Just enough space in this lovely model to fit Zimo MX648 sound decoder and SugarCube7 speaker, to great effect...
Remove body, revealing 6pin socket
Take out socket board and plastic mount to make space for decoder and speaker. Also removed pair of supression capacitors hidden beneath motor.
The Decoder is fitted on top of the gear housing, which was filed a little flatter to give a more stable fit and also a tad more clearance from the top of the body.
Neatly placed MX648 and SugarCube7 in the created space.
Photos courtesy of Ivan Gale
Donor model... great feel, nice and heavy, lots of detail - good job Bachmann and Model Rail!
2 screws removed and the chassis drops out of the body easily enough... reveals a compact 6pin DCC board/mount.
Remove the DCC socket, as well as the PCB that holds it, then chop off the plastic mount so we have a large (chuckle!) flat platform
to play with
We're going to make use of the excellent Zimo SACC16 stay-alive board to attach a couple of Tantalum capacitors to our MX648
sound decoder. Fantastic design, the SACC16 can be used in a variety of ways. Our Tantalums are 330uF flat ones, and don't fit
on the SACC16's pads directly (which are designed for 220uF), so we cut the SACC16 down to just the components section. This will also make the
whole board very easy to find a home for. We've shown the taller (but narrower) 220uF Tantalum here for comparison too...
Next we prepare the MX648, removing the unwanted wires (WHITE, YELLOW and BROWN will not be used). We also add an extra pair of wires
for the stay-alive connection (an extra blue one for +VE and another grey one to the GND pad). When done, recover in Kapton tape - which
also has the benefit of being thinner than the original heat-shrink so will fit in more easily!
Wire up the SACC16 board and the Tantalums (in parallel) ensuring polarity is correct, and protect in some thin Kapton tape. The pair
of Tantlums, which gives us 660uF in total, is not huge in terms of backup power, but it is enough to make an obvious difference to the
running of this model - far less likely to stutter, stall or give sound break-up, so well worth doing.
Next, prepare the motor, by removing it and taking out the existing supression components. We will solder the deocder's ORANGE and GREY
wires direct to the motor.
Now we have the SugarCube7 speaker soldered in too, wires not too long, as we've got to tuck them all in somehow!
Speaker at the front cross-ways, the SACC16 PCB veritcally just behind it in front of the motor worm housing, Tantlums neatly on one
side, and decoder on the top. Actually very neat if you have made the wires a good length!
I was expecting it to be harder than that, but because it came out so neat, I decided to add in a firebox glow light too. Remember we
left the original BLUE +VE wire and the GREEN output wire on the decoder earlier, so we get to use those now.
A couple of screws out from underneath and we carefully prise the cab upwards and away, giving us easy access. Add some weathered
crew figures, and drill a small hole to poke a tiny Nano SMD LED (orange) for the firebox glow. The bulk-head is plastic in this model
so it is quite easy, and we create a shallow channel behind and up inside the loco's body to run the LED's wires along. We need to include
a resistor on the +VE side of the LED back to the decoder's BLUE wire, but there is still a little room remaining on the right hand side
of the motor worm, so it goes in fairly easily.
Carefully put the body back and and hey presto, we have a sound-fitted, firebox glowing, staying-alive, manned, SR USA Tank!