Dear TM,
Your SD-90 has two middle rail roller pickups for power, one under each of the trucks. One of them is not working properly.
1.) Turn your loco upside down in a foam cradle (to protect the finish). Check to see that both roller arms (and their roller axels) are well centered, not hung up and have equal "springiness". Check to see that both rollers roll smoothly and freely, and have no flat spots or grooves worn into them.
2.) Use the two track power wires from your power pack to power your upside down loco.
Set the power pack to a low speed.
Touch the end of one wire to a wheel, and the other wire to a roller pickup. The reverse unit should respond, cycling the loco through its forward-neutral-reverse-neutral pattern. Do the same test with the other pickup.
Report back your findings. (More tests/repair suggestions to come.)
Sincerely,
Joe Satnik
Your SD-90 has two middle rail roller pickups for power, one under each of the trucks. One of them is not working properly.
1.) Turn your loco upside down in a foam cradle (to protect the finish). Check to see that both roller arms (and their roller axels) are well centered, not hung up and have equal "springiness". Check to see that both rollers roll smoothly and freely, and have no flat spots or grooves worn into them.
2.) Use the two track power wires from your power pack to power your upside down loco.
Set the power pack to a low speed.
Touch the end of one wire to a wheel, and the other wire to a roller pickup. The reverse unit should respond, cycling the loco through its forward-neutral-reverse-neutral pattern. Do the same test with the other pickup.
Report back your findings. (More tests/repair suggestions to come.)
Sincerely,
Joe Satnik