Saturday Service Call to Glenmoor Golf Course
Saturday morning at 8:00 AM, I drive to the Golf Course because the main pump VFC for the watering of the course is down. It didn’t display anything because the Keypad was blank. Due to this, we had no fault diagnostic.
I first verified that the power was off. Then I did an ohmic check of the Input Rectifiers, the Transistors and check the Personality boards.
I then did a visual check of the Capacitor Bank. All looks good so far. I ohmed out the coil on the Pre-charge Contactor…. it looks good.
I visually inspected the Control Board and it all looks good. I visually inspected the backside of the Keypad and it looks good as well.
So what has happened? Then it dawns on me, Pre-charge Resistors. Sure enough, one of them does not read through. It had opened in a small spot and these are connected in series so no power was being applied to the bus.
Now, seeing this the first thing you would think it that the Power Board Transistor failed and dropped the Contactor. When this happens the current flow to the capacitors is across the resistors. So is the Contactor bad as well? Not usually unless it is in a very dirty environment and even at that, it usually just needs to be cleaned and it can be put back into service so long as the coil is good.
So I change the Power Board and the Pre-charge Resistors. Funny thing, the Power Board later checks out okay. So what happened?
This customer turns the VFC off when not in use. The constant cycling of the power is probably enough to weaken the resistors as the resistors are acting as the “Shock Absorber” of the system when the power is turned on.
I have only had one other drive do this so it is not common but well worth noting I think.