I have a new Ricoh C820DN printer. Did about 12k prints fine and now doesn't seem to print Cyan toner on the bottom half of page (all colors work fine at top of page but at the bottom, anything that uses Cyan doesn't seems to drop the cyan color). I've changed all toners and PCU, fuser, transfer units all seem fine. Any suggestions? Thanks

You just have a problem with colour PCU (SC 365 - magenta, SC366 - cyan). The main reason is that toner density is abnormal. Sometimes, when you replace toners, printer receive to much toner for a short time, and after that you have an abnormal toner density (higher). You can check in service mode (hold up and down arrows for 6-7 sec, release them and press ok button) following thing :
choose 2. engine
then with arrows choose 3. process
then choose Vt display,
for each color by default there should by somewhere arround 2.4V. If you see for some colors, for example 0.02V, then this is a problem(to much toner). In this case the only thing that you can do is to restart printer and try to print enough pages, filled with problem color. Usually you can print max 3 pages. Then restart printer and try another 3 pages. Print until the you will be able to print at least 4 pages continuously.
Good luck and remember that this is a technical problem and you should ask someone qualified for the job. I am sure that 80% of service engineers can't repair this issue. But I can.

could be black developer unit or pcu / try printing something from doc feeder or platen glass in each single color and see if you have same problem. If other color prints find then will narrow down to items above

I THINK THE CLEANING BLADE PROBLEM, IT TORN & CAUSED THE HORIZONTAL LINE EFFECT IN THE CYAN UNIT

check your printer preference setting in computer driver you will see default set to black and white. select doc then select printer goto printer preference and select color

Did you do a factory reset?

If your printer is missing a color it could be caused by (off the top of my head) 3 possibilities.
1. High voltage board
2. laser/scanner assembly for that color
3. DC controller might need a firmware upgrade, www.hp.com
Run the PQ diagnostics, check the cyan color
Run the Cartridge Disable diagnostic. Remove all cartridges and take the black cartridge and insert it where the cyan normally is. If the black prints in the cyan slot, your cyan cartridges are bad. If the black doesn't work then go to #3 above. It won't cost any money to upgrade the firmware. If it still doesn't work call in a printer tech.
At this point you may need a printer tech.

please DO NOT use PCL printer drivers. USE RPSC or PS (post script) drivers and everything will be OK
pifonski

If I remember right, the CL1000 won't print if any of the 4 colors are out. You have to replace the cyan toner in order to print, even in black and white.

If you haven't tried already, you can try taking the cyan toner out and shaking it up (just a little bit) to try to get the printer to find the little bit of toner left in the bottle.

replace the cyan image unit might go a bad one

Btw, I’m available to help over the phone in case u need at https://www.6ya.com/expert/normanj_7893313f0751935f

What ever color the line is you need to replace that photoconductor unit. They can be ordered from a Ricoh dealer and come with instructions for installing.