Bachmann "starter set" controller (36-560)

[ejstubbs]

I have one of these controllers and, while I have no complaints whatsoever with its ability to control my locos, the connection from the controller to the track is giving me problems.

 

The controller is supplied with a 2.5mm jack plug and a length of (rather thin) red twin-core flex to connect to the track.  For various reasons I wanted to use my own plug and flex but it seems that the controller is rather fussy about the plug.  A standard 2.5mm mono jack plug from Maplins fits in the socket and sends power to the track, however the plug is a little insecure in the socket and if it slips out by just a tiny bit (less than 1mm) then the loco starts buzzing and goes nowhere.

 

Another connection I made using a right-angled 2.5mm stereo plug (with the correct contact wired in, based on side-by-side comparison with the plug supplied by Bachmann) refused completely to stay in the socket reliably.

 

Although the 2.5mm plug from Maplin works OK, it's annoying when it does slip loose every so often.

 

I have have been considering hard-wiring the flex into the controller - with suitable strain relief - with a plug on the free end and a socket on the baseboard which would transfer power to the track.  However, when I had a look inside the controller to investigate the viability of this idea, I found that there are three connections to the power output socket, rather than the two I expected to find.

 

Before I start de-soldering the socket from the board and/or experimenting with a multimeter, can anyone suggest why there are three connections to the socket rather than two?  It doesn't seem logical, given that even Bachmann's plug and flex only have two conductors.  On the other hand, if there is some other circuit switched in by the plug going in to the socket then that could explain why the loco buzzes if the plug comes adrift, rather than just stopping altogether.

 

Anyone have any ideas/suggestions?

[Judge Dread]

If memory serves, the Bachmann controller has a stereo plug supplied but the "red"cable used would only be mono. Why? I don't know but it is. I have always left this arrangement alone (it's moulded on anyway) and extended the said red cable with a suitable inline plug/socket arrangement if required.

I hope this helps.

[HeeleyBridge]

Just checked in the cupboard. The plug on the supplied cable is a standard 3.5mm Stereo Jack.  I assume that the corresponding stereo socket is used, hence 3 connections. Without taking mine (actually my granddaughter's) controller to pieces, I can't tell you how it is wired.

[smokebox]

I don't know about this particular controller but often all 3 of the socket connections are used on various circuit boards to make the socket as mechanically secure as possible to avoid damage when the plug is inserted and removed, even though electrically the 3rd connection may have no function in the circuit.

[Suzie]

I suspect that the extra connection might get used when the controller is used as a slave with the E-Z Command DCC controller.

[ejstubbs]

Oh dear, it seems that my recollections when I wrote my OP were not as accurate as they might have been.  The plugs are, of course, 3.5mm diameter, not 2.5mm.  The Bachmann plug is a stereo one, and so is the Maplin one.  I now remember that it must be a stereo plug because the Bachmann track flex is not wired to the tip connector of the plug, just to the two 'inner' ones.  Thus a mono plug will not work - in fact it will short the controller output.

 

I think the unreliability of my Maplin plug is down to tiny dimensional differences between the two plugs.  At least now, if I do decide to re-engineer my controller's connector, I know which of the tracks on the circuit board I would need to solder the flex to, based on which of the contacts inside the socket they are currently soldered to.

I have always left this arrangement alone (it's moulded on anyway

 

And that is the core of the issue I have with this controller.  IMO moulded-on plugs are a failure waiting to happen, and I thoroughly dislike the thought that I might not be able to effect a repair because it required a strangely non-standard part.  Luckily, though, that seems not to be the case (although the socket Bachmann use does seem to be rather fussy about the precise dimensions of the plug).