OP here. "It's fixed!!" (kind of -- see below). I said:

Does anyone know how to dismantle a Bosch hedge trimmer?
I have an AHS 55-26 trimmer -- a superb machine. However it stopped
working the other day - dead as a dodo (and no traumas such as being
dropped). I've had it 3 years; it gets pretty heavy use.
Funny thing was, when I plugged it in to try it again 2 days ago, it
started up fine. I went to the hedge, started cutting, and a minute
later it stopped dead again (btw: the cutters are _not_ jammed).
I decided that maybe the brushes need replacing, so set about taking it
apart. (I have an exploded view from a spare parts dealer's site)
It's looking impossible, so far, without dismantling every single
component of it. And in any case I'm now stymied by a circlip which is
holding the cutter assembly in place.
I will ask a mate if he has circlip pliers (?), but meanwhile: has
anyone here done this? Is there "an easier way" to get at the brushes
(which I can almost see through the vents).

It's extremely frustrating...I had exactly the same
thing happen to me on my previous trimmer, which was exactly the same
model, and was also 3 years old at the time. The remedy then was to buy
_this_ one :-(

Well: a qualified "it's fixed!!" -- through the well tried and tested
method of taking the thing apart, looking at it, poking it, blowing the
dust off it, shrugging in mystification, and then putting it back
together.

By far the biggest challenge was getting it apart; there's nothing in
Google/Youtube for dismantling this particular model, although I could
garner general hints from one or two of the hits that there are, for
"hedgetrimmers".

I have the advantage that (as explained above) I have *two* of these,
the first one having packed in 3 years ago. So I used that as a
potentially sacrificial trial.

Today I actually, finally, managed to disassemble it. I bought some
circlip pliers: they were too big (thanks to Homebase for giving me my
money back, no quibbles). *Then* I discovered, through desperation,
that I could get the circlip off using my Swiss Army knife.

No more details about disassembly - let me know here (_not_ via email)
if you want to know more.

I discovered that the brushes are in fine fettle - only about 1/4 worn
by the look of them (after about 3 years' hard use). So why the hell did
it stop?

I'm not any kind of electrical fellow, and so have no circuit testers
etc. I just poked the switches that I found, and eventually decided that
*maybe* the main ON switch (the big orange one in the handle) had lost
its alignment with the tiny electrical switch that it bumps, when you
squeeze the handle to start cutting. But hardly likely, I figured. But
anyway ...

I half-put it back together again (without the blade assembly, and not
entirely screwed up), and squeezed the handle: for the first time in 3
years, it burst into life. What's more, once I'd put it all together
properly, it *still* works.

The biggest win here is not so much that it works again, but that I now
know how to take one of these apart, and with confidence.

I hope this was of some interest to one or two!

Cheers
John