it could be an internal fuse,or the power lead is faulty ,try spray the sliders with a circuit cleaner,ipa (isopropyl alchol)the sliders are open to dust and can get contaminated,if you cant get the ipa,try meths ,be carefull take the batteries out when you apply the cleanr,move the sliders up and down to clear the carbon track of dust,hope this helps
mm
July 2012
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