, so the
fault could be one output of an encoder, but the machine does not run for
very long before failing, making it almost impossible to service without
some circuit info.

The alternative is to come up with some GPIB to serial converter that we can
use to get hard copy of an instrument (an HP 3562A Dynamic Signal Analyser)
which has no other means of data access (Yeah, I know - great project for a
PIC!!).

any help appreciated.

TIA
Alan

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