mike wrote:


but I have a long history of using one good system to try to fix
a bad one and ending up with two bad ones.

With those sorts of voltages running around, any kind of probing carries a
LOT of risks! So, you are wise.


I was also very surprised to see that ALL the banding had disappeared.
Both cartridges that had severe banding were now free from that banding.
I had cleaned the contacts and swapped cartridges dozens of time.
Now, it's all good! I didn't actually fix anything, so I'm expecting
it to fail again.

Well, you did mention a big toner spill. That stuff is conductive, and so
you have to get it nearly all cleaned up, or it will get in somewhere and
load down a corona supply. I'm guessing somewhere along the trail you
cleaned off the magic spot where the toner had shorted something out.


I'd still be interested in an explanation of how the banding
shown in the picture could possibly happen. I can't come up with
a failure mode that would produce such a varied banding pattern
on successive printouts of the same page.
Well, a weak corona voltage or dirty corona wire could give poor charge, so
the toner didn't all transfer to the paper. Then, the weak wiper blade
didn't clean the drum, so the toner accumulated as it rotated. But, I'm
just guessing. My experience has mostly been with the bad wiper blades.
Once the drum is covered in toner, the laser beam can't write the pattern of
charged and discharged areas, so the whole page comes out grey. But, you
may have actually had TWO problems going on at the same time, much harder to
diagnose.

Jon