HP Scitex FB950 cyan dropping out...

[signman315]

I have a roughly 6 year old FB950 and the cyan drops out after about 8' of printing. The power supply, e box, and mother board are all about 1.5 years old. The heads are about 2 years old and showing very little issues (barely noticeable weak center jetting on 1 cyan and 1 black head). Here's the scenario....printing double sided coroplast, 4' x 8', fairly heavy ink coverage (roughly 80% coverage primarily black with yellow, and green design elements), printing using 600x300 bidi....first side of sheet prints perfectly, last 20% of second side the cyan completely drops out but all other colors are good. From that point on cyan is dropped out. I've cleaned and purged all print heads, I've also emptied the cyan and light cyan heads (aka filled with air) then refilled them with ink. Upon purging or emptying/refilling I can print another sheet but with the same results. Once the cyan drops out then it takes a purge or empty/refill to bring the cyan back.

I'm not getting any warnings popping up. Prime bars look good also. But I did have a warning after the printer sat for the weekend saying the ink system has been disabled due to it getting too cold. Though I've received this message once before I did not experience any issues. It's warm now, the warning is gone, and I've actually used a small heater to warm up the ink cartridges but with no change in the problem. The lowest the temperature got was between 40-50 degrees fahrenheit. Any insight would be much appreciated, thanks folks!

 

[GP_Oz]

Swap the ink thermistor from C to K run test again.(remember to also swap cabel positions)
Could be a call for ink problem, where it thinks it has ink..so doesn't ask for more.

Im not always convinced by the error reporting on the 950s or 500/700s.

There is a few other tests but based on your write up id try that first. Really quick and will tell you a bit.

 

[signman315]

Thanks GP_oz I'll run that test and let you know what my results are. I may have a question or two regarding how to go about it, but I'm going to wait until tomorrow to dive deeper. Thanks again!!

 

[signman315]

Swap the ink thermistor from C to K run test again.(remember to also swap cabel positions)
Could be a call for ink problem, where it thinks it has ink..so doesn't ask for more.

Im not always convinced by the error reporting on the 950s or 500/700s.

There is a few other tests but based on your write up id try that first. Really quick and will tell you a bit.

So just to clarify...when you say "remember to also swap cabel positions" do you mean swap the positions of the data cables that run to the head? Or just be sure to swap the cable positions of the ink thermistors on the head board? Thanks

 

[GP_Oz]

The thermistors, sorry i was unclear.

To further expand..there is 3 in total.
2 ink and 1 air.
Only need to change the ink ones around.
There will be one in K and one in C.
The 2 colours share the air thermistor. It is preferred to have the air thermistor in the cyan...or the further away from lamp(same on the lc/lm set)

 

[signman315]

The thermistors, sorry i was unclear.

To further expand..there is 3 in total.
2 ink and 1 air.
Only need to change the ink ones around.
There will be one in K and one in C.
The 2 colours share the air thermistor. It is preferred to have the air thermistor in the cyan...or the further away from lamp(same on the lc/lm set)

Thanks for the help...I'll run the test and let you know how it goes. Really can't thank you enough, cheers!

 

[GP_Oz]

No worries
950 engineers are a dying breed...like in Higlander I consume their souls until there is only 1.

It may come down to other parts, but this test will give a good direction to head in.
Good luck, be careful parts are rare.

 

[signman315]

No worries
950 engineers are a dying breed...like in Higlander I consume their souls until there is only 1.

It may come down to other parts, but this test will give a good direction to head in.
Good luck, be careful parts are rare.

HaHa! Loved that show Highlander....by the way things are going you and I will be dueling it out for the last soul haha!

Anyway, switched the thermistors and did see an improvement in cyan (turns out it's actually light cyan, so I'm working with the LcLm set). But I have not seen the dropout in the Lm head that I switched the thermistor to. I've ran a number of test prints and can't seem to get the problem to manifest itself in either the Lc or Lm. So I will wait a few days and see what pops up, if anything.


One thing to note, when I pulled the thermistors they did have some ink on them, and there was a fair amount of dried ink built up around the base of thermistor (where the glass piece meets the threaded metal). A tech told me that he's seen similar issues on other model printers where ink build up on the thermistor causes problems. So anyway all seems to be well for now. I'll post back here as I find out more. And of course BIG THANKS!

 

[GP_Oz]

Good to hear you are on the way to getting a fix.

Sometimes the internal seal on the thermistor falls down and sits on the end of the glass...giving a false reading of ink being in the res.

If you need a set of thermistors (3 piece matched set) and cannot source them, drop me a line and ill hit the boss up for a special price. We scrapped the last 950 here about a year ago so the parts are pretty much useless to us.

 

[Chiprinting]

I had a 950 a few years back and it would do the same thing when printing heavy coverage the thermistor seldom fixed the problem, what I determined was the head drivers got too hot and started shutting down. I moved the fans maybe added bigger ones don't remember. It helped a little but it seems inherent to that printer.

 

[signman315]

I had a 950 a few years back and it would do the same thing when printing heavy coverage the thermistor seldom fixed the problem, what I determined was the head drivers got too hot and started shutting down. I moved the fans maybe added bigger ones don't remember. It helped a little but it seems inherent to that printer.

Thanks for that insight, I agree to some degree. Although in my case the thermistors were really caked up with dried ink, since I've cleaned them I literally haven't had a single issue and have really put the machine to the test with heavy coverage prints. Although I'm certain the problem will rear it's head again at some point. I'm certainly no technician but my hunch is that some thermistors were dirtier than others and this caused uneven readings throughout the whole set. That could be off base but since I've cleaned them haven't had any troubles. Thanks again, I'll post some updates if I gather any more info

 

[wunder]

Normaly the thermistor is not possible to give this error.....thermistor can give empty or full Reservoir signal....nothing to do with them.....to solve the ink problem on cyan are two ways.....

1st.....the Festo 3way valve on the backside of the carriage.... What they do.....1channel vaccum, 2nd airpressure..... So they cant hold the vaccum means a airleak by refilling ink....change this with other one like black or magenta.....and check out the changed color.....

next..check or renew the airfilter on the vaccum tube........