Need Help FB700 - no yellow in beginning of print

[FulSnygg]

Have a problem with a HP Scitex FB700 that we can't figure out.
When you start to print it doesn't print yellow, but yellow slowly builds up so after about 3 meters it prints yellow as it should. It's like a gradient from transparent to yellow. When it finally prints yellow, it prints yellow as it should - if you print continually. If we let it rest for a while we have to start the process over again to get any yellow at all.
We print sheets in size 70x100 cm for test. First sheet: no yellow at all. Seccond sheet: start seeing yellow, especially around the edges. Third sheet: yet more yellow, still stronger around egdes. And so on. (See attached images)

We have tried the following things without result:
- Swapping ink pump
- New ink cartridge
- Swapping printheads
- Changing termistor
- New o-rings for the heads

We have done the test of air valves, turning on/off, and it sounds "click" like it should.

Vacuum pump sounds/works as usual, so we don't think there's any leakage in the air system.

There is ink in the head/reservoir.

Any ideas? We have opened a case at HP but no answers yet. Tech has no more ideas at the moment.

 

[danno]

Have you checked the inline filters above the thermistor? They are between the thermistor and the manifold.

 

[Boudica]

We are, as I type, having this problem with our HP 550. Thought we had a box of "underperforming ink", but after draining, putting in a new box and refilling the yellow - it worked fine for a bout 3 prints and now the problem is back. it's weird because it doesn't seem to lay down yellow for the first 3-4 inches - then it starts printing fine. I can't keep burning material.

HELP! What could be causing this? More importantly, how do I fix it?

 

[Boudica]

Have you checked the inline filters above the thermistor? They are between the thermistor and the manifold.

If there is a problem here, would it not lay down yellow at first, then suddenly start laying down yellow for the rest of the print?

 

[Riikkas]

Problem is the ink. HP ink for FB700 printer is very pad quality. We have had same problem with black, magenta and yellow. We order new ink box, drain old ink out and fill new ink in. Our suplier gives us the new ink box free (if old one is pad), but all this takes time and we cant use printer with pad ink...
And we have had this problem over a year now. Its every time pad ink, not once hardware problem.

 

[Boudica]

After replacing the thermistor, we found that it was the o-ring - not a good seal. Finally got it working again though.

AND we don't use HP ink anymore, haven't for a while now.

 

[Riikkas]

This is what we get with HP ink, 3 left prints are result of bad ink, 2 right prints are from new ink box (heads drained and filled with new ink). And this is sometimes with Black and Yellow too. I'm interested where to find reliable ink?

 

[Patrick Farrell]

In regards to no longer using HP ink. Who are you going through now? Just out of curiosity.

 

[Glavin_ID]

Nazdar is what we use and never had a problem.