C250 black background

[mrwho]

Hello there, guys and girls!

I'm about to take appart a C250 which is making some black backgrounds on every copy and print that comes out.

It seems like a Bias-related problem, since if I take out a color gradation pattern (attached), the background dissapears in the areas where it prints solid-black squares.

If anyone that already has solved this kind of trouble can give me some kind of shortcut so I can take this machine out of my repair shop, I'd be very grateful!

Cheers!

[kingarthur]

Have you tried partially covering the printhead. If the fault disappears where the head is covered, it's probably either the printhead itself or the MFP pcb

[mrwho]

Didn't ocur to me, but it's a great idea! Gonna put it into work right now! I'll give some feedback soon!
Thanks!

[mrwho]

Well, that was worth a try, but didn't make a difference. I partially blocked the black ph (using the printhead cleaner jig) and made another print - the background still fills up the entire sheet.
Also reflashed it, but still the same.
Going to disassemble the bugger to try and find out what's wrong!
Thanks anyway!

[copytechman]

Does it do it in monocolour mode? (Say Cyan) or Black mode? Just thoughts!

Regards!
A.

[mrwho]

That's a little hard to test right now, since the machine is in pieces all around the floor!

But as soon as I assemble it, I'll try monocolor to see what happens.

It happens in both CMYK and K copies and printouts, though.

[mrwho]

News update: When disabling BIAS, the background disappears.

I'm starting to suspect HV1 is busted. How often do these boards fail?

[mrwho]

Well, just tested HV1 on a different working machine. It didn't show any of the symptoms, so I'm quite sure the HV1 is OK.

So, if the HV1 isn't to blame and when I disconnect the BIAS on the IU the prints come out better, what could possibly be wrong?

I'm about to rip my hair over this...

[kingarthur]

maybe the contact at the back of the m/c isn't quite connecting properly with the IU

[copytechman]

That test shot looks like 11x17. Check the drum gnd contact @ the front of the iu(s)@ the top where it connects to the frame... make sure its solid! Had a c250 do something kinda like this and would do it worse in colour mode.. Reformed the contacts to make em more "aggressively" contact the frame... problem solved!

Regards!
A.