HP LaserJet 42X0/43X0 -- Tray 2 Won't Lift; Motors Don't Turn

The 4250/4350 machines have a sensor in the paper path that the 4200/4300 printers don't have. That sensor, if actuated at power on, produces a very odd symptom; there's no motor operation and Tray 2 doesn't lift, yet the machine ends up displaying 'READY'. The machine is completely inoperative in spite of the apparent 'READY' condition.

The sensor that can cause that to happen is PS109, Paper-Width Sensor #2. It's only present in the 4250/4350. Here's a view of where it resides.

(In the photograph, the registration assembly's flap is pulled back and held away.)

The sensor at the left is PS106, Paper-Width Sensor #1. The central sensor is PS103, the Top-of-Page Sensor. Way over to the right is PS109, Paper-Width Sensor #2. That's the one that can bring on the symptom.

We ran into the problem here right after one of the guys replaced a registration assembly in a 4250 -- no motor operation, no Tray 2 lift, yet the display said 'READY'.

It turned out that he'd installed a 4200/4300 registration assembly in a 4250. The 4200/4300 registration assembly's flap doesn't provide clearance for the additional sensor, so the sensor is always actuated. Here's a view of the two different registration assemblies.

Above is the 4250/4350 registration assembly P/N RM1-1098. Below is the 4200/4300 registration assembly P/N RM1-0011. Note the absence of a clearance punch-out for PS109 on the lower assembly's flap. That's what brought on the symptom.

It appears that HP has discontinued P/N RM1-0011, and is only supplying P/N RM-1098, the 4250/4350 style. That registration assembly will work in 4200/4300 machines as well as 4250/4350 machines. However, refurbishers are still supplying P/N RM1-0011, so those are still around to make the mistake with, which is exactly what happened here.

Needless to say, a shard of paper trapped under the registration assembly's flap at PS109 would bring on the same symptom. It must be a bug in the printers' firmware that's at the root of this; the printers ought to report a paper jam condition when a sensor is actuated at power on -- not come supposedly 'READY'.

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