I may have mentioned this before - here
That bloke is somewhat brave hosting that stuff. A few years ago Garmin sent their lawyers to every site that came up on google which had any Garmin manuals. Many homebuilders who used GNS boxes (mostly Americans) had all the docs on some website which described the project. Most of the people ignored the threats...
Anyway, for electronics anoraks like me it's interesting, but on pages 50-51 (of the PDF) you find the often-asked-for memory battery replacement instructions.
Unlike the mostly very detailed King MMs, there are no schematics and no mention of the processor type. But they seem to use analog circuitry for decoding the NAV/GS signals - no digital signal processing stuff like the Sandel EHSI uses - which does open up the possibility of bizzare failure modes like this.
