Shadow print image on Laerjet 6P

[The Natural Philosopher]

My trusty old 6p has developed a fault..

There is an exact duplicate image approx 1.2mm to the RIGHT of the main
image. Its less dense, but getting stronger every day..

I checked by faulting a page before it got to the toner assy, and the
duplicate image was there at that stage.

I cleaned the toner drum, and the mirror with the brush, but its no
better, in fact its steadily getting worse.

Always has used genuine HP parts..this toner is maybe 30% used -
installed earlier this year.


Any ideas? I am reluctant replace the toner/drum assembly, cos i can't
see how it can be the problem. Looks to me like a split mirror, or dirt
in the optics.. but I am fairly clueless as to what actually does what..

Its also a bit faint overall down the left hand side..

 

[Tony]

My trusty old 6p has developed a fault..

There is an exact duplicate image approx 1.2mm to the RIGHT of the main
image. Its less dense, but getting stronger every day..

I checked by faulting a page before it got to the toner assy, and the
duplicate image was there at that stage.

I cleaned the toner drum, and the mirror with the brush, but its no
better, in fact its steadily getting worse.

Always has used genuine HP parts..this toner is maybe 30% used -
installed earlier this year.


Any ideas? I am reluctant replace the toner/drum assembly, cos i can't
see how it can be the problem. Looks to me like a split mirror, or dirt
in the optics.. but I am fairly clueless as to what actually does what..

Its also a bit faint overall down the left hand side..

You say the ghost is to the right. Is this when you hold the paper long side
horizontally (landscape) and are you using A4 or Letter size paper? This is
important to diagnose the issue.
The printer cannot insert a ghost before the paper reaches the toner cartridge,
are you saying that the ghost image appears on the paper before the fuser (at
the back of the printer)?
Tony
MS MVP Printing/Imaging

 

[The Natural Philosopher]

You say the ghost is to the right. Is this when you hold the paper long side
horizontally (landscape) and are you using A4 or Letter size paper? This is
important to diagnose the issue.

Actually I meant to the right of the direction of feed. A4 portrait,
narrow end fed into machine. Image to the roight.

The printer cannot insert a ghost before the paper reaches the toner cartridge,
are you saying that the ghost image appears on the paper before the fuser (at
the back of the printer)?

Sorry. Meant fuser.
Double image came right off toner assy. Its like there were two
lasers..one a bit to the right..
Cant be stiff sticking to drum, cos that would give a 'later' image down
the page. Must be making two images..

does the laser move across the drum or is it done with mirrors?

 

[Tony]

Actually I meant to the right of the direction of feed. A4 portrait,
narrow end fed into machine. Image to the roight.



Sorry. Meant fuser.
Double image came right off toner assy. Its like there were two
lasers..one a bit to the right..
Cant be stiff sticking to drum, cos that would give a 'later' image down
the page. Must be making two images..

does the laser move across the drum or is it done with mirrors?

It really does look like the drum has failed. This can happen, how old is the
cartridge?
If you do the test you described (stopping the print) and the ghost is on the
paper before the paper has been through the fuser then this is a drum failure.
The lasewr travels across the drum by virtue of a set of rotating mirrors.
Tony
MS MVP Printing/Imaging

 

[The Natural Philosopher]

It really does look like the drum has failed. This can happen, how old is the
cartridge?

Well I had it about 2 years before I needed it..so its about 3 years old
total

If you do the test you described (stopping the print) and the ghost is on the
paper before the paper has been through the fuser then this is a drum failure.

I did and it happens at that stage, yes..

The lasewr travels across the drum by virtue of a set of rotating mirrors.
Tony

Then suppose one mirror is cracked or broken or dirty..sending a double
image..is that mirror in the cartridge assembly?

Or is it somewhere else..

I can see how a faulty drum might give a weak image, but I can't see how
it can make two images..


Bear with me here..there is a long flat mirror that you clean with a
brush..Am I to understand the beam is bounced off that onto the drum? by
another rotating mirror in the guts of the beast somewhere? Then that
sets up a charge that sucks the toner up and thats how it gets to the
paper..

