WM F-7 ABBA Diesel Set (20-20056-1)

bob gOGR Forum Member

I have had the Western Maryland set listed above since 10-2011. The cab numbers are (A Units 65 & 63, B Units 402 & 404). Recently the motor/wheels on the #63 unit (which takes up the rear in the consist) will start to turn, in the forward direction, as soon as power is applied to the track. The lead unit (#65) will go through its normal start-up sequence in neutral while the rear unit is spinning its wheels......I have tried eliminating the B units to try just the A units back to back......no success. Tried deleting the engine and reloading....resulting in the same symptom. Tried all the feature & factory resets....no success. Hopefully, someone on the Forum has some words of wisdom.....Thanks in advance for the help

10/1/1512:23 PM

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triplexOGR Forum Member DIGITAL SUBSCRIBER

You may have a damaged slave board in the trailing A unit. It is unable to respond to the info being sent to it from the lead A unit. I assume this is a Proto 2 ABA set.

10/1/151:05 PM

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gunrunnerjohnOGR Forum Member SUPPORTING MEMBERDIGITAL SUBSCRIBER

See if the trailing A unit takes off if it's all alone on the track without being connected to the master unit. If so, I'd agree with the previous comment that the slave board is damaged, probably the drivers.

10/1/151:11 PM

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GGGOGR Forum Member

Definitely a slave board issue and most likely motor fet short. It is repairable. G

10/1/152:27 PM

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bob gOGR Forum Member

The trailing A unit DOES take off as soon as power is applied to the track.

Two suggested solutions so far indicate the slave board is probably the issue. Not sure what a motor fet short condition would look or act like. As I mentioned, the trailing unit seems to run fine when on the track all by itself.....no neutral.......it just starts moving when power is applied.

Can this part be purchased directly from MTH? And can it be installed without "special skills or equipment"? If it can, are there any programming or other aspects of the installation that should be considered?

10/2/156:58 AM

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GGGOGR Forum Member

Yes you can buy the FET from MTH, it takes soldering skills to remove it and also replace it. No programming.

Occasionally it may also have another chip damaged, also repairable.

You can just remove and send the slave board, or you can replace the slave board if you can't solder. Slave boards are about $70. But you need a MTH ASC to get the board. G

10/2/158:15 AM

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gunrunnerjohnOGR Forum Member SUPPORTING MEMBERDIGITAL SUBSCRIBER

A motor FET short would look just like what you have.