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.

[don]

Dear Sir,

I request you to check with PWB-MC once.
Regards..

[mrwho]

Thank you all for your kind feedback, but since I've managed to break this machine's PSU into pieces I can't do anything else until we get another power supply.

FML!

[mrwho]

Hello, guys and girls! Remember this thread?

Okay, first of all, the trouble was caused by an HV contact which, due to rust, broke into pieces (image B). I'm talking about those thin wires coiled at the end that make contact between the IUs and the HV board.

My trouble is that I managed to take out the black IU contacts, but I'm unable to do so with the remaining assemblies (image A) - the manual says nothing about it and I never done it before.

Anyone who got this PITA assignment can tell me how can I do it?