What concerns me is what if its not the drum? I get a new one and then
have to throw the printer away anyway...servicing a 15 year old machine
is hardly worth it I would think.

 

[jasee]

I can see how a faulty drum might give a weak image, but I can't see
how it can make two images..


Bear with me here..there is a long flat mirror that you clean with a
brush..Am I to understand the beam is bounced off that onto the drum?
by another rotating mirror in the guts of the beast somewhere?

Yes, there are in fact a few mirrors and usually a prism. Personally I think
it's more likely that 'something' has become detatched inside the laser unit
and is causing another reflection of the image.

What concerns me is what if its not the drum? I get a new one and then
have to throw the printer away anyway...servicing a 15 year old
machine is hardly worth it I would think.

Probably not.

 

[Tony]

Well I had it about 2 years before I needed it..so its about 3 years old
total



I did and it happens at that stage, yes..


Then suppose one mirror is cracked or broken or dirty..sending a double
image..is that mirror in the cartridge assembly?

Or is it somewhere else..

I can see how a faulty drum might give a weak image, but I can't see how
it can make two images..


Bear with me here..there is a long flat mirror that you clean with a
brush..Am I to understand the beam is bounced off that onto the drum? by
another rotating mirror in the guts of the beast somewhere? Then that
sets up a charge that sucks the toner up and thats how it gets to the
paper..

What concerns me is what if its not the drum? I get a new one and then
have to throw the printer away anyway...servicing a 15 year old machine
is hardly worth it I would think.

The "mirror" you refer to is actually a lens. The laser scanner us behind that
lens. There are mirrors in the laser scanner area that are accurately made to
direct the laser beam to the correct part of the drum at the correct time.
I have never seen a laser fail in the way you describe.
Drum units do produce ghosts very, very often. In fact I would say that it
happens in about 10% of all drums that are at end of life.
There is a way to be absolutely sure before you spend any money.
Measure the distance between the "beginning" of the real image and the
"beginning" of the ghost image, measure it accurately and do so using an easily
identifiable part of the image and post that here. I will advise exactly what
is causing the problem. You mentiioned 1.2mm to the right, that distance has no
particular relevance in my experience. You need to place the paper in Portrait
mode (assuming A4 or Letter or similar paper) and measure vertically.
Then you can decide whether to spend the money or not.

Tony
MS MVP Printing/Imaging

 

[The Natural Philosopher]

Measure the distance between the "beginning" of the real image and the
"beginning" of the ghost image, measure it accurately and do so using an easily
identifiable part of the image and post that here. I will advise exactly what
is causing the problem. You mentiioned 1.2mm to the right, that distance has no
particular relevance in my experience. You need to place the paper in Portrait
mode (assuming A4 or Letter or similar paper) and measure vertically.
Then you can decide whether to spend the money or not.

The image is displaced *only* to the right. There is no vertical
displacement (in the direction of drum rotation) at all.

The displacement is about 1.2mm, *consistent all across the paper width*.

I am sorry it's not relevant to your experience, but it remains a fact ;-)

If it were simple 'one drum rotation' ghost I would have been able to
solve it using google..

The problem is steadily getting worse.

There is also a lessening of print density at the left hand side of the
paper..but that make simply be the toner cartridge getting empty.

The printer hasn't been radically moved or subject to any shocks..which
is why I am at a loss to understand why this problem has developed.

 

[The Natural Philosopher]

Yes, there are in fact a few mirrors and usually a prism. Personally I think
it's more likely that 'something' has become detatched inside the laser unit
and is causing another reflection of the image.

Thats my take at this point..but what? Do I risk £55 on a new drum? Or
simply get a new printer..this one is full to the gills with RAM and a
postscript cartridge, and would be fairly costly to replace...to a
similar spec, even if a modern one supported win98 drivers And MAC
OS9 drivers..etc.

 

[jasee]

Thats my take at this point..but what?

