Mersedes a140 (1998) diagnostic equipment

I ave a Mersedes a140 from 1998 (european) with a SRS warning light on. I want to find the fault with the system and if possible repair it myself (I'm good at fiddly repairs--I repair mobile phones). What I don't have, and don't seem to be able to find, is a reasonably priced diagnostic instrument that works for my vehicle. Can anyone help me out with this?