Bachmann HO DoodleBug
Decoder Installation [Problem] as of  6-98
by Don Crano

The problem

The NMRA Socket is mis-wired.

I am sure most of you know there has been a problem with the NMRA socket on this Loco since day one. The problem is that Pins 3 and 7 are connected together on the underside of the PC Board. Plugging in a decoder with a NMRA plug, that has a function wire connected to pin 3 and turning on this function will result in this decoder function seeing a direct short between the function output pin 3  and the decoder function common pin 7. This will usually result in this functions output to be blown and no longer usable.  

The Fix!

The Current Fix by Bachmann is no good.

The current fix supplied by Bachmann is a note that is included with the Loco. This is Ok and it does warn you the consumer that there is a problem with the NMRA socket. It also attempts to show you how to correct the problem. Now here is where the problem with the new fix starts. These directions are wrong and will lead to even more confusion and possibly more blown decoder functions. Here is a scan of the enclosed note and hopefully a explanation of what really needs to be done.

Besides warning you of the problem, the only other good advice shown on this note is to contact your DCC Manufacturer. Note the diagram on the right side. This is indeed a proper look at the socket. But notice the area I circled, it is not a green wire as shown. It is a PCB trace on the board. And is the only diagonal trace under the socket between pins. It is easy to spot. The fix is to cut this trace and make sure Pins 3 and 7 are no longer connect via this trace. Actually a very simple and easy fix.

There is another fix. This will leave the shorted pins on the SOCKET, but will prevent any damage to your Decoder function output.  If there is a wire connect to pin 3 of the decoder PLUG, remove from the PLUG. If there is nothing connected to pin 3 of the decoder PLUG you will note have any danger to your decoders function output.
Not all decoder manufactures have a connection to pin 3 on their NMRA PLUGS. And those that do do not always use a green wire. No matter if you choose this fix, just make sure there is nothing connect to pin 3 of the PLUG.

Also to be sure of no additional confusion on this. Please make sure you understand and know the difference between the PLUG and SOCKET. The reason I ask this, it almost appears to be what happened with Bachmann when they tried to explain the fix in the note.


copyright © 1998 Don Crano