It seems that any brass locomotive may suffer from cold solder joints. When baked in the oven, the parts don't usually get hot enough to fully melt and flow the solder paste. Instead, the solder balls sort of cling or congeal with each other in a weak mesh. The result is a dark gray matte mass instead of shiny smooth solder.
Both David and I have had solder failures on Henry Bultman's Car & Locomotive Shop RSD12s. Both failures were of truck side frame equalizing hangers on which the spacing block let go of one or both of the equalizing arms. The result was an eventual short circuit to the rail. Examination revealed that there was insufficient solder wetting on all surfaces of the 3 soldered parts.
Years ago I tried to repair my unit, but gave up in frustration. David's recent request to fix his RSD12 sent me back to work on mine first, on which I was willing to make more mistakes than on his locomotive. Time must have taught me something as my first effort was successful.
I've learned a few valuable lessons watching a fantastic retired modeler Jack Heier. He taught me in a soldering session the importance of making jigs and fixtures to hold everything brass in tight register before adding the heat. I can solder electronics including small surface mount parts, but this was a
duck horse of a different color.
First up, David's lame
duck truck. The problem occurs just to the right of the leftmost or #1 axle wheel. One side of the spacer solder joint completely failed and allowed the outside equalizing hanger to break free.
Next, the two brake hangers are in a sandwich with a milled aluminum spacer that keeps them parallel. Lots of T pins driven into Micore hold the two hangers in what will eventually be vertical alignment. They have received a generous coating of PBL 50-50 solder paste after being cleaned with a wire wheel. I used a PBL HotTip resistance soldering station with their carbon tip to make the joints, cranked up to 4 of 5.
I didn't take a photo of the final repair on David's RSD12, but here is the final result on mine. The brown stains are from clear coat that burned under heat. I dunked David's equalizer hangers in lacquer thinner and wiped them down. They didn't discolor as seen here.
Film at 11:00.
