HP 7550A Plotter - Auto-feeder and paper eject issue

[Tony_G]

Hey All,

Just thought I'd post this here for anyone that went looking for answers on it.

I acquired a HP 7550A that was suffering from the auto-feeder failing to load paper. Opening the unit up didn't show anything obviously wrong and using the internal test routine (power the unit on while holding down the ENTER and 2 keys) showed that the photosensors were working as expected.

Digging around I found a page on the HP support website that talked about a different problem, the paper immediately ejecting after manual loading. The problem they claimed was that the sensors needed calibration and the suggested solution was to run the diagnostics routine.

This had no impact on my problem because I had already run it and nothing had changed but it led me to think about running the internal X-Y Motor Gain Calibration. The service manual says to run this after certain repairs so I thought, "why not give it a try" seeing that I might need to replace the motors anyway.

You run this by powering on the until while holding down the ENTER and 4 keys.

Well after a bit of motor back and forth, I tried the auto-feeder and it has now started working.

If you're suffering the same problem then this might be a helpful step in addressing the issue.

TonyG