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Old 03-20-19, 06:10 PM
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steelbikeguy
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Originally Posted by kevin999
Okay, at long last. Here is the picture of the circuit board. The part in question is bottom middle, labelled Q1, with the red box drawn around it.

well, I can see why you thought Q1 might be bad!
what the heck happened to it, though? There's no sign of overheating, which is usually why chunks of the package get blown off.

Based on what I can see of the circuit board traces, my first thought was that Q1 was used to prevent reverse application of power from the connector on the right. However, the source and drain should be connected opposite of what they are, so that idea is out.

The next (last?) idea is that it might be a N channel mosfet (or npn transistor) switching a high side load. I think the diode, D1, is meant to be a freewheeling diode to handle inductive kickback. That load would be whatever hooks up to the two-pin connector on the left......



so what connects to that??
Whatever it is, that should be the only part that isn't working.

and just out of curiosity.... what does this gadget do? There's almost nothing on it other than the bluetooth radio mondule.
edit: the internet tells me that this is for an indoor trainer, so I'm guessing that the "brake" is somehow controlling an eddy current brake that acts as the drag for the trainer. It's probably an inductive load, and probably pwm'ed, so the flyback (or freewheeling) diode is important. It might be important for the mosfet to have a low Rds to avoid overheating, in the event that it is carrying much current.

anyway... my guess is that this is a N channel mosfet from On Semi (formerly part of Motorola). The code on the package is mostly just telling when and where it was made. The actual device info is probably on the part of the package that's missing.
Here's a datasheet for a somewhat similar mosfet from On Semi..
https://www.onsemi.com/pub/Collateral/NTD3055-150-D.PDF
The package is a D-PAK, and any logic level N channel mosfet is probably okay.

Anyway.. that's my guess. Looking forward to finding out what I overlooked.

Steve in Peoria

Last edited by steelbikeguy; 03-20-19 at 06:23 PM.
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