Charles is correct. You should check +/- 15VDC especially when you have error message reported - all related to audio.
One of the first thing I would do with any A810 even with younger SN's greater than 5000 is to pull out the cards, remove the basis board from the back, replace all 470uF and 1000uF axial caps regardless. Even the blue Philips caps can go poof all of sudden and the dreaded yellow Frako caps have 100% failure rate.
The caps in the power regulator (Studer calls is stabilizer) board should be next for replacement.
Then, any machines with audio related issue, I would also suggest you remove the tape headblock and get to the repro head preamplifier board. There are two electrolytic caps for +/-15VDC supply for the opamp that need replacing.
Some of the logic problem even after all the caps replaced on basis board could be caused by a filter cap in the operating LED (LCD) panel for +5VDC. It should be replaced as well.
There are many other electrolytic caps needing replacements in cards but that's another story.
In addition, replacing the battery on the all Studer MPU card can go smoothly but after you pulled the old battery, you should examine the areas around the battery for any battery leaks that can corrode way the circuit traces. If the green stuff is anywhere on the chip socket, you must pull the socket out and examine the circuit traces and replace the chip socket(s). I have had the leaked battery chemical that had corroded the chip socket pins so badly, it dissolved metal pins completely away.