Hello everyone. Having a very annoying issue with a Gamma D we picked up a few months ago. At first it was an intermittent problem with the F21 fuse blowing but now the car won't hardly run at all even on controller inspection. Most recently I added a circuit breaker panel to the system and branch circuits on the primary & secondary side of the main transformer. I discovered that the primary side of the transformer being fed with the F21 & F22 fuses is drawing 34 amps when the car is trying to run. Both F21 & F22 fuses are balanced in terms of amperage but only the F21 fuse is blowing, both fuses are 8 amp time delay. Collectively the secondary side of the transformer is only drawing slightly under 6 amps when the car is trying to run. Megged the transformer thinking there was a short but every tap read open to ground on 500V scale and no windings are shorted together. I have only been able to run the car 1 time and that was when I drifted it half way up the building and when I took the car off of controller inspection it recovered to the bottom floor. Every other time before the car was sitting at the bottom and we were trying to run up. Going back to the building today to check some more things and will definitely try that scenario again to see if the issue is directional. What doesn't make sense is why the F21 fuse is drawing the amperage it is but it is feeding the primary side of the transformer and not in the motor, thyristor, filter portion of the controls. Wondering if maybe a thyristor gating problem in the up direction vs the down but I will try and confirm that later today. Still doesn't explain why that particular fuse blows unless maybe related to that particular phase of power? Anyone have any ideas or insight I'm all ears. I attached a copy of the print for reference.
Every time I’ve encountered something like this I’ve found some fuse downstream is the wrong size or type. Every circuit coming out of that transformer should be fused or have a circuit breaker. And remember to convert to Volt/Amps (watts) when comparing current draw on the primary to current draw on the secondary.
Ok, so finally got this one figured out. Confirmed the car would run in the down direction perfectly fine. Long story short found the ribbon cable loose on the trigger board. That must have been drawing down phase A and causing fuse F21 to draw excessive current and blowing the fuse. Car is BIS and working fine. Had to install some shim to the retainer for the ribbon cable connector. Seemed too loose.
