The fax is printing dark black all over the page

First things first. Try and print report from the fax. Any kind of report. If it is printing OK, then the next step is to check if:

Your clients receive your faxes OK? If they are dark as well, then your scanner head is at fault.

When you make Copy on your fax and it prints dark it could be simply set with dark settings _or_because of the white calibration strip or roller being soiled or dirty, which acts as the ultimate white reference point for scanner _or_ the Scanner CCD sensor is in paper jam release position (too far away from reading the originals) just pull it back to normal feed position.

Or simply faulty scanner.

we will reply u soon...

hello, if you have already cleaned the contact image sensor, or cis unit, its located between both rollers when you lift up the top cover that has the buttons on it. sometimes, this cis/contact image unit fails, and will need to be replaced.

hard to determine the problem without any make/model of your fax machine. However I would begin by looking at the fax contrast and darkness settings, they are likely cranked to the dark side. If you cannot find these settings or this doesnt help. post your make/model information. I don't believe this should affect sending faxes, its likely just a print / contrast setting for received faxes.

change the ink cartridge & get your printer serviced

Where the original page that you wish scanned/faxed there will be a device called a "scan part". This device "reads" the paper to be faxed/scanned as it passes. It usually is found very near where the paper to be faxed goes in.
If there is a spec of debris on this part it will cause a fine line straight down the document. If its dirty, the document will be too! Just give it a good cleaning and you should be fine.
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Thanks
Len

yes indeed. i'm sure by your symptoms, thats what it would be.

Have you tried a new GENUINE Panasonic Toner Cartridge?

If the print can be rubbed off then this suggests the fuser unit is not working correctly. It could be that the thermistor is covered with toner and making the machine think the fuser is hot enough when it's not.

The black line could also be caused by the fuser if one of the pick off fingers is coated with toner or has worn into the Teflon of the roller.

Does the machine show the lines when you print a page from memory - such as a counter or config page? If not, this would suggest the optical path is dirty. Try cleaning the glass and look at the mirrors inside the scanner to see if they are dirty/dusty.

Are the problem prints all from the same source? If so the problem could be on the transmission end. Can you connect to your fax and print to it from a local workstation? If so print several images with dark solid patterns and see if it is actually the printhead. Try printing in cyan, magenta, yellow, and black colors to to rule out each individual printhead.