UJF-6042 MKII Losing White During Jobs

[julesk]

Hello, this is my first time posting.
We've had this printer since 2021. The printer is configured a PrCl YC MK WW. Recently head 4a is dropping out during jobs. If I run white maintain and immediately run a 15x18" job the white ink looks good over the whole job, but the next job will have hardly any ink. It will print for one to two inches before dropping out almost entirely. We had a tech here who ruled out it being related to the subtank by visually observing it going through a subtank maintenance cycle and checking the O rings on the connections leading into it. He also adjusted the positive air pressure with the needle valve behind the left door of the machine. The solenoid under the main bottle for the channel is actuating during prints and there is ink in the main tank under the bottle. He believes it is something electronic in the head, or possibly its cable, and this is corroborated by the fact that this head it not getting up to temperature while all the others, including the one in the same head assembly, are. Is there anything else you would look at before replacing the head? The way I interpret all this is that white maintain pushes ink through the head, and that as long as there is ink in the head it prints fine. I'd appreciate any insight.

 

[Smoke_Jaguar]

White ink circulation only happens in the subtank, as these are not thru-flowing heads. Try doing a subtank discharge and refill on head 4 and see if it times out on the subtank refill. While the solenoid valve (no needles in bottle system) might actuate, it can get clogged bad over time. Keep an eye out for Supply Ink errors. You can also flush the solenoid valve by clipping a syringe to the fitting on the valve, pushing it in and pushing/pulling the white ink back and forth to break up any potential buildup on the seals. Or just replace them, since they're like $25 (p/n M015864).

As for heating of the heads, something bizarre has to be going on for them to not heat up consistently. The heads are all plumbed in series and the water heater block system is what heats the heads. If one is clogged, they will all not heat and you'll get a code for the water pump. That said, a thermistor might be reading wrong.

Another thing to look at is doing a pressure test. Jog the solenoid open for heads 1, 2, 3, 4 and see how the pressure drops and recovers. If head 4 doesn't get to full pressure, could be a loose line, bad subtank or possible the pressure valve manifold assembly.

 

[julesk]

Hi, thanks for replying. It will discharge and refill the subtank without timing out. I just looked at the part of the service manual relating to the air system. I'd like to try the test you proposed although I think it can't be the only problem, because only head 4a is affected while head 4b has no issues.

Could you tell me how I would do the test? I don't know which pressure test menu to go in or really anything about the air system physically. I can search the forum about it since it probably has been discussed before.

To reiterate the symptoms, it will perform cleanings, subtank maintenance and white maintain without errors. The tech gave visual confirmation of the subtank emptying and filling. After any of those head 4a will print 2-3cc worth of ink before dropping out. Head 4b will print all day without issues.

The current theories I have are

1. that the subtank or head is clogged enough to prevent the ink from dropping through the head under the normal pressure
2. that somehow the particular subtank is under too much negative pressure and this is preventing ink from dropping into the head
2b. could somehow both white subtanks be under too much negative pressure but head 4a is clogged or not as hot and so it is harder for ink to flow into that head
3. that there is something about the circulation loop for that subtank that is causing too much negative pressure just in that subtank
4. that there is an active component in the head that pulls ink into its reservoir and that has failed

Do you think any of those make sense? Do the heads do something to supply ink to themselves or is it passive? Have you ever seen or heard of a head failing in such a way that it will always print a predictable amount of ink after a purge and then drop out? I'm thinking about just setting the print flushing level to something above 0 and seeing whether the problem goes away.

Do you know if the hot water path inside the head assembly is split in such a way that one head could fail to heat up? Is head 4 the first head in the hot water loop or the last; does it make sense for a clog to start there?

Okay, I feel like I have bombarded you with questions. I'm just really out of my depth and stressed about this.

Thank you

 

[julesk]

One other thing, in the manual I'm looking at it says

When run air pressure check, it will be a state where the ink circulation system is stopped. When resume the ink circulation system, manually resume after completion of the test.

I restarted the machine after going into the menu, is that sufficient to turn the circulation system back on? The tech has set it so the machine always boots into service mode. I don't see where in the menu to check whether it's enabled or not.

 

[Smoke_Jaguar]

Circulation is automatic with white ink sets, service mode just unlocks all the extra # menus.