Don't know, you'd have to take it apart to see.

Do I risk £55 on a new drum? Or
simply get a new printer..this one is full to the gills with RAM and a
postscript cartridge, and would be fairly costly to replace...to a
similar spec, even if a modern one supported win98 drivers And MAC
OS9 drivers..etc.

If second image was displaced vertically then it might (possibly) be the
drum or several other things but I can't see it, as it's only displaced to
the right.

For under a hundred pounds you could get my favourite printer on Ebay (in
the uk). (It seems you're from the uk). Thats the hp 1320n (with drivers for
W98 and MAC 0s9 upwards). It's quiicker than the 6p, more ecofriendly,
ultimately probably less robust, but easier to maintain in a least one
respect. Ram (you probably don't require it) is available very cheaply for
this printer about £35 for 128megs IIRC.

 

[Tony]

The image is displaced *only* to the right. There is no vertical
displacement (in the direction of drum rotation) at all.

The displacement is about 1.2mm, *consistent all across the paper width*.

I am sorry it's not relevant to your experience, but it remains a fact ;-)

If it were simple 'one drum rotation' ghost I would have been able to
solve it using google..

The problem is steadily getting worse.

There is also a lessening of print density at the left hand side of the
paper..but that make simply be the toner cartridge getting empty.

The printer hasn't been radically moved or subject to any shocks..which
is why I am at a loss to understand why this problem has developed.

I missed an important part of one of your earlier posts.
I think that your printer has probably developed an electronic fault in the
engine controller assembly. I have never seen this symptom but I cannot see how
a lateral ghost can be mechanical.
I suspect printer replacement is the best thing for you.
Sorry I could not be of better help.
Tony
MS MVP Printing/Imaging

 

[The Natural Philosopher]

I missed an important part of one of your earlier posts.
I think that your printer has probably developed an electronic fault in the
engine controller assembly. I have never seen this symptom but I cannot see how
a lateral ghost can be mechanical.
I suspect printer replacement is the best thing for you.
Sorry I could not be of better help.

Well a bit of dirt on a lens or mirror could make a double image all right.

However it may be that a new printer is on the santa list..

 

[Tony]

Well a bit of dirt on a lens or mirror could make a double image all right.

Yes it could, but not right across the page.
Tony

However it may be that a new printer is on the santa list..

Tony
MS MVP Printing/Imaging

 

[jasee]

Yes it could, but not right across the page.

Why not? If it's present before the beam hits the revolving mirror/prism
then that's exactly the effect it might have.

 

[Tony]

Why not? If it's present before the beam hits the revolving mirror/prism
then that's exactly the effect it might have.

Think about the way the laser scanner works.
A laser beam shines onto a rotating polygon of mirrors, these mirrors direct
the beam through a lens that is shaped to ensure that the resulting charge on
the drum is linear. On it's way to the drum the beam usually passes through a
window, the purpose of which is to prevent dust from entering the scanner
chamber but which has no other impact on the resulting image. Assuming a
printer has 600x600 dpi resolution, the scanner will lay down 600 separate
charges on the drum and then the drum will rotate 1/600 of an inch and another
600 charges will be laid down. The number of rotations of the mirrors per drum
movement may well be different with different printers. In practice of course
the drum is moving at a uniform speed and does not actually stop and start
every 1/600 of an inch.
If there is dirt or a crack or any other damage to any part of the optics there
will be one, and only one, occurence of the resulting defect for each mirror
rotation and the width of that defect will be proportional to (but not
necessarily equal to) the width of the piece of dirt or damage. Therefore the
defect will not occur across the entire page.
If there is something that affects the beam before it hits the rotating mirrors
it will simply affect the charge differential on the drum.
The image defect that the OP has experienced sounds like "smearing" to me.
Smearing is nearly always caused by one of three things.
1. Incompatible paper - it is most unlikely that this would result in a uniform
horizontal ghost.
2. Toner deposits on the fuser rollers - not the case because the defect is
present before the paper reaches the fuser.
3. DC Controller failure (in some HP printers this is the Engine Control
Assembly) - if in doubt read the HP manuals.
Hence my advice.
Tony
MS MVP Printing/Imaging

