As a first step, it would be necessary to isolate the problem, that is, determine if the problem is in the development of the image (where the cartridge, the transfer roller, the laser "LSU", etc etc) or in the fusion, or in both. To determine, I suggest that you carry out a medium print test, the procedure would be: to place a white sheet in the multipurpose tray (front), send a self-report, when the white sheet disappears from our sight, remove the power cable, open the cartridge cavity door, remove it and carefully remove the sheet since the toner has not fused, we observe the impression, and this helps us determine if the quality problem already occurs in the development stage or in the merger, or occurs in the development and is aggravated in the merger. In the market there are many qualities of films, pressure roller, etc. etc. but not all of them work well, on the one hand it must be considered that this model uses a film that is black inside and not ivory in color like conventional ones, the film must be suitable for HP models P2035 / P2055 / Pro 400 and Pro425 On the other hand, the thermistor varies according to the number of copies, so it must be replaced in most cases, or, in any case, if it does not raise the amount of temperature required to merge, you can try to place a wrapper of filmina used, from one layer to the thermistor, as if to move the thermistor away from the surface of the resistor, that way the temperature will increase to a small extent but enough to merge correctly. I await your comment and experience, best regards