I have been running my 624 and when it was working, two things I noticed during operation was the eunit would sometimes cycle at random, and the pickup rollers would sometimes get hot after running it for hours. A week ago I was getting my 624 back on the track and the engine started making a faint weird noise, the 2 lights wouldn’t shine, the engine wouldn’t run and a lot of sparks flew when I tried moving the engine with my hand. Then the transformer started tripping. I lowered the voltage all the way down and checked to make sure all the wheels were in place and they were, I flipped the engine over and the pickup rollers were really hot! I put the engine back on the track making sure all the wheels were on the track correctly and applied power and got more of the same. I took the shell off and took the pulmor motor off and took two leads from the transformer to the two brushes on the motor and it made a loud hum, but wouldn’t move. I removed the old grease and lubed the motor truck and the motor hole and tried again this time the motor moved a little bit but was pushing up still humming loud. Is it possible I have a bad motor? Or could the short be from the e unit or the pickup rollers? All the original wiring appears to be good and the  solder joints are tough.