1st series TAC50. Can't get my WDPF output to go high to run unit. Checked capacitors (all at or close 2000 microfarads), Swapped current regulator, QSS/QSR interface, inverter interface and motor IGBT and ribbon cable between inveter and current regulator. Checked all connections. It came up for a few seconds all on it own and did a recovery run but after changing inverter brd it will not come back up. Any ideas or suggestions?

Isn't there a resistor "RSS" right above that cap bank on the right? I don't remember it it's actually on that QSS interface board you're referring to. If it opens...your dead.