Reply to "Reverse board won't go forward, bad transistor or some thing else?"

stan2004OGR Forum Member

Another bad board?

I've never seen one of these but I'd guess a better than even odds one of the power transistors popped. This is undoubtedly a so-called "bridge" drive which has 4-transistors, 2-NPN and 2-PNP or 2 each of the MJF44H11 and MJF45H11. In one direction, one N and one P are "on". In the other direction the other pair are "on". If one or both in a pair fail, the motor will not spin for that direction. These are carried by Mouser and DigiKey for less than $2 each though DigiKey is out of one of them.

Do you have a voltmeter? If so and you have a steady hand (to poke around with power on) I think I can help you isolate which transistor is bad. Or one of the Lionel repair techs might step up with a direct plan of action.

1/3/121:47 AM

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