Bosch Dryer WTA3500 UC

[AnotherHeadache]

My Bosch dryer does not start. Everything looks normal, except the drum doesn't rotate. I tried the auto dry and timed dry cycles and it appears the cycle starts (drying light comes on and if on timed cycle timer counts down). Problem has been posted some time ago with no solution. Tested door switch. Has anyone come across a solution?

[ScottyMo1]

These units have a belt switch that can be tripped if for any reason the drum is rotated the wrong way. If you remove the rear panel, you can access it. Push the button and you will feel it engage. May take care of the problem. Let us know what you find.

[AnotherHeadache]

I removed the back panel but there is no rear panel. The only components under the cover are the motor fan and the heater. There is an over heat trip sensor with a red reset button (it wasn't tripped). I am attaching a picture of the back. I removed the side panel to access the motor. I checked the motor starting capacitor with a tester and it tests ok. I tested and do not appear to be getting power to the motor plug (I modified some spade lugs to fit the plug for testing). I am assuming I would still get AC power from the control board to the plug even with it open (unplugged). Based on this I am assuming it is the relay or some other part of the control board circuit. Any other suggestions?

[ScottyMo1]

If there is no voltage to the motor plug. I would suspect maybe the board or see if there is a cut off device somewhere in line between the motor and the board.

[AnotherHeadache]

I checked the schematic and the only thing between the AC supply (through a relay) and motor appears to be the overheat sensor. The door switch feeds into the board, but I checked the door switch. Do you know what are the 2 spring loaded, carbon brush type sliding contacts on the front and toward the back of the drum for? I took a chance and ordered a new control board, hopefully that is the problem. Will keep you updated. Thank you.

[AnotherHeadache]

  , not the control board. What would the drum "conductance" be for? I removed the plug from the control board and measured from the drum to the wire on the brush and the front brush measures about 25 ohms and the back brush is measuring open. I tried just shorting the brush wire to the drum and motor still doesn't start?

[JWWebster]

Might be the capacitor. This fellow from Espares has a lot of great videos on getting into these machines and repairs:

[washman]

Hi


One of the drum lifters has sensers in it, the 2 arms on to the drum make contact for the dryness control.


Mike  (washman)

[AnotherHeadache]

Would loss of contact with the drum stop the motor from starting? The sliding contact is definitely not contacting the drum( checked with a multi meter). The motor doesn't start in timed dry or air fluff mode either.  Thank you.