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The picture shows the inside of my TCU wastegate servo where the tip of one wiper has broken off and is now stuck against (perhaps with dielectric grease) what appears to be a screen printed resistor that is used by the TCU to measure servo position. 

The symptom was a jammed wastegate cable and a blinking orange TCU light that appears about 6 seconds after power up (not immediately like what happens with a disconnected sensor).  After I removed the jammed cable from the servo wheel, the servo rotates "too far" on power-up -- clockwise past the cable mount before returning to the start position.  No wonder the servo and cable were jammed.  When I opened the servo, the broken copper wiper was obvious.

Has anyone else seen this?  Can I buy a gear with the copper wipers, or maybe just the wipers themselves?  This happened suddenly: 2 weekends ago everything was perfect, last weekend -- blinking light.  This weekend -- disassemble until problem found.  I can't imagine that I'm the only one with what amounts to a potentiometer with a bad wiper.  This is certainly not a $500 failure (cost of new servo).  Thanks.

8538_1_IMG_2588.JPG (You do not have access to download this file.)
  • Re: Servo potentiometer wiper tip broken - is there a cheap fix?

    by » 4 years ago


    Here are my thoughts:

    1. If it performs a flight critical function then whatever you do make sure that it is going to be reliable.

    2. I think that the chance of finding an identical wiper finger assembly is slim. Does the manufacturer of the servo make anything else similar?

    3. You could purchase a rotary encoder switch, disassemble it, cut off one of the fingers, trim the original broken one and solder the 2 parts together. This would make a new finger of the correct length with a new contact.

    The only other places that I've seen this type of wiper finger is on things like windscreen wiper motors, linear actuators and car engine MAF sensors that use a flap, like the old Bosch ones.

    That's the best that I can come up with.


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