 

[jasee]

Think about the way the laser scanner works.
A laser beam shines onto a rotating polygon of mirrors, these mirrors
direct the beam through a lens that is shaped to ensure that the
resulting charge on the drum is linear. On it's way to the drum the
beam usually passes through a window, the purpose of which is to
prevent dust from entering the scanner chamber but which has no other
impact on the resulting image. Assuming a printer has 600x600 dpi
resolution, the scanner will lay down 600 separate charges on the
drum and then the drum will rotate 1/600 of an inch and another 600
charges will be laid down. The number of rotations of the mirrors per
drum movement may well be different with different printers. In
practice of course the drum is moving at a uniform speed and does not
actually stop and start every 1/600 of an inch.
If there is dirt or a crack or any other damage to any part of the
optics there will be one, and only one, occurence of the resulting
defect for each mirror rotation and the width of that defect will be
proportional to (but not necessarily equal to) the width of the piece
of dirt or damage. Therefore the defect will not occur across the
entire page.

Obviously, if the defect is present after the laser has gone through the
mirror/prism. I think in fact the dirt or damage could be quite difficult to
detect, depending on where it was situated and its size (obviously) as the
beam fans out from the mirror/prism arrangement as it passes through
subsequent mirrors and the defect would show up as an absence of print
(which could be quite small) travelling down the paper vertically.

If there is something that affects the beam before it hits the
rotating mirrors it will simply affect the charge differential on the
drum.

Do you mean it will reduce the charge differential on the drum? There will
simply be a grey(er) image?
I'm suggesting that there will be two beams.

The image defect that the OP has experienced sounds like "smearing"
to me. Smearing is nearly always caused by one of three things.
1. Incompatible paper - it is most unlikely that this would result in
a uniform horizontal ghost.
2. Toner deposits on the fuser rollers - not the case because the
defect is present before the paper reaches the fuser.
3. DC Controller failure (in some HP printers this is the Engine
Control Assembly) - if in doubt read the HP manuals.

Quite good explanation.
However, I've got quite a few Hp service manuals and I think that an
electrical fault associated with the laser is a distinct possibility. I know
how the scanning process works, it's fairly simple in principle. More
importantly, I've opened a laser unit and I've seen how a laser unit works
in practice. The laser (in the unit I looked at) was focused using a lense
before it was directed at the rotating mirror arrangement. It is here that a
small (very small!) object could conceivably divert part of the beam, I
suppose a cracked lens could also do this, but it seems unlikely. In
practice, the laser's path can be quite convoluted and can pass through
quite a number of mirrors if the laser unit is compact as it's got to fan
out from a single point to, eventually, the width of a piece of paper.

 

[The Natural Philosopher]

Think about the way the laser scanner works.
A laser beam shines onto a rotating polygon of mirrors, these mirrors direct
the beam through a lens that is shaped to ensure that the resulting charge on
the drum is linear. On it's way to the drum the beam usually passes through a
window, the purpose of which is to prevent dust from entering the scanner
chamber but which has no other impact on the resulting image. Assuming a
printer has 600x600 dpi resolution, the scanner will lay down 600 separate
charges on the drum and then the drum will rotate 1/600 of an inch and another
600 charges will be laid down. The number of rotations of the mirrors per drum
movement may well be different with different printers. In practice of course
the drum is moving at a uniform speed and does not actually stop and start
every 1/600 of an inch.
If there is dirt or a crack or any other damage to any part of the optics there
will be one, and only one, occurence of the resulting defect for each mirror
rotation and the width of that defect will be proportional to (but not
necessarily equal to) the width of the piece of dirt or damage. Therefore the
defect will not occur across the entire page.
If there is something that affects the beam before it hits the rotating mirrors
it will simply affect the charge differential on the drum.
The image defect that the OP has experienced sounds like "smearing" to me.
Smearing is nearly always caused by one of three things.
1. Incompatible paper - it is most unlikely that this would result in a uniform
horizontal ghost.
2. Toner deposits on the fuser rollers - not the case because the defect is
present before the paper reaches the fuser.
3. DC Controller failure (in some HP printers this is the Engine Control
Assembly) - if in doubt read the HP manuals.
Hence my advice.

