Laserjet IIIp blank page problem - again.

[Charl]

Hello,

My Laserjet IIIp started printing out blank pages all of the sudden a
couple of weeks ago. It kept getting worse, and I decided to do
something about it. Research on the web learnt that this is a _very_
common problem with IIIPs.

I opened the printer up and ruled out a couple of causes: the laser
works, the mirror works, the logic board works, the fuser works, the
paper feeding mechanism works. This basically narrows it down to the
HV PSU. I'm pretty sure it didn't run out of toner since it did print
out some perfect pages while also spitting out tons of blanks a couple
of weeks ago.

A friend also had a broken IIIp. I replaced the main logic board, the
driving board and the PSU board with his, and the problem persisted.
Motor test also prints out a blank sheet (not a print test, which also
prints out a blank sheet, but the motor test using the button at the
back).

Any ideas on what I could do?

Regards,
- Charl

PS. This is obviously NOT a driver problem or anything computer
related - many people replied with suggestions to change computer
settings in past posts.