Philips PM2421 chopper amp schematics

[RikV]

I acquired two Philips PM2421 DMM's. As far as specs are concerned these are poor (max 1299 counts,mlax voltage range 300V DC/AC). But they have a nixie display and are of a nice construction. Anyway, i'd like to fix them.
Documentation is not hard to find but as often is the case: there are different versions of the aparatus! the ones I have are PM2421-08 and PM2421-41, whatever that means. Unfotunately all manuals on the www that are readable concern version PM2421-01! I found one correct manual (manualsLib.com) but élas!! schematics are blurred to the extent of being unusable.

Is there anyone out there having a manual (PDF)  that is usable? The references on the one I have are:
9447 024 21..1, 9499 470 09301, 741115/08/09/41.

Side note: is there any logic behind the numbering scheme used by Philips?