K, back on line..the plane has WiFi and I have a few hrs to kill....LOL
Abt the serial number... The 02xxx+ would have had the changes already made. The 01xxx would have had the bi-polar 4.7uf. The changes were made for a reason. I have seen a 01xxxx very messed up. Yamaha went ahead and improved the protection circuit mainly as well as other areas of the amp.... Like I said, I am not aware of any service bulletins for this amp, but I am certain abt the changes.
Like Avionic said, don't waste that ES, you'll find a better use for it somewhere else.
If you post a photo of the sub-boards / amp boards, I will be able to point you to that other areas of where the circuitry changes were made.