Canon np 6545 blank copies

[blazebusiness]

Old copier with a lot of clicks has blank copies. Once in a while but very infrequently when you power off the copier and turn it back on you may get 1 copy. And then reverts to blank copies again. One of my techs has Swapped out the following from a working model- coronas....potential control assy....lamp regulator pcb....entire drum unit....varistor.....dc controller......dv unit.....hvt.....pot control pcb assy etc...

I,m about to take over the call and go there myself. Any ideas much appreciated. For starters im thinking xfer corona connecter grounding out or something of that nature.

[Rachid.Akli]

In these models (analog copiers with potential control) when the scanning lamp doesn't light, you will get a blank copy because the DC bias will be at its maximum value and toner will not be able to go to the drum (no developement).By the way, what are the values of Vdm and VLm in display mode.Rachid.

[blazebusiness]

In these models (analog copiers with potential control) when the scanning lamp doesn't light, you will get a blank copy because the DC bias will be at its maximum value and toner will not be able to go to the drum (no developement).By the way, what are the values of Vdm and VLm in display mode.Rachid.

Thanks for replying - Scan lamp has already been replaced by my tech and lights up fine. I inspected the reflector to make sure it was ok after his work on the scan lamp. Vdm - 453v , VL1M - 173v , VL2M - 153v. I'm thinking maybe the connector in the back of the machine behind the xfer corona or the high voltage cables from the hvt or wiring. Some times if you manually darken the copies a super faint image appears to be visible but most the time not even darkening it will make an image. Sometimes after power is cycled you may get 1 copy before blank copies start but most of the time even cycling power has no effect.

[Rachid.Akli]

Try to replace the developing cylinder cluch CL8. and verify its rotation.

The pretranster corona (if not replaced) can create a short-circuit and results in zero transfert current.

Rachid

[blazebusiness]

Try to replace the developing cylinder cluch CL8. and verify its rotation.

The pretranster corona (if not replaced) can create a short-circuit and results in zero transfert current.

Rachid

Sounds like you and i think just alike. Already tried all that and ran copier without the prexfer corona. Next i,m gonna check the ms5 microswitch. I seem to remember that can cause this as well.

[Herrmann]

did you try to disable the potential control via service mode? does the image change? open the door while making sky copies, how do the drum surface look like?

[oldschool]

I remember working on a NP Canon that had a problem like this. Memory is fuzzy but I seem to remember this copier had a corona socket that had a hairline crack in it. Caused HVT output to be grounded out and shut down.
Another odd thing I remember causing blank copies with Canons.
HVT did not have a good ground.

[blazebusiness]

did you try to disable the potential control via service mode? does the image change? open the door while making sky copies, how do the drum surface look like?

Yes disabled potential control in service mode with no change in problem. So that makes me want to look at the connector that the xfer corona plugs into (what oldschool calls socket) or hv cables or the microswitch. Will let you guys know what fixes it and thanks very much for all the replies.

[irtek]

I would be looking more towards the Primary charge instead of transfer. Most of the time on Canons even if you lost transfer you would get a faint image from the paper hitting the drum. Most of the time if it was totally blank it would be Primary charge missing. Another thing to check is the drum drive. Had an NP8530 that a set screw came loose on the drum drive gear and had blank copies.