[Coco] Bad controller

[Bill]

I have what I believe is an FD-500 controller, and when I plug in the drive
cable, it lights up the first drive. If I reverse the cable, it lights up
BOTH drives.

Regardless of which DECB chip I put in, it acts the same. The only other
socketed chip is marked:

WDC '83
WD1773PH-00
8424 02

Could that chip be the problem, and if so, does anyone have one they would
let go of?

Thanks