Laserjet 500 color m551 pages print yellow over entire page

[Whiskeyfoxtrot]

An old M551 was given to me that had streaks of yellow and magenta, so I cleaned everything I could and replaced the toner cartridges. The fuser was clean, the transport belt was really dirty with toner all over, so I followed online directions and cleaned it. Looked great when I put it back in! Then the yellow cartridge was hosed - yellow toner all over the place inside. Magenta was better than the yellow, also messed up but not leaking toner all over. Black and Cyan were fine. Cleaned all that up and replaced all the cartridges. Made sure firmware and software were all updated.

The test print has yellow over the entire page so it looks like the page was printed on yellow paper (pretty much). The transport belt and the little roller on the right door are now COVERED in yellow toner. The slot for the toner cartridge is still clean. It won't calibrate: it throws "Calibration error consecutive DmaxDhalf" and "Calibration error Color Plane Registration" errors. The cleaning option didn't help.

My question please: is this old thing toast or worth trying to fix it?  I know nothing about printers, don't want to put good money after bad. Thanks in advance...

[Repairatrooper]

The yellow toner is defective. If a print defect is a single color, then a cartridge is normally the issue. With that much toner spilled it is possible that the registration sensors are blocked with toner, preventing calibration. Best to find a download for the service manual to see exactly where those sensors are.