If you want your new MEC SW-9 to run on your DC layout and reverse direction with DC track polarity instead of the standard forward-neutral-reverse sequencing, then this article is for you! Converting to DC polarity reversing is easy, but I thought it would be useful to document the procedure for anyone who hasn't done it yet. Remember, this is only possible on a DC layout, don't use with AC! This article also covers the first steps to adding DCC, if that is your interest. There are several photos, so please be patient while the page loads. You can click on any photo to get a larger version.
The new MEC SW-9 (and the next runs of SW-9s, SW-8s and NW-2s) have speakers mounted in the body for sound. Consequently the socket on the chassis for the LocoMatic sound unit, DCC decoder, or DC shorting plug now has 2 rows of 6 pin holes. The extra pin holes are for connections to the speaker, cab light, and a potential strobe light. The DC shorting plugs supplied have 2 rows of 5 pins, and must be inserted such that socket pin holes 9 and 10, which are for the speaker, are left exposed.
The first step is to test it to be sure it runs correctly before I mess with it! I bought the standard AC/DC version, which will run on DC with direction sequencing. So I put it on my 4.5' test track, hooked up an MRC 12 volt power supply which I saved from my HO days, and gave it a test. Worked great, smooth and quiet, with directional lights and the cab light on. Perfect!
Be sure to protect the locomotive when you are working on it. I use a cradle made out of 2" foam, and am careful how I hold the loco and how I put it down. The next step is really to remove the shell. This does not require removing the AF compatible couplers, but since I will be installing the (included) 1295 "scale" couplers anyway, I decided to remove them now. There are 4 screws holding the coupler assembly to the truck. I used a Phillips screwdriver marked PH 000x40, and it seemed a good fit. With the screws removed, the coupler assembly lifts off.
There are four screws holding the shell to the frame. They are marked with red lines in the picture. I used the same screwdriver on them, and they came off pretty easily. Its important to have the right size Phillips screwdiver, and that it be in good condition.
With the screws removed the shell slides off easily. Be sure to remove the bottom end of the vertical handrail which goes between the shell and the frame. On my loco it was only glued at the top, so it popped out of the bottom easily. In this photo I have started to lift the shell as you can see by the black line just under the yellow stripe. There are wires between the shell and the chassis, so it won't come completely off.
With the shell lifted off, you can see the two plugs. The larger is for the AC/DC board, and is the one we want to replace with the DC shorting plug. There is no need to remove the plug to the lights and speaker, but I'll remove it so I can take the shell completely off. I used a small flat blade screwdriver to gently lever the larger plug out, doing a little at a time from all four sides to keep it parallel to the socket board. The other plug cab be pulled straight out, but don't pull on the wires. Take your time and you won't bend any pins.
The AC/DC board is quite large, and is held in the shell with 4 or 5 big globs of hot glue. It comes out very easily with careful prying. You don't need to remove the AC/DC board to install the DC shorting plug, but as I will eventually install a DCC decoder I might as well take it out now.
Here are the shell and chassis. Very clean design!
Here's the AC/DC board removed from the shell. Plenty of room now for when I install a DCC decoder later.
Here are the two DC Shorting plugs. The one with the missing pin is for no cab lights. The plug with all 10 pins will give you cab lights whenever the loco is running.
This is the socket board attached to the chassis.The white socket on the left is for the lights and speaker which are in the shell. It doesn't need to be disconnected unless you want to completely remove the shell. On the right is the socket for the AC/DC board, LocoMatic board, DCC decoder, or in this case the DC shorting plug. Socket pin holes 9 and 10 are for the sound card output (speaker wires) if you have LocoMatic or DCC sound, so they are not used by the DC shorting plug.
Choose either the cab light on or off shorting plug, orient it so that the writing on it is aligned with the writing on the socket board, and insert it leaving socket pin holes 9 and 10 empty. The pins on the shorting plug are numbered consistantly with the socket, but the numbers are really tiny!
Here's how the plug should look installed. Notice the board number on the top of the shorting plug is oriented the same as the writing on the socket board. And you can see that socket pin holes 9 and 10 are empty.
Here's another shot of the DC shorting plug installed.
Plug the lights/speaker plug back in (it only goes one way), reinstall the shell, and you are ready to roll! The SW-9 will now reverse direction with DC track polarity. Remember, this is DC only, not for AC!
Any additions, corrections, or good ideas, send them on and I'll be glad to include them.
Bill Clark
billclark424@gmail.com
