More rivarossi Y6 DCC help

[nw-modeling-list at nwhs.org]

Nigel, and anyone else who can help me. If I by-pass the decoder and run the 
locomotives off straight DC, they run great. All three of them. I solder 
into place the decoder, and it doesn't even act like its programming. I 
can't believe I would have three bad decoders, and I had no trouble 
whatsoever putting the same decoder into an old Mantua 4-6-2. I have 
isolated the motor from the frame of the locomotive, have double-checked my 
solder joints.... what am I overlooking? Obviously since they run 
floawlessly on straight DC I don't think its a contact issue. I have four 
drivers on each side picking up current. I am almost to the point where I am 
going to find someone who will put the decoders in for me and test them.
Just as an FYI I have the Prodigy Advance system, and the Bachmann Spectrum 
J, Spectrum K, two Spectrum 2-10-0's and the Mantua 4-6-2 ALL run so 
flawlessly that this has me truly baffled.
ANYONE... help?

Bob Welsh