First at all: thanks for your time and help!
Yes, I’ve powered the motors with the CW-80.
The other 3 Engines I’ve mentioned are Lionel too (all steamers) and make it work in the same conditions: fast track with the CW80.
Electricity here is 50 cycle.
Well, okay. I have to admit that I'm stumped. When the loco sits there and buzzes while the loco is on the track and A.C. power is applied, that might indicate one of two things - either the circuit board is bad, or the 50 cycle current is somehow affecting the circuit board.
If your 3 steamers all have Pullmor A.C. electric motors, they most likely would run just fine on 50 cycle or 60 cycle current. On the other hand, if one or more of your steamers has a D.C. can motor, it will also have an electronic circuit board to control the motor. And if they run just fine with your CW-80, I would be even more inclined to suspect that your GP-38 has a faulty circuit board.
However, something very funny is going on. Not sure how D.C. can motors, when hooked directly to an A.C. transformer, ran perfectly good. Doing some quick research on your GP-38, the electric motors are indeed permanent magnet D.C. can motors, and as far as I know, there is no way they should be able to run at all when hooked up directly to A.C. current. If you hooked up your power to the circuit board and merely THOUGHT that you were powering the electric motors directly, maybe the current was still feeding through the circuit board rectifier and converting the A.C. current to D.C. current and allowing the motors to run fine. If that was the case, then this would lend credence to highly suspecting a bad circuit board.
Well, this is about the best I can come up with. I'm not an electronics expert by any means, so it looks like I will have to bow out here. Perhaps someone with more electronics experience can chime in with their thoughts. Hopefully Dub or others will see this and chime in with any knowledge they may have. I hope to see a solution soon, and see if maybe I am more or less on the right track in my thinking.