Thanks so much everyone - it is indeed a 2836-2 I can see it engraved on the back as mentioned - now i feel a bit silly!
Its stopped working so i plan to replace it with a an ETA or its clone - I assume its not worth trying to get a clone fixed??. I am searching the forum for a good guide but haven't found anything specific to the 2836 yet - meanwhile, if anyone can point me in the right direction, i would be grateful.
cheers