Tuesday, July 17, 2012

Broken Logitech G25 Part I

Wanted to play a little GT5 over the previous weekend. Hooked everything up and turned the PS3 on.

The G25 normally does a little calibration routine at the start, but this time it did a little quarter turn and sat there motionless. Power LED on the shifter just kept blinking, I thought WTH and decided to try rebooting the PS3. Nope, this time it wouldn’t even move and just kept blinking.

Plugged it into my PC, and everything works, except the wheel. I’m guessing without the calibration routing, the wheel axis will not work.

Measured the power coming out of the adapter and it was a stable 24V, as per the spec on it’s label.

Next I tore into the wheel itself to do a little poking around.

The 1st thing I suspected was the motor driving circuitry. Disconnecting both motors and probing around the vicinity confirmed that I was right, one of the dual MOSFETs in the IRF7103 was a dead short.

Proceeded to remove the FET and see if it’s really dead, or something else on the board had died.

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Yes it was dead. Removed and re-probing with my trusty DMM confirmed that. I put both the FETs on order (IRF7342 and IRF7103) thru RS-Components (actually only the IRF7103 had fried, and it was a single FET in the dual FET package).

I then decided to find out what exactly killed the FETs, wouldn’t want my replacement to go up in smoke the second I powered it on, why did the wheel turn 1/4 way before coming to a stop?

Removed a couple of screws and disconnected a bunch of stuff to get the gearbox and motors out where they could be comfortably moved around. I then decided to probe the resistance of both motors.

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Here you can see that one motor has an encoder (where I guess the wheel actually gets it’s axis signal).

A pic of the reading I got from the motor with the encoder on the back. This is the min resistance (I spun the motor slowly by hand and used the DMM’s min function).

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One of the ‘other side’

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I pulled the motor leads out of it’s connector and tried using the power adapter itself to power the motor with the encoder. Bad idea, a whole bunch of smoke came out of the commutator area and the motor just jerked a little and sat there pretty, whilst more smoke poured out. I quickly disconnected the wires.

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Can’t really see the commutator in this pic, I then disassembled the whole motor so I could see what was going on inside, initially I suspected that maybe a winding was somehow shorted or the brushes were somehow shorting together.

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Here’s what I saw after prying the back out. Look at the gaps in between the comm segments. A mixture of oil,grease and carbon has built up inside and I’m guessing is the cause of all the problems I’m having.

I dug through my drawer and found a little pin that was small enough to fit into the gaps and used that to clean it out. Together with some contact cleaner.

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This is the amount of crap that flowed out.

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All that black stuff came from the commutator. After cleaning I measured the resistance again.

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Not too bad I’d say, pretty close to the other motor. For that motor I just sprayed a little cleaner into the comm through the side gap and called it good.

Piecing the thing back together. I had gouged the end ‘tabs’ a little during the disassembly, and ended up just using a small punch to wack 4 tabs back on afterwards, seems to be tight enough to me.

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I also noticed a little crack on the encoder wheel and used a little bit of CA glue to stick her back together. The wheel just slides onto the shaft and is held there with friction.

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Look forward to Part II where I replace the fried MOSFET and try powering her up! I have the parts on order right now and am waiting for them to arrive.

9 comments:

  1. Waow!
    Big thanks for your tuto.
    I had the same problem...

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  2. Have the same one!
    Try to repair.
    Thanks

    ReplyDelete
  3. replacement encoder made of solid brass...

    www.cmlaserservice.com

    ReplyDelete
  4. Could you suggest me what to do?
    My problem is:
    Starts to calibrate - Turns all the way to right, then all the way to left and stops calibration. Then thinks few secs and tries to calibrate again and stops again, does like this 3 times and finally does noting.. Power led just blinking..
    At first it just turned right and stopped at the middle, but now its going all the way to the left too..
    This came after I did my first drifting attmept, wheel got pressured about 1-1,5hrs ( a lot of fighting with ffb - like turning against ffb to control the car.. ) then just noticed its not centered and after unplug - plug this stuff started to happen.
    Any ideas please? :(

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    Replies
    1. Have you taken it apart to see what's wrong with it? I'd suggest measuring the motor to find out if it's still good, as well as a visual check on the encoder wheel on the end of one motor.

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    2. Same problem with me too, I bought a new encoder wheel but that didn't fix the prblem..Did you fix yours ? and can you tell me what was wrong

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    3. I haven't got the same issue like this, is the pickup for the encoder wheel clean and reading the motion?

      Next thing I can think about is are any of the gears not transmitting power properly? The control board may give up if it doesn't get the motion it expects.

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    4. How do I check the gears are working correctly ? and the enocder pickup?., Mine is the exact same problem as @MLepassar has. I have ran it without the encoder part on and it gives the classic calibration issue and connected up the same as @MLepassar. I'm running out of ideas on what the issue you may be, I don't see anything blown on a visual check

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    5. Gears are easy, just make sure they are engaged to one another and not cracked, you can probably check this through the side with the wheel disassembled like I have and slowly turning the wheel around to make sure it's good. I can't remember how the motor shaft is connected to the gears, but I'd also make sure it's tight. Else the feedback from the encoder will not make sense to the controller.

      As for checking the encoder, you'd have to make sure there is power going into the encoder, and then a train of pulses coming out the output, will probably be possible to do with a fast multimeter, with a normal multimeter you should see a fluctuating voltage out the output as the wheel is turned, will probably have to map out the pinout on the encoder.

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