It's been a couple of months since I've posted anything but I have been kept busy with installs. They've mostly been routine ones that I had already covered on this blog. But recently I was asked to replace the decoder in a Bachmann Spectrum 44 ton switcher with a TCS Z2 or similar small decoder.
I was not very familiar with this model so I checked it out on the web. It seems that Bachmann offered this model only in a DCC version and that no DCC manufacturer offers a replacement decoder. Also on some of the forums there was mention of problems with programming this decoder.
This model uses the tested method of bumps on the frame / dimples on the inside of the shell to hold the shell in place. It's a tight fit and after trying a few methods to get the shell off, this was the one I found the easiest.
The trucks will come off fairly easy so I took them off first then placed a jewelers screwdriver between the fuel tank and the shell and gently pried.
Once the shell is off, we can see the original decoder board. The decoder is secured to the frame with 2 small screws, one on each frame half.
The decoder has mostly surface mount components with a couple of coils on the bottom and what the instruction sheet called a thermal fuse link in series with the motor.
The way this component was installed in the motor wiring instead of on the board suggest to me that it may have been an after thought.
I made two custom LED boards from a two stock Kato LED boards that I had in my collection. This photo shows the modifications I made to get what I wanted.
Here are the 2 new LED boards that I made from a Kato LED boards. Don't know what engine it originally came from. I wanted something with surface mounted LED's. The new boards are secured to the frame by the original screws and provide track connection to the decoder. I spliced the decoder wires onto the motor wires so I would not have to remove the motor.
Here's the side view of the finished mechanism. One of the nice things about the LED boards I made was that they are single sided meaning that I don't have to worry about anything on the bottom shorting on the frame. The space where the coils of the old decoder were could be used to add a bit of weight.
The inside of the shell of this loco offers an opportunity to add quite a bit of weight to this loco in the cab where the black plastic box that was attached to the original decoder had been. I painted the inside of the cab windows a dark gray, then attached 2 layers of lead strip to the roof. Another area where weight can be added is along the inside of the cab side walls below the side windows.
If the replacement LED boards, decoder, and wires are not interfering with the shells fit, the shell should rest on the parts of the frame that stick out as shown in this photo.
Here is the completed engine. With the weight that was added it is close to the same weight as a stock Life Like SW type switcher and has about the same pulling power.
