HP laserjet 4m has suddenly stopped printing any text

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Hi, I've been using an HP laserjet 4M for many years, no problems at all. Used it yesyerday, no problems. Today, printer appears to work perfectly, no error messages, no flashing lights, accepts a job, pushes paper through the printer, no error, just perfect....except no text ! Self test OK, but no text. Print engine test OK but no 'stripes' on paper. I've changed the toner cartridge for a known working (but a bit smudgy) item, no text. Changed the fuser, no text. Cleaned the transfer roller, nothing. I've taken the printer covers off, nothing has fallen off, no wires obviously broken. I've even stripped the laser assembly and it's not even slightly dirty. The printer, although now 25 years old has only done 87420 pages. I've done a cold reset etc. I'm at a loss. Seems like either the laser isn't charging the drum, or the paper isn't charged, but surely there would be an error message? Any ideas?

[Imagecomputer]

Hi.

Check this out:  Pull out the cartridge.  There's a plastic part in there called the cartridge support. It's a black plastic piece that's clipped onto the top of the toner cartridge area.  The part number is RB1-2105-000CN.  I've also attached a photo.  

If that part has broken, or if it has become dislodged, it can cause the symptom you're describing.

Good luck!

Matt

Image Computer Corporation