Deciphering '01 Audi A3s power windows module - Page 1
Forum section: electronics / repair

author: bborisov567
author_rank: Regular Contributor
timestamp: June 27, 2021, 08:54:32 pm
content: The operation of the module should be fairly straight forward. I am not optimistic about finding any kind of schematic but i can post the part number if somebody is feeling confident. It reads the input from the buttons and rolls the window up or down. When the window has reached the end position the modules senses higher current (probably?) and shuts off the motor relay. The problem with my modules is that it rolls the windows down but the current protection strikes when i try to roll it up (i hear the relay clicking). The motor and the mechanical part are ok. I measured the current and it is the same in both directions. Opening the module reveals an ic (i couldn't seem the find datasheet), couple of BJTs and a pair of hall sensors (marking is "525k" ). Each of them is near to the ends where the pins of the motor connect. I measured the power supply with the module attached to the car - both sensors get 5v. Then i desoldered them. After testing the first outputs 0.21v, the other 0,18v. Also they act like a toggle switch - once there is a magnetic field output is high and stays like that until i remove the magnet i get it near the sensor again. What i can't seem to understand is how the amount of current is measured so that the circuit knows to stop the motor at the end position.

author: shakalnokturn
author_rank: Super Contributor
timestamp: June 27, 2021, 09:37:50 pm
content: I don't see any resistive current sensing on the PCB itself.The hall sensors could be used for current sensing if close enough to the motor supply conductors or they're close enough to a rotating part to detect a jammed motor and cut the relay after a short period.

author: bborisov567
author_rank: Regular Contributor
timestamp: June 27, 2021, 09:59:45 pm
content: They are close to the motor supply conductors, not the rotating parts.

author: YetAnotherTechie
author_rank: Regular Contributor
timestamp: June 27, 2021, 11:10:32 pm
content: Have you done the reset procedure, how do you know the motor/gearbox is good?

author: bborisov567
author_rank: Regular Contributor
timestamp: June 27, 2021, 11:35:01 pm
content: What is that reset procedure? I know the motor and the gearbox are fine because when i supply 12dc i run fine and consumes the same amount of power in both directions. Also i tried putting the module from the working side on the motor and everything works as expected.

author: amyk
author_rank: Super Contributor
timestamp: June 27, 2021, 11:48:29 pm
content: That's almost certainly a custom microcontroller or similar. If it's faulty, a replacement is unlikely to be found for a reasonable price.Another case of increased complexity leading to decreased reliability... all older vehicles just use a bimetallic circuit breaker, if you hold the switch down against the stop you'll just hear a click periodically.Maybe converting it to that type of system would be a cheap solution if it's the electronics at fault.

author: YetAnotherTechie
author_rank: Regular Contributor
timestamp: June 27, 2021, 11:50:00 pm
content: https://youtu.be/-dEjjASrfBo

author: elektrolitr
author_rank: Contributor
timestamp: June 28, 2021, 08:59:39 am
content: These Hall sensors are most probably part of rev counter so the controller knows the position of windowCheck the location where the Hall sensors are for any moving parts with magnetic propertiesIt is normal to stop closing the window if the shaft doesn't rotate (or there isn't signal from Halls) because it means the window is stuckI've attached the picture of one motor I have on hand- there is a ring magnet on the shaft and the hall sensor beneathOn other system the motor is separated from electronic part, and the guide pin of connector is made from steel, acting as magnetic conductor.

author: bborisov567
author_rank: Regular Contributor
timestamp: June 28, 2021, 08:21:21 pm
content: The idea of metal pins conducting magnetic field and rpm sounds quite plausible. I will look at the motor assembly closer to confirm or deny. But why there are two hall sensors. One should be enough for rpm reading.

author: shakalnokturn
author_rank: Super Contributor
timestamp: June 29, 2021, 12:38:12 am
content: True.One should be enough for a current reading too.

author: bborisov567
author_rank: Regular Contributor
timestamp: June 29, 2021, 12:11:51 pm
content: The only benefit of two sensor design is the ability to measure the direction of current which i guess is still important but doesn't give an explanation how the current protection circuit functions.

author: bborisov567
author_rank: Regular Contributor
timestamp: June 30, 2021, 07:49:36 pm
content: UPDATE: I finally managed to find how everything is functioning. The hall sensor pair monitor the rpm of the motor shaft. The magnetic field is transferred through the steel pins used for delivering power to the motor. You can see them going close to a magnet ring on the shaft. There is no such thing as a current protection. The microcontroller just shuts the relay if there is no rpm signal for more than two seconds. This represents case of jammed window. What seems to be the problem in my case is a bad relay contact. And since no current can't get to the motor, there is no rpm signal coming back and the microcontroller shuts down the output because it thinks the window is jammed and tries to protect the motor.