[COPIER SPECIALISTS]

I have purchased about 15 Samsung SCX 4521F multifunctions for suppy to various customers. The start-up cartridge is supposed to make about 1000 copies and then call for toner. The next cartridge should make 3000 copies before calling for toner. 4 of these machines have called for toner after 500 copies (start-up cartridge) and after about 1500 copies (follow-up catridge) I have taken the first two back to the suppliers representitives and after 3 weeks had some "board" replaced under warranty. As this MFP does not measure the toner, but counts the copies this creates a mega problem from my customers who land up with half full cartridges. Any solutions, as I can not afford 3 weeks and a lot of carry in expenses to have the problem sorted out when noticed 500 copies later (usually by the customer) and I cannot make 500 copies every time before supplying to the customers! Please Help!!!