Our 1720dn continually flashes, "toner" and "error". A printout states that the photoconductor kit has reached the end of it's life. We have installed a new kit and continue to receive the same message and symptoms.

The drum has come to the end of its life. You should replace the drum assembly and reset the drum counter. Here is the procedure:
power off and open front door
hold down the continue button as you power on printer leaving front door open
when error light comes on release continue and close front door.
toner low, load paper, ready, and continue will all be lit.
press cancel slowly 4 times or until just toner low lights up. each time you press cancel, the light sequence should change
when just toner low is lit, press and hold continue button until lights cycle up and down in sequence.
release continue.. toner low will be lit again
turn printer off, wait 10 secs or so and then back on
press continue button to print off settings page and check under cartridge information, photoconductor value is 0K (zero)

Here is an excerpt I found from the W840 user manual. Looks like you need to change the photoconductor kit. Here is the link for the user manual: images.lexmark.com/publications/pdfs/w840/eng/ug.pdf
To ensure print quality and to avoid damage to the printer, the printer stops operating after the photoconductor kit has reached approximately 60,000 pages (Letter/A4). The message 84 Replace PC Unit is displayed when the printer reaches this point. If the Toner Alarm setting is set to Single or Continuous (default is Off), the printer automatically notifies you before the photoconductor reaches this point and displays the message 84 PC Unit Life Warning. To avoid having the printer stop operating, replace the photoconductor kit when you first receive the 84 PC Unit Life Warning message. Once the photoconductor kit has been replaced, normal printer operation resumes

You need to replace. It is also called the drum unit.

http://www.nextag.com/dell-1720-photoconductor/shop-html

If I could be of further assistance, let me know. If this helps or solves the issue, please rate it and give a testimonial for my response

Thanks, Joe

I’m happy to assist further over the phone at https://www.6ya.com/expert/joe_8b8c2cd6ce148309

The photoconductor kit is another word for the drum or imaging drum. All three words refer to the same part.

Here is a link from the Dell site for this model.
http://accessories.us.dell.com/sna/PopupProductDetail.aspx?c=us&l=en&cs=dhs&sku=310-5404

Once you replace the drum, the printer has to be manually reset. If this is not done, the printer will continue to give this print out. By resetting it, the counter is set back to zero. The drum is good for around 30k prints.

From the Online Manual for the 1700, to reset the counter:
http://support.dell.com/support/edocs/systems/1700n/en/index.htm#online_documentation

To reset the counter, press and hold the Cancel button until all lights flash in sequence.

NOTICE: Resetting the imaging drum's counter without replacing the imaging drum may damage your printer and void your warranty.

After you replace the imaging drum, you should reset the imaging drum's counter. To reset the counter, press and hold the Cancel button until all lights flash in sequence.

http://support.dell.com/support/edocs/systems/prn1720/en/1720_en/en/d0e4183.html#replacing-the-imaging-drum

you must reset the error message; find the explanation in the photoconductor kit package

I believe this message is occur because the laser printer drum needs to be replaced, not the toner cartridge.

These are two different things. The part is a DELL 310-8710 Drum Unit. Just google DELL 1720N drum and you should be able to find one.

After replacing fysicalythe photoconductor/imagaging drum, leave the door open. Press and hold Cancel untl all lights flash in sequence to reset the printer. Close front cover.

The second link was the helpful information. Also, to cut through all of that --

If you need to reset the counter:

1. Remove drum kit with toner

2. Make sure all print jobs are flushed otherwise whatever has been sent and not printed will come spewing out.

3. Hold down CANCEL Button until all lights flash through.

4. Slide the drum kit and toner properly into the Printer.

done.

Here is how to reset the photoconductor kit counter:

1. Make sure the new kit is installed and the printer is turned ON.

2. Open the front panel.

3. Hold the Cancel button in until the front panel LEDs flash.

4. Close the front panel