Printer and Photocopier Troubleshooting and Repair Collection : HP LaserJet error code 51               
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HP LaserJet error code 51

"On self-test, pulls in paper, pauses, indicates "51 err." Then pulls paper through mechanism while "02 warming up" is displayed. Nothing prints, except for 2 horizontal black bars about an inch apart with grey in between them, about 1/3 from top of page. Since we stole this fair and square, and since we have a number of good (but _not_ laser printer) techs around, I'm wondering where we might dig. The book simply says error 51 means we should call HP service."

(Note: In the discussion below, the specific cable and parts IDs may not match your model.)

(From: Tony Duell (ard@p850ug1.demon.co.uk).)

It's called a 'beam detect error'. Let me explain what that means:

The laser beam is reflected off a spinning hexagonal (I think) mirror, and scanned across the drum. At one end of the scan the laser is turned on, and the reflected beam hits a fixed mirror (not the drum) and is reflected down an optical fiber to a photodiode on the DC controller board. The electronics on that board detects the pulse from that photodiode and provides a sync signal for the data sent to the laser

So the fault can be the laser, the scanner motor, assorted optical bits, the photodiode, or bits on the DC controller board. I think we can eliminate the motor for the moment, as that tends to give Error 52s.

Look at the PrinterWorks Web site (http://www.printerworks.com/) for exploded diagrams. Also read the section: SAFETY since you will be inside the printer near high voltage and possible exposure to laser light.

The official fix is to replace the scanner, the cables (electrical and fiber optic) between the scanner and the DC controller, and then the DC controller until the fault goes away. But you can often fix things

Start by pulling the casing. Over the paper tray there's a flat black box. Start be reseating the 2 cables (one under the flap) that go to this unit.

If you have an IR detector (as used for testing remote controls) then undo the screw on the scanner - not the fixing screws that hold the scanner in place - remove the grey optical fiber, and hold the sensor over the channel that the fiber fitted in to. Do not look up this channel - it can output laser light. Turn on, and try to print a test page - which will fail.

If you get IR light out of the scanner unit:

Reconnect the fiber at that end, remove the base of the printer, and arrange some way to prop it upright with the interlock switch pressed in. Unplug the fiber from J201 (a DNP-like connector) on the DC controller board. Put your IR sensor on the end of that and test again. No IR light now, time to replace the fiber.

Reconnect the fiber to J201 and hook a logic probe or 'scope to TP208 on the DC controller. This is the output of the photodiode amplifier. Do you get pulses here? If not, check the photodiode and the transistors Q202, Q204, Q208. If you do, then, alas the problem is most likely in a custom chip, and it's time to replace the DC controller.

If you get no light from the scanner, then it's time to inspect it:

Carefully trim back the moulded clips that hold the cover on the scanner and open it up. Clean the optics with a soft brush or lens tissue. The mirrors are front-silvered of course. There's a little shutter in the laser beam, opened when a toner cartridge is locked in place - is this opening correctly when you close the printer? If not, find out why not.

Unplug the cable from the laser PCB, power up the printer and try a test page. Does the scanner motor rotate? If not, we'll debug that.

The last possibility is that the laser isn't coming on for some reason. Debugging that is going to be interesting (read Sam's laser diode notes next :-), and I'll do the same) and I'll try to talk you through that when I know it's necessary. (Note: Sam's laser diode notes -- Diode Laser chapter of Sam's Laser FAQ.)

(From: Tom Dunn (dunnt@cco.caltech.edu).)

Error code 51 indicates loss of laser beam for over 2 seconds. Check -5 V, also make sure there is no interlock mechanism damage, and +5 V at J451-1 on Laser Drive PCA. You may need new laser unit. Good hunting.

(From: John Holcepl (john_holcepl@nls.net).)

This is a very common error on a HP Series II. An error code 51 is loss of beam detect. The cause is a bad cable between the DC Controller and the laser/scanner assy. P/N RG1-0908-000CN. Sometimes just reseating the cable will make this error go away but it will come back eventually.

(From: Eric Liber (liberes@westinghouse.com).)

Here is the description of the possible 51 errors:

51 ERROR (Loss of Beam Detect)

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