B737-NG windshield wiper uncommanded motion
Thread Starter
Joined: Jul 2010
Posts: 431
Likes: 1
From: OFCR
B737-NG windshield wiper uncommanded motion
A few days ago, in climb phase, I noticed the right wiper began to move without me or my cpt touching the related switch. Just a couple of sweeps and then it stopped again.
Has it happened to anybody else? What could be the reason?
PG
Has it happened to anybody else? What could be the reason?
PG
Joined: Feb 2004
Posts: 1,410
Likes: 37
From: Australia
There's not much in the system:
CB, control panel and combined gearbox/motor/control circuit (behind the wiper)
The CB provides power to the wiper motor, but a second variable voltage supplied by the control panel to the the wiper motor assembly controls PARK/INT/LOW/HIGH.
For some reason, a stray control voltage is getting to the motor assembly. There are a few diodes in the control panel, maybe they were breaking down and affecting the output voltages from the control panel. Or maybe the contacts of the switch were faulty. The panel is the easiest to change. Given that the fault was very intermittent and unlikely to be faulted on the ground, the engineers would have probably changed that as a first course of action.
CB, control panel and combined gearbox/motor/control circuit (behind the wiper)
The CB provides power to the wiper motor, but a second variable voltage supplied by the control panel to the the wiper motor assembly controls PARK/INT/LOW/HIGH.
For some reason, a stray control voltage is getting to the motor assembly. There are a few diodes in the control panel, maybe they were breaking down and affecting the output voltages from the control panel. Or maybe the contacts of the switch were faulty. The panel is the easiest to change. Given that the fault was very intermittent and unlikely to be faulted on the ground, the engineers would have probably changed that as a first course of action.
Joined: May 2012
Posts: 131
Likes: 0
From: Australia
If the same as a car wiper, there is a home position switch. In this position the power must be applied by the windscreen wiper operation switch/circuitry to move the motor away from the home position. Once it is away, a constant supply voltage runs the motor to allow it to sweep return to the home position.
Thus when the wiper is away from home position, turning it off will not stop it operating until it returns to engage the home position switch.
If the home position switch is faulty, the wiper could be able to run by itself continuously.
Thus when the wiper is away from home position, turning it off will not stop it operating until it returns to engage the home position switch.
If the home position switch is faulty, the wiper could be able to run by itself continuously.
