I recently picked up a used, broken ProForm 505 CST Treadmill from someone at a really good price and decided to experiment with a repair myself, because the symptoms didn’t sound like it’s irreparable.
And I was right – the only thing I needed to replace was an IRFP250 MOSFET.
Symptom: The control panel turns on fine, but the motor will run for a fraction of a second and then immediately stop.
The repair is very easy: de-solder the bad MOSFET and replace it with a new one.
The bad MOSFET was shot, you can diagnose with a multimeter:
- Put the multimeter in continuity or diode testing mode, you should see a voltage drop between the pins on a good MOSFET and the pins shouldn’t have continuity between each other.
- On the bad one, the multimeter beeps in continuity mode on all three pins, meaning the MOSFET is completely shot.
