skew in 6501

[levino]

Hai all,

2 mm skew is apperaing on my KM 6501 from 4th and 5th tray ,
i followed installation procedure no chance,

please help
thanks in advance
levi

[lucky13]

what size and weight paper ?

[random]

Is the floor level?

[mgutski]

is the skew first side or second side?

[levino]

sorry for the delay
Customer is using only 13x19 paper and the weight from 170,216,250,285 gsm,the skew is in the front side.The floor is level and the pf was installed and checked with leveler.
thanks all

[dljorg]

Just dealt with one of these where tray 4 was OK but got this type skew from tray 5. PF unit appeared level but not quite. Sounds strange but we REALLY got it level. Attach pins would slide in and out with fingers and using a 3 foot construction level got the corners and crosswise level to exactly within the level bubble lines. Ended up with some blocks under the PF unit feet in one corner. Fixed this one - maybe yours too?

[sbillis]

I have a same problem.

Some times image is shifting or skewing on 13x19 heavy 300gsm stock Coated-MO.
Centering, Restart timing, FD and CD adjustments are made, but few days later same problem appears again.

- Centering sensos (PF and ADU) must be on or off?
- 3mm gap from PF does it matters?
- FD,CD,Centering,Restart Timin must be done with A3 paper(11x17) or 13x19 or anything else customers using and what wheight.
- Skew can be corrected from ADU mechanical adjustment or from CD Skew software adj?

thanks for reading

[HORSE]

Is that 2mm skew on first side or is it 2mm front/back? (1mm front/ 1mm back)

1mm per side is normal. really you might get it spot on but it will wander 0.75-1mm through out the run. Re-educate your customer.

Note: Specs for skew is 0.5% over the length, So for 320x450mm skew would be 2.25mm per side. (450x0.5%=2.25)

[Stirton.M]

see my attached document for information on how to set the PFU. Just because a level says it is level, does not mean it is even with the machine. Bubble levels, far too much variance in this analog method. A tiny bit of unlevel relative to the main body and the PFU can result in a skew.

Making sure the lock pins are nice and loose (easy to remove or insert) is only part of the equation.

The attached document illustrates the rest.

Also, not noted in the document is the entrance rollers of the ADU itself. There are two hard plastic rollers held against the rubber rollers below, kept relatively tight against them with springs over the shaft.

Sometimes, the user might get a jam where the paper is mostly in the ADU, but some of it is still in the exit of the PFU, not enough to grab onto and remove. The ADU is normally locked to prevent it from being pulled out in these cases. Unlocking it, the paper will be pulled to the rear of the ADU and eventually bunch up and tear. This presents two problems for us techs to fix.

One, removing any bits of paper stuck in the path of the horizontal section of the PFU, and the entrance to the machine mainbody. Second, bunched up paper in the entrance to the ADU will force the two plates apart, causing an imbalance of pressure on the ADU entrance rollers. This imbalance can result in skewing, especially in light stock or small paper formats. Large paper format can also skew, but not as noticeable.

The fix for this is to reduce the gap. I check the shaft of the hard rollers, relative to the plate tabs they sit inside at each side. There is normally a small gap, about 1 mm, above and below this shaft and the metal tab holding that shaft on each side. The rear side, more often than not, may have no gap below the shaft. The roller on that side will not have enough pinch and the paper will tend to drift as a result.

The fix I do which is fairly easy, is to remove the first screw on the top guide plate, front side and back side. It is the only one accessable without removing anything. The second screws holding this plate going towards the fuser are not so easy to remove. Leave those. What I then do is place my screwdriver in between the two plates, in the area where the screw used to be, and gently pinch the upper and lower plates together. Replace the screws and check the clearance of the shaft as noted earlier. Repeat until an acceptable gap is attained. Be careful as to not warp the entrance of each plate, like I said, be careful. The idea here is to level the pinch of the rollers and nothing else.

[sbillis]

......
The fix I do which is fairly easy, is to remove the first screw on the top guide plate, front side and back side. It is the only one accessable without removing anything. The second screws holding this plate going towards the fuser are not so easy to remove. Leave those. What I then do is place my screwdriver in between the two plates, in the area where the screw used to be, and gently pinch the upper and lower plates together. Replace the screws and check the clearance of the shaft as noted earlier. Repeat until an acceptable gap is attained. Be careful as to not warp the entrance of each plate, like I said, be careful. The idea here is to level the pinch of the rollers and nothing else.

