C451 white blotches in black background

[WaveyDavey]

Has anyone seen the problem on these machines? normal text is fine but if you run a skyshot or test mode half tone print you can see white blotches all over.
KM tech just say replace black unit and this does cure it but these are occuring quite often and at around 100k so looking for a solution.

thanks
see this image for an idea of the problem
http://www.thewilkesfamily.co.uk/images/blotches.tif

[ni311]

I didn't get it. Did you replaced the black IU and the problem remains or are you trying to find a solution before replacing the imaging unit?

[WaveyDavey]

if you change the unit it goes away. but this is happening on so many machines we need to find a resolution rather than keep changing units as they should last 300k not 100k

[Albonline]

the problem usually has to do with humidity in the enviorment.or lack there of. try reducing the background voltage and transfer voltages and increasing dmax value and tcr values. saw this problem alot in the 8020/8031 line. there is also a bias choise setting but you will loose the gradation adjustmet.

[Badhabit]

Hi there.

There seems to have been a bad batch of toner shipped out. We have been told to replace the toners with new ones and that has sorted out the problem as soon as the old toner has been worked out of the dev tank.

If you detect this early enough it doesn't take long for the blotches to dissapear.

Hope this helps.

[WaveyDavey]

interesting, thanks for the reply
do you have any batch numbers that KM are suggesting are a problem?

[Badhabit]

Will try and find out and let you know.