83 Excella 31 control panel question

[Ebh05454]

I am the new owner of an 83 Excella center bath. Everything is intact and in good original condition. Replacing water heat. The control panel over the sofa works and indicates levels correctly. The ac indicator lamp and the digital clock don’t work. Are there any circuit diagrams available ? Wondering if it is just a cold solder joint. How to remove (carefully of course) to troubleshoot. Don’t want to disturb working components and the wiring harness to the sensors.
Thank you in advance Eric