One week after the warrantee expired the machine stopped working while grating cheese. Parts are me expensive than a new one but I'd like to educate myself and find out what broke.

The safety switch works. I get no voltage out of the control board red/ black wires. If I apply 14 volts DC to the motor it spins.

Here is a picture of the control board. Does it convert household AC to DC? I see a MOSFET there, so is this a variable frequency drive? Pulse width modulated?

 

I see four big diodes so the board is probably making DC. And, if the motor ran when you fed it DC and the board has motor + and - that's a further clue that the board converts AC to DC.

You said no power was coming out of the red and black wires. Is power getting to this board, probably the brown and white wires in the upper left?

What model number appliance are you working on? Are there other control boards in addition to the one you posted?

 

This is a KFP0718. This picture shows the rest of the circuits.



Power goes first to the red wire in the safety switch (12 O'Clock in the photo). Brown wire with switch on gives 120VAC.

The switch pad is at 5 O'Clock and doesn't appear to have electronics except for LED indicators.

The small board on the motor itself looks to be a speed sensor.

 

Did you check the safety sensor loop ?
It's hard enough to get the container in and aligned right.

Did you check F1 ? It looks to be 4amps.

 

Also look at C3.
It looks like the top may have swelled up.
A sure sign of a bad electrolytic capacitor.

 

I checked F1- no continuity. Who knew that a manufacturer would solder a non-replaceable fuse onto a board? Talk about planned obsolescence.

A jumper across and triggering the safety switch gets the LEDs to light and a relay clicks. I don't have enough hands to assemble and jump the wire at the same time for a full test.

I have a fuse holder and slow-blow ceramic 4A fuses on order. Once they are installed I'll report back.

 

Who knew that a manufacturer would solder a non-replaceable fuse onto a board?
It's done all the time. Unfortunately many items are considered disposable and not made for repair. I'd be happy is they stopped welding plastic housings together or relying on single use snap together construction. Give me screws so I can open it up. It would also be really nice if they put more labeling on circuit boards. If you've ever had a resistor charred so you can't read the color bands a simple value printed on the board would be a huge help. Don't get me started on some of the tricks Apple and Samsung are doing with their phones to make them unrepairable by 3rd parties.

 

It's called a catastrophe or CYA fuse. It protects the manufacturer from lawsuits.
If it blew..... your motor is drawing more current than intended.

 

Success! A simple fuse holder with 20 ga wire, soldered onto the board in place of the factor fuse, and a 4 amp slow blow ceramic fuse. The appliance operates perfectly.

 

Good job. Thanks for letting us know how you made out.

 

Good job sticking with it and figuring out the problem. Most people wouldn't even bother opening the housing up to look inside.