Can't print yellow on konica c450 bizhub

[chriscctx]

Having trouble getting the konica minolta c450 to print yellow. Transfer belt is not even at half life. Have changed the yellow imaging unit three times now with no difference. I can however take the yellow imaging units and put them in a different machine and they work just fine. So I guess I can rule out the IU. Have also cleaned the inside - still with no effect. What am i missing?

Thanks

[DUKEY]

sounds like could be laser related! that machine has seperate lasers for each, did you try doing test prints?

[remati]

--in "tech mode"
you must print the test chart CMYK in gradaction part.You will have de 4 printed pages
this a good test for the laser

[Stirton.M]

sounds like could be laser related! that machine has seperate lasers for each, did you try doing test prints?

There are no laser units in a C450. They are all LED print heads.

Since the machine is not throwing a code, it is not an obvious issue. It is possible the ribbon cable to the board beneath the print head has slipped out.

The unfortunate thing here is troubleshooting the problem is time consuming. About 2 hours. Remove the image units, transfer belt. Disconnect the harness of the print head unit from the PRCB and MCB. The drum drive couplings inside the developer area, push those towards the back and twist slightly. They should lock. Close the image unit lock levers. Remove the two screws holding the unit in place (waste toner bottle side) and the two ground tab screws. The unit should then slide out easily. Do not force. If you meet resistance, likely the drive couplings I mentioned earlier are still in the way.

If you have a spare LED bed, use that instead. Else....

From this point, swap the yellow LED array with one of the other colours (not black, it is a different part number). You will need to remove the black plastic moldings and such to get at the ribbon connections on the board underneath. The ribbon cables are held in place with press lock connectors that need to be lifted up to release. Press them back down when locking the ribbon cable in after.

Reverse the above procedures for installation.

If the problem moves, the LED unit is defective. If the problem does not move, problem is likely the LED driver board underneath the assembly.

[DUKEY]

Sorry thats what i meant! Lol...i've done the job a couple of times and it was a pain in the butt between taking all the covers off and releasing them!

[remati]

[chriscctx]

I did a CMYK gradation test - which only confirms that it is not printing yellow correctly. There is a side note - I did a test page of just solid yellow and ran 20 copies. The first page was a weak yellow coverage but every copy after that kept getting whiter until the last page had just barely a hint of yellow to it. And the edges of the test pages - about not quite an eighth of an inch on two sides are printing yellow correctly.

[Stirton.M]

out of curiosity, is the LED print head dirty?

Clean it using the wand with some isopropyl alcohol or methanol. Be sure to be vigorous when doing so.

This could also be due to poor bias connection related to that IU. No matter how you crunch it, you need to get your hands dirty and run that screwdriver to narrow down the problem.

[fishleg]

You need to check if its a power or drum issue. Not tried this but I would try putting your yellow into a different colour and just swap the drum chips round i.e. put the yellow in cyan with a different chip do your half tone etc if the problem goes away then you know your drum is fine and it can only be a power issue. Obviously don't do this for too long but at least one copy wont hurt it and you'll narrow your problem down a lot. Problem you may have though if its a power issue is your IU has sucked up all the dev and dumped it so which case your drum is screwed anyway.

All the ones I have seen its always been the bottom power supply loses its dev bias which usually causes the dev to be lifted into the drum and hence your faint copies eventually.

[Brischaffer]

I had the same problem on a C353. Im not sure if there the same but what I found was behind the High Voltage Board. Take the board off and there are four plastic shafts with srings on the end of them. They kind of snap in. I found that the yellow one came loose and that was the problem. Once i snapped it back in the yellow came back to life. I will warn you that i had to take everything off to get to it. So plan on being there for awhile. Hope this helps.