Yamaha DX 7 battery problems help

Hi !
I got a DX 7 from a friend, and he got a problem with it. It was many years ago on a gig. The DX was connected to a wall mounted power supply socket with a variable
voltage. In Norway it is 220V. But perhaps it was as low as 100V. Well,the problem started then.
I’m not a hi tec.with electronics but i have a friend who are. This is what we’ve done
so far : 1 Replaced battery with a CR 2032
2 Checked power supply, every thing is ok, both voltage is ok.
3 Checked diode D4 is ok.
4 Replaced new ic’s nr. 20 and 21. Think this is the Ram chip’s. It was after
talking to a guy who ment thoose were the problems.

But still the " REPLACE BATTERY " shows when i turn the synth on.
I haven’t checked the IC nr.19. it has the same nr. as no.20 and 21 but i don’t know
what that IC is doing.

Is there anybody there to help me solve this problem i’ll be very thankful

Best Regards

Good morning !
Since you have changed the CR2032 battery and you still have the “Replace Battery” message, you need to start by checking the voltage at its terminals.
If the battery has drained again, it can only be in the 3 RAM circuits, IC19, IC20 and IC21. If you have already replaced IC20 and IC21, you should try replacing IC19 as well. Otherwise, all that remains on this circuit are the 2 transistors Tr1 and Tr3 and the 10µF/16V capacitor.
If you can check these 3 components, it’s easier than changing the RAM, start with that.

Check this and come back if the problem persists.