Large Scale Central

Dead End - DCC Upgrade to LGB 20851 Mallet

Hello Fellow Hobbyists - I’m doing a DCC conversion on someone’s older LGB 20851 Two Motor Block Mallet which has a Phoenix Model 97 DC/DCC Sound Decoder previously installed. The person knew he striped the idler gear in the rear motor block during a railway crash, and when I removed the motor, the damaged idler gears were obvious. I’ve done the following: Installed a Massoth XL Power Decoder; installed Massoth DCC Pulsed Smoke Generator; Installed 2 new Idler Gears in each motor block (front motor block also showed some damage too); installed new LGB/Marklin E126050 motors in each motor block which required bending the motor’s electrical pins for proper motor block fitment (see photo); replaced two defective carbon brushes in front motor block.

Problem: The loco’s motor blocks run smooth when operating on my Piko DCC Central Station test stand or when tested with DC power. But when I test operate the loco on my indoor DCC layout powered by my Massoth Command Station/Massoth Power Supply, the loco doesn’t operate smoothly. There’s a slight amount of continual surging noticeable at Navigator speed setting 1, 2 , 3 etc. I took the bottom covers off both motor blocks and realigned the wheels/gears to ensure there’s properly meshing, no binding, and the loco still doesn’t run smoothly. I can’t figure out why this loco isn’t running smooth as silk like all my other locos. What diagnosis am I missing…advice please!

Maybe the loco, with 2 motors, is drawing too much current from your DCC booster.

David - This morning, just to play it safe, I replaced the XL Decoder with another brand new one. The first one I had use some on my test stand loco and maybe had made some CV adjustments to it. I put the loco on my indoor DCC layout for 15 minutes pulling three RhB passenger cars and it ran smoothly…so it was the decoder. But this loco has been run quite a lot based upon the condition of the wheels. So I believe eventually it will need new motor blocks due to the normal wear and tear of the axles and their supports in the motor blocks.