A 2kg limit is not much - my Salter scales are battery operated and measure up to 5kg - they cost £15 at John Lewis - Five ranges - Lbs & Oz / Oz / Ml / g / Kg...
Weightwatchers business is not making scales - they will have them made for them - probably in China - and your hope that they must be repairable because of the price paid may be forlorn.
Diagnosis and repair may well be impractical and will very porbably not be cost effective.
Amazon have Salter scales from about £10...
Good luck...
Peccavi
January 2010