PRR NW2 - Motor Replacement
10/22/2010
I started noticing problems with my engine. On our Houston S Gaugers club layout the engine would short out from time to time. At home it ran fine for about a year and a half. Then I started noticing that it would stop, blink the headlights nine times, and then move on again as if nothing had happened. At first it was random, every once in a blue moon. Then it started happening more often. Finally, one day one of our club members came over to see my layout and the engine went through this process about five times during its 20-foot run on the layout (gremlins always come out during demonstrations only). At the next club set-up I had replaced the Tsunami decoder with a Digitrax DZ124 decoder to determine whether it was the decoder. It ran great at home. At the show, the engine ran for about 15 minutes, became very hot, and then shorted out. Smoke came out of the shell, and sure enough, the Digitrax decoder was fried. Several of the club members discussed my problem and the general consensus seemed to be that there might be something wrong with the windings of the original motor in the engine. This would explain the symptoms. The motor would get a little hot and the engine would short out. Maybe as one of the windings got hot and expanded, it caused a short.

I placed an order with S-Helper Service for a new motor. It arrived the day before one of our big shows. I replaced the motor before the show and the engine ran great for about 5 hours the first day and about 6 hours the second day of the show. Once it was back on my home layout, I ran it through some of its switching duties and the engine ran perfectly the entire time. The Tsunami decoder works fine too. So, the conclusion was that the original motor was bad, and the Soundtraxx Tsunami decoder is very resilient to be able to handle the motor shorting out. This page describes how I replaced the motor.

To replace the motor, follow the Disassembly article I wrote for gaining access to the motor. Once the boards are removed and the decoder unplugged from those boards, the photo below shows what you're left with. The loose motor is the new replacement motor. The original motor has "8A 24V" stamped on its sleeve. This is quite a large motor. The motors have the same physical dimensions; it just appears different due to the angle at which I took the photo.
Motor Replacement
There are two wires soldered to the motor's terminals that need be unsoldered. A rubber-like sleeve covers the terminals. These can be moved back using a pair of needlenose pliers or a firm pair of tweezers.
Motor Replacement
Once the wires are loose, you will see two plastic "clamps" over the motor holding the motor firmly in position. Each of those clamps has two screws that attach to the frame. Once you remove those, the motor can be removed. The U-joints may put up a little bit of a fight, but the motor should snap out.
Motor Replacement
The new motor goes in easily. Adjust the U-joints so that they line up correctly. They snap into place much easier than they were to remove. The motor now sits loosely in the engine's frame. The two clamps need to be installed to firmly hold the motor in place. This was actually the most difficult part of the process. What made it difficult was that I wasn't getting them into the right spot. There is a plastic cradle in the frame into which the clamps need to fit. If you don't get them in the right spot, the motor won't turn over. That is a simple check to see if you did it right. The motor will be pushed down quite a bit to get it to all fit well. The cradle is identified in this close-up photo.
Motor Replacement
Once the clamps are re-attached, you can solder the motor terminals to the orange and gray wires, install the circuit boards with the decoder, plug in the shell's wires, and re-attach the shell. I had a couple of issues after the motor replacement that I want to capture here. First, the red electrical tape that was used in the factory installation cannot be reliably re-used. I also had a hard time keeping the circuit board, to which the decoder plugs in, staying attached to the smaller circuit board. I finally wrapped the two tightly together with new black electrical tape. I would recommend test running the engine without attaching the shell (leave its plug disconnected) to make sure everything works before attaching the shell again. The double-sided foam tape that held the decoder in position also couldn't be re-used. I used a new section of Velcro to attach the decoder to the motor. The last problem I had was that the engine became very herky-jerky at slow speeds. I tried playing with the decoder's settings, but nothing helped. I opened up the engine again and found that the small capacitor that is soldered across the leads of the motor had come loose. I had already noted that the new motor was quite a bit noisier than the old one. I soldered the capacitor back in place, and both the herky-jerky motion and the noise disappeared. That small capacitor is very important. My engine now runs perfectly again, just like it did when I first got it. I hope this motor will last. Don at S-Helper Service told me that very few of these motors go bad, so I may have just gotten a lemon in the original one.
Motor Replacement