Question about bad constant lighting circuit in MTH non-powered unit

PRRMiddleDivisionOGR Forum Member

I have two MTH U-25-B non-powered units from what I believe was the first run. The NYC unit developed a short not long after I purchased it, and was repaired by MTH. Now, by PRR unit has developed the same issue. It began with sparking where the front truck rotates in the hole in the frame. Eventually it developed a dead short, then it developed the smell of burning electronics. I opened it up, and it looks like there are two bad diodes on the front constant lighting circuit board. Disconnecting this board eliminated the short, so I'm almost certain this is the problem.

I looked at the MTH website for this unit (20-20146-3), but there does not appear to be a parts diagram for this unit, unless I'm looking in the wrong place.

Has anyone had this sort of experience? Did MTH have a run of bad constant lighting circuit boards? Anyone have a part number?

And yes, I will be contacting MTH regarding this, but just wanted to see if anyone had a similar experience and could identify a bad circuit board as a cause of the problem.

Thank you.

4/28/137:41 PM

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Dale HOGR Forum Member

Not familiar with the circuit. For a couple of bucks you can make your own and install. Less aggravation unless in is a warranty issue.

Shown here

www.jcstudiosinc.com/BlogShowT...=619&categoryId=

Dale H

4/28/1310:23 PM

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AGHRMattOGR Forum Member SUPPORTING MEMBERMEMORIAL SUPPORTER

Some MTH diesels had a problem with the insulator that shielded the wires running up from the pickup rollers. The frame would shave through the insulation on the wire and would short intermittently (or worse, provide a "resistive short") and burn the insulation. If you remove the trucks you can inspect it pretty easily.

4/28/1310:33 PM

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PRRMiddleDivisionOGR Forum Member

Thanks guys. I assumed it was the problem Matt described above, but I checked the wires coming from the pick up rollers, and there is no evidence that the insulation is shaved. I then disconnected the red wires held together with the wire nut. When the circuit board for the front headlight was disconnected, the problem stopped. The back headlight still worked fine. This is why I think it is the circuit board for the front headlight.

Any other experiences/thoughts?

4/28/1310:40 PM

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AGHRMattOGR Forum Member SUPPORTING MEMBERMEMORIAL SUPPORTER

Originally Posted by PRRMiddleDivision:

Any other experiences/thoughts?

You've got E-mail, Neal

4/28/1311:12 PM

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Hogmaster 1OGR Forum Member

I had the exact same problem with a Premier Reading GP-35 NP unit. I had it on my layout for about 10 minutes. It was just sitting on the track when it started smoking and that unmistakable odor of fried electronics fill the air. Since I always run NP units with their lights off, I simply removed the center rail pickups. I'm not going to both with the hassle of sending it back to MTH's vaunted service dept. for an extended vacation.

4/30/136:57 AM

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