[sdiy] DMM problems [OT]

[Seb Francis]

Hi,

Apologies for this OT post, but perhaps someone can help me out?  My 
Voltcraft VC506 (also the same thing as an Atimco Protek 506) digital 
multimeter has just started giving really strange readings for 
resistance.  All other functionality works just fine, but the resistance 
readings are just plain wrong.

It reads about 500R in autoranging mode and different readings in each 
range when manually ranged (from about 30R up to 20M depending on range).

It's all SM inside, but pretty large scale, and all the parts (apart 
from the big 'brain' IC) look fairly standard.  So I'd like to have a go 
at mending it ... but really have no ideas where to start.  There are 
various trimmers for calibration, but I assume it needs more than a 
quick tweak.

Anyone got any ideas?  Or maybe where I could find a schematic or 
service manual?  Or even a place in UK which would repair it for me?  
I'm loathed to just replace it since it's a very good DMM when it's working.

Seb