The grid section may be wired to always be on with power, so it could be that the micro is just not running when the rest of the display is blank.
I just grabbed the service manual from Hi-Fi Engine, but other sources may have it too.
Check the voltage to IC401 and also make sure /RST is high. You can find this signal on pin 13 of CN301 (should be on front board). It comes from pin 5 of IC202 on the main board.
Some of these models develop cracked solder joints on the main PCB, especially around the RCA sockets and in the power supply section.