Known working PSU & board, formatter & front panel- Z3200 won't boot, dim backlight in front panel

[kspl]

My PSU & associated board recently started overheating intermittently, so I replaced it with a new one. 

Upon installation, the fan runs and the front panel lights up dimly, but with no beep, text or power button light.  The formatter board was fully seated.  The printer doesn't go through any start-up movements.

I reinstalled the old PSU (which works until it heats up), but now get the same result as with the new PSU.

I have an completely identical, working Z3200 that I can swap parts with for troubleshooting. I've been able to verify that the formatter and front panel are working fine.  

Any thoughts?

Thanks. 

[kspl · Accepted solution]

Update for future generations:  it seems that, despite the obvious color-coding, I had swapped two connectors on the PSU board.  Solved.