I recently picked up a Bachmann S4 #63202, which came pre-wired for DCC and sound as part of Bachmann's DCC Sound Onboard offering. Used engine, but likely never pulled out of the box, runs great. I'd like to add a keep alive, but am unfamiliar with the Soundtraxx decoder included in the unit and can't find a wiring diagram online to reference. I picked up a Sountraxx CurrentKeeper II 810160, hoping that it may be compatible, but not sure where to wire it.
For starters, there's no plug on the board so I'll need to solder to attach. The board looks like this:
The chip on the underside reads Bachmann AE32028
Rather than being soldered to the unit, the decoder seems to be attached to the wiring via plastic clips:
Top to bottom the clips read:
HL+ HL-
S+ S-
RR LR
M- M+
BL- BL+
Any suggestions on where to wire the CurrentKeeper in?
I have two of these Bachmann Sound Value S4 locos and I would also like to fit stay alive circuits but haven't even looked to see whether one would fit. I have added several of the DIY stay alive circuits I built to locos equipped with NCE D13SRJ non-sound decoders and they work great! The blue wire of the stay alive connects to a soldering pad directly underneath the blue wire connection on the JST plug while the black wire connects to an open soldering pad clearly marked (-) on the underside of the decoder.
The biggest problem adding a stay alive to the S4 loco is the fact that Bachmann does not follow the NMRA accepted DCC wire color code making it more difficult to determine connection points. I interpret the Bachmann decoder markings to mean the following:
HL+ HL- means HeadLight positive and HeadLight negative,
S+ S- might mean Sound positive and Sound negative,
RR LR is pretty clear as the Right Rail and Left Rail pickups,
M- M+ would be Motor negative and Motor positive, while
BL- BL+ should be BackupLight negative and BackupLight positive.
A bit of trial-and-error might be necessary but it should be possible to connect the blue wire of the stay alive unit to either the HL+ or BL+ soldering pad as this is usually a "common" connection. Where to connect the negative side of the stay alive is another question. Fortunately, the plastic caps holding the wires to the soldering pads make temporary connections rather easy. Once you find the correct connections, I would recommend soldering ALL of the wires to their respective soldering pads as the plastic caps have a tendency to work loose over time.
Hornblower
I suspect the decoder in question has a small one as it is as I get no interuptions in sound. If I am right could the larger capasitor be put in its place?