I've got an old LaserJet 4V printer, which gives me an error 51 after printing the first page. When splitting a print job into single pages it will print it just fine, but that's no solution. The service manual says it is a "laser beam detection error" and suggests to check the cables at the scanner unit. I've already done that (tweaked the connectors of the sensor wire) and also cleaned the optics in the scanner. The connection from the photo transistor to the DC-unit is now at 2 Ohms, which I consider good. I haven't measured the other cables at the scanner unit but tweaked the connectors, too.
Is there anyone having experience with this fault? Is the problem maybe at another place, power supply, bad capacitor at DC-unit or something else?
Xpost c.p.p, s.e.r Fup2 s.e.r