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Dilbert Electronic Candy Dispenser Troubleshooting & Repair

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Dilbert Candy Dispenser - RF CafePrying Off the Computer Front Cover on Dilbert Candy Dispenser - RF CafeMy daughter, Sally, recently bought me a Dilbert Electronic Candy Dispenser at a second-hand store. We soon learned the reason it was there and not dispensing candy electronically on someone's desk.

When I loaded in a fresh set of batteries and pressed Dilbert's computer mouse, nothing happened. I whipped out the DMM and measured the voltage at the two AA batteries as 3.2 V with the switch open, and about 2 V with the switch closed. The system was getting voltage and drawing current, but nothing was happening.

Dilbert Candy Dispenser Slots in Computer for Front Cover - RF CafeDilbert Candy Dispenser Computer Front Cover - RF CafeI disassembled the contraption (no easy task), and assessed the situation. The cam-operated shutoff switch was crammed against a stop, but it was not apparent why. I then pried out the little DC motor and verified that voltage was getting to the motor. Having messed around with many similar motors as a kid, and noting that basically nothing has changed over the years, I confidently unbent the two case retaining tabs and pulled the rotor assembly out from the stator magnets.

RF Cafe - Dilbert Electronic Candy Dispenser -- start switch and stop switch cam shownThe key to getting it apart is removing the CPU front cover beneath the computer monitor. I used a thin metal 6" engineering ruler (scale). The cover snaps in on each side with a little locking tab. It will take a lot of force to pry the tabs out of the holes, but I have done it at least three times with no damage to the tabs or the mating holes.

Be sure to note the placement of all the gears and cams as you disassemble everything since the timing of the electrical switch is dependent on getting it back together correctly.

RF Cafe - Click here for a page with a small DC motor animation showing how the brushes and commutators work. See the 3rd image down; it is a 3-pole motor like the one in the Dilbert Electronic Candy DispenserThere were carbon deposits all over the brushes (2) and commutators (3), along with some poorly applied grease that was supposed to be at the rear rotor support (not on the brushes). A little MEK on a Q-tip took care of the misplaced grease, and then some 600 grit sandpaper on the brushes and commutators took care of the carbon deposits. The motor was reassembled and then fired up while still outside the dispenser housing.

RF Cafe - Dilbert Electronic Candy Dispenser -- stop switch cam shown in the centerAfter reinstalling the motor and aligning its gear with the main dispenser gear, I pressed the start button and it immediately started to run and then stall. I hurriedly removed one of the AA cells to prevent damage; it is not possible to put the batteries in backwards. Upon close examination of the situation, it became obvious that the entire gearworks was running backwards, causing the cam-operated shutoff switch to get jammed into the cam rather than ride over the top of it. A quick reversal of the two wires at the battery box rectified (literally) the problem; soldering required.

RF Cafe - Dilbert Electronic Candy Dispenser -- blue & black wires had to be swappedEverything else was cleaned (remember that it was second-hand) and reassembled. The video below shows the results.

Posted November 16, 2009

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