Single horizontal band HP25600

[FooSchnickens]

We've just started having this issue with our press. Within the first foot of the print we will get a noticeable horizontal band across the entire width of the print.

The printheads appear to be fine as the test plots show that all but one or two nozzles are firing across all 6 heads. I've cleaned the rollers and vacuum holes in case it's a media advance issue but that hasn't helped. I've also run the printhead cleaning several times with no luck, either. I've wiped down the OMAS sensor in case it was not seeing the media correctly as it passed over. The printhead cleaning kit is at about 50% and all printheads are at 250ml usage or less as I just replaced them all about two weeks ago. I'm hesitant to think it's a media issue as I've been printing off this roll for a couple hours already and it's just now started doing this. It also worked fine yesterday with a separate roll with no issues.

Any thoughts or ideas? I've attached a photo of what's happening.

 

[P Wagner]

It is very unusual for an HP latex ink printer to do this. I've seen this on printers that use Epson printheads many times over the years. It is referred to as White Banding. How wide is the affected area (front of the band to the back)? Does it only happen once, or multiple times in a print?

 

[FooSchnickens]

So far it only happens once per print, within the first 12 inches. It's about 1.5" long but varies in its intensity. It ranges from barely noticeable without the use of a loupe to downright obvious like in the photo I posted. It's happened 5 times today so far and seems to be pretty random. It will go several prints without having an issue, then pop one out with this band. Most of the time the next print won't have it, but I've had to stop the job and start over several times from it doing it on back-to-back prints to save material.

Also, not that I think this would cause the issue, I double checked the carriage belt and position strip to be sure it wasn't dirty or damaged and all was well. We're also running the latest firmware update as of March 2013.

 

[P Wagner]

The first place I would focus is the substrate path. Perhaps a random error caused by a dirty media encoder in the left-side end bell?

 

[FooSchnickens]

You'll have to explain which piece you're talking about a bit. I'm familiar with most of the jargon but still clueless when it comes to some things and their proper names (well apart from doo-dad and thinger).

 

[P Wagner]

There is a round Drive Roller Encoder Disc at the left end of the drive roller. It has a sensor that reads the movements of the disc. Are you seeing any 56:10 errors?

It is in an area that would require an amount of dis-assembly to access.

 

[FooSchnickens]

Gotcha, that's probably why I've never seen it. No errors of that sort, the only one's I've ever encountered were pertaining directly to jams.

 

[omgsideburns]

Haven't seen it on my latex, but it happens on my UV. I get ink drop out like that when the vacuum pressure drops in my printheads for a second, like lower than it can recover from in the time it takes to make a pass or two. Different system though, so ymmv.

 

[FooSchnickens]

I spent some time Friday observing the press for a bit and compared the edge of an unfinished print (oh how I love jams) to the band and found that the pattern matches up exactly so it appears that the press is, indeed loosing pressure to the printheads, or the printheads themselves are going bad. I put in a support ticket this morning to see if HP will warranty the printheads since they're practically brand new.

 

[Kaiser]

What does your nozzle test show?

 

[Kaiser]

Haven't seen it on my latex, but it happens on my UV. I get ink drop out like that when the vacuum pressure drops in my printheads for a second, like lower than it can recover from in the time it takes to make a pass or two. Different system though, so ymmv.

I get this on a UV when there is a little air in the lines. Had an issue with the inlets on my magenta head that was causing dropout mid print.
Nozzle tests showed everything fine but if I started printing, Bam. Dropout. The inlet bracket was damaged. Apparently a factory dud. Head was replaced and everything was ok.

 

[FooSchnickens]

What does your nozzle test show?

All the nozzles but maybe two or three showed up in the test plots.

I talked with our supplier and they're going to warranty a new set of printheads for us. Should be coming in today so I'll swap them out and see if the issue persists. If it does I'll look into having a tech come out to check the vacuum system. We've had this press for just over a year so I hope this isn't a sign of things to come...

 

[FooSchnickens]

The saga continues...

The warranty printhead that HP sent us ended up being bad right out of the box, so they're going to try and schedule a tech to come out and take a look at it and also shipped out a new printhead. The second replacement head should be here today, and I sincerely hope it is soon becuase I've got 6 hours of window clings to run and our fedex cutoff is looming...