91 usually has to do with player tracking and remote host comm.
the "ff" is not found in the manual.
Make sure when you put the mains back in that you didn't bend a pin, also, another trick is to remove the two RAM chips and and swap them with each other.
Yes, after all of that, do another clear.
I attached a layout for the power supply, make sure your 5 volts reads 5.16 VDC with power on and everything plugged in.
If not you can remove the power supply from the back wall and with power on and reading the 5 volt adjust the power supply with a small screwdriver.