Uniden PowerMax 5.8GHz suddenly died?

Sorry in advance as this is long. TL;DR: Broken answering machine. Anyone with experience fixing these or referrals to someone who does would be amazing!

Client brought this to me. This is very important to them as it has the last recording of a loved one's voice on it. It is approximately 20 years old and suddenly died overnight.

I have never worked on an answering machine before but I promised them I would do my best. I've disassembled it (after some difficulty) and can't find anything obviously wrong. No blown caps, no burnt resistors. no cracked solder. Nothing that is jumping out at me as "likely the cause of a problem".

I tested the charger. It claims on the converter that it is a 9v block, but it is outputting a steady 11.6v. I do now know if this is a misprint or what, but it was a stable and steady output and the client had it plugged in for 20 years without issues. Charger block does not get hot or make any coil whine.

Power gets to the circuitry. The medium sized, darker green/yellow board (for easy reference, "power board") holds the DC jack as well as the phone jack. The larger, lighter green board ("main board") holds the screen, and a couple of ICs of what I am assuming are the processor and digital storage. I do not know what the smaller, dark green board ("side board") with the massive shield on one side and almost nothing on the other side is for. For context, the side board is mounted directly behind the phone cradle that holds and charges one of the wireless phones.

To remove this from the plastic housing, I did have to remove the speaker (soldered to the power board), as well as de-solder the 2 wires you see that lead to the handset charging dock. If I know anything about speakers, the unit should be safe to test without the speaker wired in, and the charging dock does not form a circuit without a phone on it so the same should apply there. Other than that, I have not changed or altered anything on these boards in any way.

It is not just a failed screen issue as when it was brought to me no LEDs light up, no buttons do anything. There are no external signs of life.

When tested, 11.6v getting to the power board via DC jack. Power board is delivering 11.6v along 2 lines to the main board, as well as a few select lines that have steads voltages from 0.2v to 1.4v, and a few grounds. Power board does successfully redirect some of that power to the side board with a range across lines from 0.5 to 4.1 (including 2 ol' reliable 3.3v lines).

Based on main lines, so far as I can tell, all the power is flowing where it needs to go. But... the device is not working. Other than just randomly testing every component, I don't know what to do to try and find the problem...?

I'm a bit over my head here. If anyone has experience working on answering machines, or just knows of someone who specializes I could send this off to, that would be amazing.

The device itself doesn't actually matter much. As I said, the recordings on the device are what is important to my client. As such, if anyone knows a way to access the data IC (I am pretty sure it is the one labeled ATMEL AT45DB321B TI 0534. It is 32mb flash storage - https://media.digikey.com/pdf/Data%20She...) and just extract the audio files and put them onto a USB or whatever for my client that would still be a major success. I found the datasheet on Digikey but that is beyond my ability to understand with my skill level. (It is possibly the labeled Uniden UC2881A THAI 5415B01, though based on placement and surrounding components, I think that is only processor. Searching this IC produces exactly 0 results, so I can't be sure what it is.)

UPDATE July 18th 2023 - Photos as requested by Old Turkey