I've removed the Auto-Bias PCB V1.3 PCB from the inside rear panel of the chassis and installed the V1.2 PCB I had tucked away. Hardest part of changing that board out is getting the tiny flexible circuit from the LED Display assembly to plug back into the mating connector at the bottom edge of the Auto-Bias PCB.
Powered up the amp, and it behaves just the same as the one I removed. It will bias up from a cold start, but, will NOT return to stable LED status once you've switched back to Stand-By and back on again. I've also found that the Manual Up/Down buttons which allow you to decrease or increase the nominal plate current level from the factory default level. I went and powered back up from scratch, since nothing works with this Auto-Bias circuit once you've entered & left Standby mode. When the amp was thru setting the Automatic Bias from the cold start, the Manual adjustment keys WILL NOT CHANGE the bias level AT ALL.
I swapped out the 12AX7 input stage tube of the power amp on this T-shaped chassis, but of course, that made no difference either.
My life feels so much better knowing Fender has installed a computer-controlled bias circuit in these amps!