Today, she's fixed.
The main brake pick command from the HCB drive board to the main brake power supply wasn't turning off all the way, just going sorta "brown". On a good car, it drops to 0, but with this bad drive board, the pick command voltage wouldn't drop off to absolutely zero, rather, it hovered at about 18 volts. It was low enough for the main brake power supply to "eventually" turn off, but it wasn't shutting off it's output quick enough. Which is why the main brake was staying picked for just a few milliseconds too long, allowing the roll-up, and subsequent releveling failure.
The pick/drop command really just "browned-out", rather than going all the way to 0 quickly. This adversely affected the timing of the brake release.
When you are troubleshooting, we tend to think of things as basically working, or not working. One might assume the "pick/drop" command was fine, since the brake was indeed "picking", and "dropping"! Many of us turned our thoughts to other possibilities. But it was the quality and characteristic of this signal that caused the problem. The scope helps to see signal timing relationships and voltages very plainly, which is why I trot it out, when something weird is kicking my butt.
The shorted motor (original problem) put a ton of stress on the drive. I don't know if you read my thread on that issue, but it was turning on and shutting off with rapid, high-current pulses. It was alternately turning on and shutting off on max current limit, protecting itself. Only this happned very rapidly, like a jackhammer. The drive was not designed to endure such a high-current, high-heat duty cycle, not to mention the current spikes and emf it caused. Punish a drive that way for a while, and it will have some kind of failure. Abnormal conditions would definitely include a shorted motor!
It actually ran for hours and hours before a troublecall was originally placed. This heated up the motor, heated up the drive cabinet, and took out the HCB board. That is beyond is design parameters. Before the motor issue, there was not a releveling problem on this car. Only after the motor issue was resolved, and the car turned on for the first time, was the issue with the HCB revealed. We couldn't check for that, nor evaluate the drive in any way, without a good pmsm motor to drive. So this is how latent issues are progressively revealed, after a major issue like a shorted motor has occured.
Last edited by Vic; 05/18/12 01:06 AM.
