I purchased a used TR7520, and when I started it i got a Code 6004, and couldn't clear it. The Website indicated paper shreds somewhere inside the printer, but none existed. the alternative is to maybe buy a new one at a discount - what! I opened the cover to observe what was happening when I hit the power button, but that in itself is a deal killer. I did however notice that the printhead ink tray seemed to stop mid way in the boot process. Short story is I put a shim in the slot to fool the printer into thinking the lid was closed and observed. The print head wasn't moving at all, thus the error code. Someone posted that they had turned a gear on the side of the printer just a little bit, I did that and the print head was able to move. then I noticed a gummy ink on the waste area where the print head rested. I cleaned it with a tooth brush and IPA, I also cleaned the print head completely and reinstalled the cartridges. Then tried to boot it up again. It worked! I got an error that the rear tray had an open flap or some such thing, but it did boot to ready - no error 6004. I wiped the carriage guide piece of metal with silicon, and attempted to clean the rest of the inside of the printer. I started printing. Some of the ink was blurred but the document I printed was duplex and 5 pages, by the end of the print job all was fixed. Cleanliness is next to "printliness" I suppose. This printer is more sensitive than my grandchildren! But it's a nice printer, and not too expensive.
