Wednesday, 18 May 2016

Fellowes 99ci repair part 1

I picked up a reconditioned Fellowes 99ci shredder a while ago as it was significantly cheaper than a brand new model. For a while it worked well enough but as shredding isn't something I do particularly often by the time it started to have issues it was of course out of warranty.


It has been quite a while since it died and I can't remember the exact details of what happened but I think the motor wouldn't turn despite the bin being empty. Googling around for issues with this particular model always came back to advice such as:

"You should be able to flip up the cd cover and visibly see the sensors in the center of the paper entry(look like little LED lightbulbs) Clean with a Q-tip dipped in rubbing alchohol. This should solve your problem. If it doesn't you probally have a burned out sensor".


Taking the shredder apart revealed a single main board and several smaller boards which provide status indicator functionality and button support.

Going on the advice from Google, I initially checked the various sensors and switches in the hope of finding a dead one but they all turned out to be fine. A visual inspection of the main board didn't find any obvious damage so it was necessary to do some live testing. Not having an isolation transformer means I'm not really a fan of working with mains electricity so I'd been putting off probing about the main board longer than I really should have. Eventually I figured out the bits that would hurt if I accidentally touched them so making sure I stayed well clear I was able to check if the power was getting to the correct bits

The top side of the single sided board. 


An inverted view of the bottom side so that the traces 
line up with the component placement above.

A combined view which makes it clearer how
the various components connect.

The brains of the operation is a PIC16F883 but it was clear the digital side of the board was unlikely to be the problem. The voltage coming out of the 7805 regulator was fine and even manually triggering the relay didn't start the motor. The issue had to be on the power side and in the end it turned out to be a dodgy triac. The component in question is a BT137-800E 800V 8A triac and is the component attached to the heatshield in the upper right section of the board.

A couple of replacement parts from ebay later and the shredder fired into life! Except the motor wouldn't stop and eventually it ground to a halt with a distinct burning smell :( So it looks like the motor is the next problem to solve. It might be as straight forward as replacing the bearings or it could need a rewind, so the future of this reconditioned unit isn't exactly looking bright right now.




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