I have ordered a pair of primers, forward primer is working well, I have checked it by gel, but revers primer has really weak band in gel, and PCR doesn't work. any suggestion?
do you mean a weak band of the primer itself? Have you checked the concentration by UV-VIS? If the primer is diluted to strong you could just add more to normalize the concentration.
Have you checked primers concentration after synthesizing and further dilution factor is equal as forward primers? if not adjust concentration of Primers up to the concentration of forward primers. Same concentration giving band over the gel than use reverse primers more in PCR reaction (desired concentrations adjusted folds during run on gel), another hand, you can check the concentration of the primers by UV-VIS.