My HP LaserJet 4 all of a sudden started printing black over the whole
page. Beneath the black I can see that the image I'm printing is
transferred onto the page, but it is mostly obscured by the toner
stuck onto the page all over.

My (very limited) understanding is that this may be caused when the
corona wire doesn't properly charge the drum. Is this correct? Is it
something else?

Is this problem caused by a broken corona wire? Is the corona wire
part of the toner cartridge, and if so, will replacing the toner
cartridge fix the problem? Is there someplace else to look for a
broken or disconnected wire? Is there a possible fault in the circuit
that applies a charge to the corona wire?

This LaserJet 4 has been a faithful and reliable workhorse for about
15 years. I'd like to find the problem and fix it, if possible.

Can anyone give me some insights as to what might be the cause and
solution for this problem?

Thanks,
Juan

"Juan" wrote in message
...
My HP LaserJet 4 all of a sudden started printing black over the whole
page. Beneath the black I can see that the image I'm printing is
transferred onto the page, but it is mostly obscured by the toner
stuck onto the page all over.

My (very limited) understanding is that this may be caused when the
corona wire doesn't properly charge the drum. Is this correct? Is it
something else?

Is this problem caused by a broken corona wire? Is the corona wire
part of the toner cartridge, and if so, will replacing the toner
cartridge fix the problem? Is there someplace else to look for a
broken or disconnected wire? Is there a possible fault in the circuit
that applies a charge to the corona wire?

This LaserJet 4 has been a faithful and reliable workhorse for about
15 years. I'd like to find the problem and fix it, if possible.

Can anyone give me some insights as to what might be the cause and
solution for this problem?

Thanks,
Juan

Have a look he-
http://www.fixyourownprinter.com/search/forums?q=LJ4

Colin

I have a 4M that's over 15 years old; I hope it keeps working forever.
Wonderful product.

I had a similar problem several months ago with the sudden apparance of wide
horizontal black stripes across the page. You could see the text or graphics
"behind" them.

I assumed there was something wrong with the printer itself. * After some
slightly acrimonious arguing with an expert on the HP user site, I schlepped
the printer to a printer service shop who was kind enough to make a test
print with their cartridge.

No problems. There was nothing wrong with the printer.

I bought a new HP cartridge, and it's worked fine since.

I'm have a lot of experience service electronic equipment, but the 4M is not
a product I'd like to rip into. I'd recommend finding someone with a spare
cartridge to confirm just where the problem lies.

If it turns out the printer needs repair, you find it much less expensive
to buy a used, (supposedly) reconditioned one. They're all over the Web, for
cheap.

* Part of the reason was my assumption that the laser discharged the "white"
areas on the drum. Actually, it discharges the "black" parts of the image.