Thank you gentlemen for your information and advice. It turns out that the problem was with the 8-pin socket in the light board, which was identified as a problem area in the earlier versions of the Bachmann gas electric. The instructions for correcting it suggested cutting the incorrectly installed trace from pin 3 to pin 7. However, the decoder I was installing had no wire to pin 3 and so would not have been causing the short. What I did discover upon examining the back of the light board was that sloppy soldering during manufacturing had connected pin 1 to pin 8 on the back of the socket. Of course, this did not show up running on DC but shorted out the DCC decoder when plugged in.
I wound up just hard wiring the decoder and eliminated the socket altogether. Now it runs great.
I appreciate all the good feedback; it led me to the problem quickly.
Please see the following page for an answer to your problem.
http://home.roadrunner.com/~mrwithdcc/doodleb.html
Tom
I have two of these. There is a factory wiring error under the 8 pin socket. I am trying to find the info.
Seems like there was a jumper that needed to be cut out. I will let you know if I find it.
There is an electrical short in your wiring or the decoder's wires are improperly connected. Go back over everything and check your wiring against the schematic that came with the decoder.
The Bachmann's motor may not be isolated from the frame. You need to get a voltmeter so you can check for proper isolation of the motor's brushes and insure that one of them is not connected to the frame.
A "good enough" voltmeter can be purchased from Harbor Freight for as little as $1.99 when they have them on sale.
I installed a TCS DP2X plug in decoder in a Bachmann gas electric. I had purshased the gas electric about 12 years ago so it was an early version. I placed it on the layout and started to program the address when it began smoking. The decoder fried. After receiving a replacement decoder from TCS, I installed it in the gas electric again, but this time used the program track to see if I could program it there. The loco started moving on the program track as soon as I hit enter on my NCE throttle to get into the program track mode. The trottle was at zero. The decoder did not fry. Anybody know what is going on?