Ensoniq KT76 quiet

Hi. I got an old 1994 Ensoniq KT76 keyboard but it’s very quiet. It’s quiet both via headphones and line out. ROM battery replacement warning is on but i don’t think it has to do with it. Something with the amp evidentially. Any suggestions?
Thanks!
Sergei

Been reading some comment regarding other Ensoniq keys that are also quiet, sounds like could be bad caps or poor connections. I’ll start with that. Please let me know if you have suggestions. Thanks.

Been reading here and there about similar issues with Ensoniqs. Looks like might be an amp chip inside. I still have to change the ROM battery, but that won’t have anything to do with being quiet. Sprayed DeoxIT D5 into the volume fader and jacks, no result. Next step is to open up and start poking around.
Question: Does anyone have a service manual or diagram for Ensoniq KT? Thanks folks!