Note: The MEC SW-9 Christmas locos have a non-NMRA compliant socket by mistake. There was no way to correct the problem in time for Christmas, so the locos that were ordered for DCC are being held at SHS for upgrade to the compliant board when they arrive, unless the customer asked for the loco to be shipped as AC/DC only. Those locos may be returned to SHS after Christmas for the compliant board to be installed, or the customer can request that a compliant board be sent to him as soon as they are available.
This article is for the person who desperately wants his/her MEC Christmas loco with DCC sound for this Christmas! I fully expect to install the correct board and Tsunami decoder when they are available. This is an interum solution!
This is part 2 of the process. Go to Converting to DC if you want information on removing the shell and the AC/DC board. This article will pick up at that point.
This locomotive, like the Showcase Line F3 and F7 previously released, has a plug which will allow a SoundTraxx sound and control decoder to plug in directly, probably with a special harness. The SoundTraxx package being developed for this locomotive will include the new Tsunami decoder. The problem is the release of the Tsunami has been delayed by SoundTraxx, and it won't be available until at least January. I tend to be impatient, and besides the MEC SW-9 I have is a Christmas Loco. I need it running now!
So I decided to do a custom installation of a SoundTraxx DSX sound decoder with a Digitrax DH-163 decoder for motor and light control.This will be a considerably more complex installation than the Tsunami will be, but there is plenty of room in the locomotive for the decoders, and the fact that the speaker is installed already, and all the speaker and light wiring is in the shell with a plug connection to the main board will make this fairly easy.
The first step is to test the current draw of the motor, to determine the minimum current rating the motor decoder will need. I tested with the DC shorting plug installed, using a 12V MRC power supply and a multimeter. With full voltage from the supply and the loco held in place with the wheels spinning, I read .37A at 11V.this is the highest current I'm liable to see in normal operation. I also did a stall test, which consists of pushing down on the loco long enough to stop the wheels and read the current, again at full voltage. If you do this, be sure to only do it for a second or so to avoid potential damage to the motor. This measurement was .48 Amps. I would feel comfortable using a decoder with a constant current rating of .5A or more. It turned out I only had one decoder in stock with 3 or more functions, a Digitrax DH-163. I needed the extra function to be able to control the cab light. The DH-163 is rated at 2.0 amps continuous, so it should be fine.
There is a removable hatch under the stacks on the top of the loco. By removing it, I was able to measure the clearance from the top of the motor to the shell at 9/16". The DSX is 3/8" thick, and the DH-163 is 1/4" thick, so they cannot be stacked. I decided to put the DSX on top of the motor next to the plug, and the DH-163 further back, still on top of the motor.
One final step before actually installing the decoders is to program them. Its ideal to include micro switches in the power lead of each decoder, so they can be programmed individually. I didn't do that, choosing instead to program the addresses of each decoder before installation. Any other programming can be done in service mode on the mainline. This loco is 335, so I made the DSX short address 33, the DH-163 address 35. Then I made them both long address 335. That way they operate together with no need to consist them, but if they need to be programmed I can set them both to short address then program them individually using the short address, in service mode. In an emergency, such as losing their addresses, I can unplug first one decoder and then the other, as they both have wire harnesses that plug into the decoder.
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I decided to make a plug to go into the SW-9 socket, so that it would be easy to replace with the Tsunami once it is available. These are PCB (printed circuit board) sockets. I have them 8 long by 1 wide. The socket in the loco is 2 x 6, so I cut two of them to 6 pins long, then glued them together with thick CA glue. The pins are perfect as plugs, and the sockets are perfect to solder the wires to. After curing, I ran a #69 drill bit into the holes, to make it a little easier to get the decoder wires in. Actually, since converting to the Tsunami means swapping out the board, it would be reasonable to solder right to the pin sockets on the board and skip making the plug.
Here is the board in the loco. The socket on the right is the one for the decoders. It was meant to include an NMRA medium socket in the middle, sockets 1-8 with the white square around them. Unfortunately during design layout the socket got flipped. If you look at a standard NMRA plug layout, or at the diagram in the SW-9 owner's manual, you'll notice that sockets 1-4, 10 and 11 should be on the left, and 5-9 and 12 should be on the right. This is why there is a "no DCC" sticker on the board. A decoder with a standard NMRA plug can not be used with this board. The DC shorting plugs shipped with the loco are wired the same as the board, so do work in this loco. The LocoMatic boards shipped with the MEC SW-9 Christmas Loco also are wired to conform to this plug layout. If I want to upgrade this loco to LocoMatic, I have to be sure to get the correct LocoMatic board.
This board is being corrected for future runs of the SW-9, SW-8, and NW-2. Extra boards are being made and will be made available for anyone who wants to upgrade to the SoundTraxx Tsunami decoder. There are 6 easy solder points to swap boards, so if you are confident of your soldering skill you can replace the board yourself. If you prefer, S Helper Service will replace the board for you if you return the loco to them.
Here are both sides of the board, so you can see the traces. I spent some time with the ohmmeter, and to net it out, all connections to the plug are as shown in the owners manual, except that pins 4 and 8 (track pickups) are reversed, and pin 11 is the cab lamp. Notice that on the bottom of the board there are resistors in series with the light (LED) circuits. Thus we don't have to worry about putting resistors in the wires from the decoder to the lights. Also notice the 6 wires that need to be de-soldered to swap the board. Looks very easy. But the new board is not ready yet, so I'll just make the adjustment when I wire up my plug.
Here is my plug, installed on the board. I find it easier to solder the wires with the plug installed. The numbers are there to see, the board holds the plug for me, and the sockets act as heat sinks so I am less likely to damage the plastic around the pins.
Red and black wires come from both decoders, so I stripped them, twisted the end of the 2 reds together, tinned them, and inserted the pair into the plug socket. Then touch the socket with the iron and a bit of solder and red was done for both. The same process for black. The rest of the wires were all single, and I worked from one end of the plug to the other, soldering carefully and inspecting each connection to be sure I didn't create shorts.
SoundTraxx requires installing a small (included) capacitor in series with the speaker + lead. I put on some shinkwrap then soldered on lead from the capacitor to socket pin 9, then with more shrinkwrap soldered the other lead to the violet wire from the DSX. The picture above shows the final result. Here are the connections, using the numbers printed on the board:
| 1 Motor - (gray)(label M+ on board) | 7 Lamp Common (blue) |
| 2 Lamp Rear (yellow) | 8 Left Rail Pickup (DSX + DH black) |
| 3 Lamp Common (shorted to 7) | 9 Speaker Plus (capacitor to DSX violet) |
| 4 Right Rail Pickup (DSX + DH red) | 10 Speaker - (DSX Violet) |
| 5 Motor + (Orange)(label M- on board) | 11 Cab Lamp (DH Violet) |
| 6 Lamp Front (white) | 12 Not Used |
After all connections are made, check everything again to be sure all connections are correct, and there are no shorts.
Here is the setup in the loco. The DSX needs to slide forward a bit to allow clearance for the DH-163.
Here is the final installation, ready to replace the shell. The large white decoder is the DSX, the smaller blue one is the DH-163. I used foam mounting tape under the DSX, and electrical tape over the DH-163.
And here it is, cruising down my test track with rear and cab lights blazing!
Remember, if you don't mind waiting a couple of months, the SoundTraxx Tsunami installation will be much easier: swap boards (6 wires) and plug in the Tsunami. But if you are in a hurry, this wasn't bad and was actually fun. It took me 3 hours, including taking the pictures.
If anyone has any comments, corrections, or suggestions, please send them to me!
Bill Clark
