"William Sommerwerck" wrote in
:

My LaserJet 4M has suddenly developed a serious problem -- just as I
need it to get out some important documents.

It's printing black lines across the width of the paper, about 1/8" to
1/4" wide. They occur randomly (two to three per page) and look as if
someone has run a Magic Marker across the document.

In one case where the line ran through a graphic I use on my
letterhead, the line appeared to be "behind" the graphic -- that is,
the white spaces in it were reproduced with little degradation.

This does not appear to be a toner-cartridge problem. It seems more
likely to be intermittent laser output. (When the laser is off, the
drum retains its charge and picks up toner that's then transferred to
the paper.)

I need this unit ASAP, and am willing to rip into it in the hopes that
the problem is a loose cable or failing solder joint. (I can download
the service manual for $7, if need be.)

Any ideas, anyone? Thanks in advance.



From service manual;

Table 7-17 Random Horizontal Black Lines

Possible Cause Action

Laser/Scanning Assembly Replace the Laser/Scanner Assembly.
misaligned or damaged.

DC Controller PCA Replace the DC Controller PCA.