Anyone familiar with the inner workings of Colour Laser printers. It's and HP CM1312 nfi

I can't print out any reports, only because they are so faint, I can't read them. It appears that CMY all are printing ok but Black is very faint although it appears to have about 1/2 the toner left. It's been slowly getting worse and I've just not had the time, or the motivation to attend to it before now.

Sometime in the past, I think I diagnosed an image transfer belt as the issue, but, did not come to that conclusion today.

So, any suggestions would be great.