Can you be more specific? Where is the point exactly you mention? any photos?

Also I would like to ask something more:
- Centering sensos (PF and ADU) must be on or off?
- 3mm gap from PF does it matters?
- FD,CD,Centering,Restart Timin must be done with A3 paper(11x17) or 13x19 or anything else customers using and what wheight.
- Skew can be corrected from ADU mechanical adjustment or from CD Skew software adj?
and maybe must importand
- Side 2 Lens adjustment must be ON for heavy stock? 300gsm with manual duplexing, does it matter?
or is effective only for auto-duplexing?

thanks and sorry for long questions

[Stirton.M]

Can you be more specific? Where is the point exactly you mention? any photos?

See the attached image....parts manual showing some parts of the ADU section entrance guide. The red circled screws are the ones to remove. The Green circled areas are where I mentioned I place my screw driver in between and then gently pinch the upper and lower guides just a little bit. When the screws are replaced back in, the gap between the upper and lower guides should be a little closer. The front side usually can be left alone, it is usually the back side that needs to be "tweaked". The blue circled items refer to the shaft and tabs I mentioned that have the 1 mm gap above and below the shaft as clearance. As I said, be gentle and sparing on how much you pinch the plates together. Too much pinch and you could introduce unwanted drag, which can also skew paper.

ADU sample..jpg

Also I would like to ask something more:
- Centering sensos (PF and ADU) must be on or off?
- 3mm gap from PF does it matters?
- FD,CD,Centering,Restart Timin must be done with A3 paper(11x17) or 13x19 or anything else customers using and what wheight.
- Skew can be corrected from ADU mechanical adjustment or from CD Skew software adj?
and maybe must importand
- Side 2 Lens adjustment must be ON for heavy stock? 300gsm with manual duplexing, does it matter?
or is effective only for auto-duplexing?

thanks and sorry for long questions

Turning off the censors is strictly optional. You can replace these if they are defective. There are service bulletins which have mentioned this in the past. Turning those off will eliminate the random shift, but at a cost. Image centering is automatic when they are on, but turn them off and the operator has to manually adjust front and backside registration. As mentioned elsewhere, you can adjust all the trays to center them all with each other as well as in duplex, but it is time consuming and not 100 percent. Especially since the LU202 or PF units do not have any mechanical adjustment for side registration. You have to electronically center the trays with duplex, and then you can mechanically adjust trays 1-3 to match the LU or PF unit, followed by tweaking here and there to center all the trays with each other. After that, the user has to tweak on a per job basis if they require duplex registration to be centered. It is a bear to do. Some techs would rather just replace the sensors, but from personal experience, I have found that doesn't always solve the issue. Glossy paper seems to be an issue with these sensors.

The 3mm gap does matter. In all cases, I have found this made the most difference when dealing with skews from the PF unit.

In all adjustments, I have used 24 lb 11x17. Generally, most shops would prefer you use the cheap stuff rather than the more expensive stocks. Keep that in mind when doing test prints when servicing. With the exception of course when dealing specifically with quality issues on certain stocks. I try my best to avoid using the expensive stuff where possible.

Some skewing can be corrected through the CD Skew adjust. Generally, if you eliminate the feed skew, you will likely eliminate any skew through the ADU, including duplex. The exception would be uneven pressure on any of the rollers as the paper passes through the unit. I've been fortunate. Of the dozen or so machines in my city, I haven't had any ADUs that had been 'warped' or bent, aside from the entrance guide I spoke of above. The specs call for a tolerance of 2 mm on 11x17 duplex where skew is concerned. All my machines have less than half a mm duplex. Auto skew adjust is off in all instances.

Side two lens adjustment is strictly a duplex function. The machine will not allow you to duplex weights above 257 gsm, you will have to manually refeed that stock, even if it is 100lb glossy text, which could easily pass through without issue. Some customers have "cheated" using this type paper. It works, but they run the risk of the fuser throwing an abnormal low temp code. Usually I just follow the service manual regarding which adjustments to make as I make them. There are prerequisite adjustments for various other adjustments, those should be performed for best results.

In the end, I have had the best results by trying to get the machine mechanically squared, and then after doing what I could there, going in and doing the electronic adjustments as needed.

Centering is about the only issues we sometimes have, but generally, the customers are quite content to use image adjust within the driver or CWS to compensate for side 1 to side two registration variances.