BH C284E CQ: Uneven density, "fuzzy" black @ max density

[907tec]

Have a C284e with only 100k giving me problems. Main issue is that the density is uneven from front to back. See attached scans. Light density patterns (30) for Cyan and Magenta attached, showing that front and rear of machine are lighter than the middle. Issue occurs with all colors, but more obvious on cyan/magenta. Second issue, likely related, is that test patterns containing maximum density K patches show "fuzz". See the attached printer demo page. D-Max boxes have a sort of "halo" around them, almost as though drum's charge is leaking out.

None of the consumables are over-life.

Have already tried:
Drums (New K drum still installed, tested with CMY drums from known-working machine)
Dev Units (CMYK dev units tested from known-working machine)
Transfer Belt (still has the new one installed)
2nd Transfer (still has the new one installed)
Cleaned laser windows (repeatedly)
Cleaned IDC sensors and checked cover actuation
HV Unit (and checked contacts/springs for signs of damage/arcing)
PRCB Unit (sounds weird, but suggested by service manual)
Frimwar

After each part was installed, I ran gradation adjusts and eventually init+stab's. Level History / Tables does not show abnormally high VDC/VG values for any color. IDC/ATDC/ATVC values all look normal.


Waiting for a repaired MFPB from Hytec right now, thinking about swapping PH from another machine in the meantime.

Anyone ever experience something like this?

SKMBT_C45117100515090.pdfSKMBT_C45117100515091.pdf

[blackcat4866]

Re: BH C284E CQ: Uneven density, "fuzzy" black @ max density

I've seen a couple bad lasers lately, and the affect is similar. I'd go with the laser ... excuse me: printhead unit. =^..^=

[907tec]

Re: BH C284E CQ: Uneven density, "fuzzy" black @ max density

Thanks, Blackcat. Somehow, I haven't had any laser issues on the later machines. Don't think I've swapped lasers on anything newer than c451s and c253s.

I'll try swapping the laser tomorrow. Will post results.

[korthr5]

Re: BH C284E CQ: Uneven density, "fuzzy" black @ max density

hello

Before you change the printhead, clean the flat cable on printhead, and on the adapter.

I have some color issues and clean the flat cables solve the problem.

[907tec]

Re: BH C284E CQ: Uneven density, "fuzzy" black @ max density

Thanks, Korthr5. I'll give that a shot before doing the full PH swap.

[REGSIS]

Re: BH C284E CQ: Uneven density, "fuzzy" black @ max density

Be careful: there are 2 versions of PH unit 1-beam and 2 beam. Also PH control board is different.

2-beam version has 2 flat cables of the same width, 1 beam version has 1wider flat cable, and 2nd is at half the width of the 1st one.

I had this fuzzy black issue long ago but that was black developing unit (a very visible defect - too much of toner brush at one point of magnet roller).

If your problem lies in PH unit (and you cover all the other possibilities) then you should try to clean the poligonal mirror which is the common part for all colours.
Also try to clean mirrors for black (fuzzy effect).
If the machine is working in smoking area 100 k is enough for "light steam" (don't know how percisely to describe the effect any other way) get caught on the edges of each side of poligonal mirror and that area doesn't reflect laser beam at full intensity.

[907tec]

Re: BH C284E CQ: Uneven density, "fuzzy" black @ max density

Finally received a new printhead and LD board from KM under the "3 year" program. Appears to have fixed the copy quality problem. Never seen a printhead have this particular effect, but it is apparently the culprit.

[907tec]

Re: BH C284E CQ: Uneven density, "fuzzy" black @ max density

Thanks for the tip, Regsis. I only had a 2-beam PH on hand, so had to order a single beam anyways. I haven't cracked open any of the newer printheads yet, glad that this one was covered under warranty so I didn't have to try it here. Will definitely keep your suggestion in mind, just in case I encounter it out-of-warranty.