Thanks for finally explaining enough about this for me to get a handle
on it.

The situation has deteriorated to the point where I now have two equal
weight images..at half density and only full density where they overlap.

Text has become illegible, urgency has crept in, and the choice between
expensive repairs and a new printer is biased in the latter direction.

For future reference and the record, a search of HP's databases revealed
that my fault is rare, but not unique. Several occurrences of 'double
images' displaced by a mm or so were to be found..and no resolution of
the problem was ever noted in the threads.

In fact most of them ended in either dead silence and no response, in
the usual 'change your drum' followed by 'doesn't work' or in a handful
of cases some mutterings about 'change this/that circuit board or
possibly the laser assembly'

Now when this printer was new, around 1986, it got struck by lightning -
you don't believe me? well my overhead hone line took a direct strike,
the modem was fried, the serial parallel card in the 8086 'IBM Clone'
computer was fried, half the electronics in the house died and I had
blown out wall plates everywhere..and I called in HP techs to fix the
printer. It was under warranty still.

Tow circuit boards - the I/O and the PUS were gone, and he tried to
charge me about $1000 to fix what was then a $900 printer..I suggested
that he should pack his bags and leave ..as that was more than a new one
would cost..he said he only had two boxes to tick 'free under warranty'
or 'full price due to it being a fault not of HP's manufacture or design'

I said that was his choice..and he ticked the 'free under warranty'
box...

I mention all this for the record. so others searching with this fault
won't waste their time trying to fix a printer at a likely cost of more
than its worth. Which is sad. I have already put a new power supply and
drive belt in my HP DesignJet 650C...Id be happy to re-board this one
too..if I knew how to get it apart and which board to replace, and could
get the board at the right price.

 

[The Natural Philosopher]

Obviously, if the defect is present after the laser has gone through the
mirror/prism. I think in fact the dirt or damage could be quite difficult to
detect, depending on where it was situated and its size (obviously) as the
beam fans out from the mirror/prism arrangement as it passes through
subsequent mirrors and the defect would show up as an absence of print
(which could be quite small) travelling down the paper vertically.


Do you mean it will reduce the charge differential on the drum? There will
simply be a grey(er) image?
I'm suggesting that there will be two beams.


Quite good explanation.
However, I've got quite a few Hp service manuals and I think that an
electrical fault associated with the laser is a distinct possibility. I know
how the scanning process works, it's fairly simple in principle. More
importantly, I've opened a laser unit and I've seen how a laser unit works
in practice. The laser (in the unit I looked at) was focused using a lense
before it was directed at the rotating mirror arrangement. It is here that a
small (very small!) object could conceivably divert part of the beam, I
suppose a cracked lens could also do this, but it seems unlikely. In
practice, the laser's path can be quite convoluted and can pass through
quite a number of mirrors if the laser unit is compact as it's got to fan
out from a single point to, eventually, the width of a piece of paper.

Yes.. that was my final take..a speck of dirt in or near the laser
itself..or some electronic fault.

Anyone know where the laser lives in a 6P or how to get at it?
I have a strong feeling that a lens brush with a bellows on it - which I
have - would probably fix this..

 

[Tony]

Thanks for finally explaining enough about this for me to get a handle
on it.

The situation has deteriorated to the point where I now have two equal
weight images..at half density and only full density where they overlap.

Text has become illegible, urgency has crept in, and the choice between
expensive repairs and a new printer is biased in the latter direction.

For future reference and the record, a search of HP's databases revealed
that my fault is rare, but not unique. Several occurrences of 'double
images' displaced by a mm or so were to be found..and no resolution of
the problem was ever noted in the threads.

