HP 147a Bläckpatron

We have recently purchased two of these cartridges and the print quality has been very poor, with all pages displaying a dark streak to the left of the paper. The printer was thoroughly cleaned, as was the toner cartridge and the printer cleaning maintenance was carried out as per the advice on the HP support pages, but this made no difference. It was found that there was an accumulation of toner on the 'green roller' at the rear of the cartridge. The roller was thoroughly cleaned, but it was noted that after each full revolution, fresh toner was deposited upon it. This is effectively £300 worth of toner wasted, as it is past the return date. Not great