Some of the new BLI M1 A&Bs just released exhibited intermittent shorting such that the DC or DCC power source would shut down. We initially determined that by disconnecting the draw bar the short would be eliminated and that in some way the tender was responsible.
Bob Liberman did some digging and determined that the volume control potentiometer was impinging on the top of the reset jumper assemply, thus causing a short. The remedy is to apply insulating tape to the bottom of the trim pot.
The pictures show how:
1) Reset jumper plug is at lower left corner of circuit bd. near mounting screw, to the right of JP-1
2) Shows bottom of trim pot assy inside upper tender shell.
3) Shows Kapton Tape added to bottom of trim pot assy.
A simple alternative to returning the loco.
Comment added 4/20/2004
“Saw the suggested fix for the volume pot shorting to the reset pins. Although the application of Kapton tape is a good one (we use Kapton tape extensively where I work), the insulation provided by the tape can be temporary. The speakers are vibrators and there is probably some slight added, hardly noticeable, vibration from the tender trucks when the locomotive is moving. The Kapton tape can wear through, especially if the parts of the volume pot and/or shorting plug have sharp corners.
Yes, after applying Kapton tape to the pot on the tender on my M1, the short did reoccur after approx 15 minutes of running. The clearance between the pot and shorting plug can vary and in my M1, apparently, it is an interference fit and reinstalling the tender shell (with screws) put them in ‘intimate’ contact with each other so that the tape fix wore through. Being very careful, I was able to bend the shorting pins sideways approx 15 degrees to increase the gap between the pot and shorting plug. Have not had any problems since.”
Don Luke Tucson, AZ