In fact most of them ended in either dead silence and no response, in
the usual 'change your drum' followed by 'doesn't work' or in a handful
of cases some mutterings about 'change this/that circuit board or
possibly the laser assembly'

Now when this printer was new, around 1986, it got struck by lightning -
you don't believe me? well my overhead hone line took a direct strike,
the modem was fried, the serial parallel card in the 8086 'IBM Clone'
computer was fried, half the electronics in the house died and I had
blown out wall plates everywhere..and I called in HP techs to fix the
printer. It was under warranty still.

Tow circuit boards - the I/O and the PUS were gone, and he tried to
charge me about $1000 to fix what was then a $900 printer..I suggested
that he should pack his bags and leave ..as that was more than a new one
would cost..he said he only had two boxes to tick 'free under warranty'
or 'full price due to it being a fault not of HP's manufacture or design'

I said that was his choice..and he ticked the 'free under warranty'
box...

I mention all this for the record. so others searching with this fault
won't waste their time trying to fix a printer at a likely cost of more
than its worth. Which is sad. I have already put a new power supply and
drive belt in my HP DesignJet 650C...Id be happy to re-board this one
too..if I knew how to get it apart and which board to replace, and could
get the board at the right price.

The hardest part is (believe it or not) removing the cover, when you have the
top cover off the laser sits immediately below the cover.
Go to http://www.eserviceinfo.com/equipment_mfg/HP_22.html and download the 6
parts of the Laserjet 4L manual, then go to
http://www.eserviceinfo.com/downloa.../6mp (C3150A / C3155A / C3980A / C3982A).html
and download the 6P manual addendum. They will provide instructions on removal
of various parts but will not explain how to take the laser assembly apart (HP
does not provide this information because they only provide complete laser
assemblies, not the parts inside). The laser is easy to take apart however and
will become obvious when you see it. Be very careful with the mirrors and lens.
The 6P was based on the 4L and 4P printers, hence the need to download the 4L
manual.
I sincerely hope that you are able to fix this but I am doubtful, I do not
believe this is a speck of dirt or similar. Dirt will not cause this if it is
on the mirrors or lens (as explained elsewhere in this thread).
Nevertheless good luck. The one ray of hope is the new information you have
provided that "I now have two equal
weight images..at half density and only full density where they overlap" but I
suspect this is not caused by a "split beam" but by an electronic failure in
the DC controller which is a very expensive part unless you can get it from
another 6P that has a different problem.
Tony
MS MVP Printing/Imaging

 

[The Natural Philosopher]

The hardest part is (believe it or not) removing the cover, when you have the
top cover off the laser sits immediately below the cover.
Go to http://www.eserviceinfo.com/equipment_mfg/HP_22.html and download the 6
parts of the Laserjet 4L manual, then go to
http://www.eserviceinfo.com/downloa.../6mp (C3150A / C3155A / C3980A / C3982A).html
and download the 6P manual addendum. They will provide instructions on removal
of various parts but will not explain how to take the laser assembly apart (HP
does not provide this information because they only provide complete laser
assemblies, not the parts inside). The laser is easy to take apart however and
will become obvious when you see it. Be very careful with the mirrors and lens.
The 6P was based on the 4L and 4P printers, hence the need to download the 4L
manual.
I sincerely hope that you are able to fix this but I am doubtful, I do not
believe this is a speck of dirt or similar. Dirt will not cause this if it is
on the mirrors or lens (as explained elsewhere in this thread).
Nevertheless good luck. The one ray of hope is the new information you have
provided that "I now have two equal
weight images..at half density and only full density where they overlap" but I
suspect this is not caused by a "split beam" but by an electronic failure in
the DC controller which is a very expensive part unless you can get it from
another 6P that has a different problem.
Tony
MS MVP Printing/Imaging

You are a star mate..

I am pretty much at the point of driving off to get a new printer..but
this might just be worth a go..

HOW DO I UNCOMPRESS TEH .RAR FILES.. and what do print them on..haha!