HP 940 Printhead problems..!

[websnail]

I am going to order it then a see if it helps. I have also see a next type on ebay, this one claims to be better:

http://www.ebay.com/itm/HP-940-88-p...=350578512699&ps=63&clkid=1684848157865908075

I had a look at the first kit a bit more carefully and the one you just linked to from eBay and noticed a couple of things you might want to check on.

1. The first kit is more involved with that split funnel creating a very real potential ink spill/mess that is hard to ignore. Bit concerned they went that route as it's just asking for trouble. I neglected to spot the funnel before so mea culpa and a withdrawal on my whole "DIY" suggestion...

2. The second kit with tubes is a more elegant solution on that front but the lack of attention to the description makes me think it's a reseller with very little clue as to the actual kit itself so I'd look for an alternate purchasing source for the same thing. The key things you'll want to check for are:
- length of those tubes
- can the tube be flexed to dip into a bottle of ink so you can reprime
- any instructions you can check out first so you can see how they work
... without that I'd have some qualms about the suitability of the kit without needing to do some retroactive modification to make the whole thing workable.


All in all, nice ideas there but I can't help but think the whole lot could have been put together and thought through somewhat better...

 

[ink-solutions]

I will just buy them both an see which one works best.. Tell me this, do you think that the CISS with the pump is better than the one without ? i know that i have asked this question before, but the answer that i got was not very clear..

 

[websnail]

I will just buy them both an see which one works best.. Tell me this, do you think that the CISS with the pump is better than the one without ?

It's a tough call... The pump is there for a reason it seems so my preference is for a unit that has positive pressure and the bulb/pump built in. That said you have to be careful that the pump is good quality and not going to fail and/or degrade as that can happen. I would personally recommend converting some OEM cartridges to use a reservoir (located slightly above the printhead), ensure they are primed to remove air and go that route.

The non-pump/bulb systems will work ok and seem to be fine for many that use them but you have got to be keeping an eye on the ink levels and ensure they don't leak.

i know that i have asked this question before, but the answer that i got was not very clear..

Sounds about right... there's no definitive...

 

[websnail]

Did a little more digging about this today as I have three L7780/7680 printers to revive at some point soon and discovered that there's a few videos that show you how to clean out an HP88 printhead and get it all working again...

Vimeo and Youtube are your friend it seems...
http://vimeo.com/35345649
http://www.youtube.com/watch?v=y6YjL7mff5c

 

[Pcarsba]

I am following this thread with interest since my 8500A stopped working. Short history: I refilled all 4 cartridges with pigment ink (NanoDigital) and all colors have issues. Black clogged first and subsequently all other colors at one point or another have streaks (fading lines). The printer goes into these infinites cycles of trying to clean and align print heads and I can only stop hat by going into these hidden menus either doing a full reset and/or disable pen alignment. In the process if sucks ink like a drunk.

My new strategy is to open both print heads, flush out the crappy pigment ink and switch to dye ink. Watched the videos and also found some reference to weight of a full print head. Mine both weigh in at 56 grams so I don't think I have an air issue.

What I am not clear about is the pumping of the air bags in h head. One video didn't show it while he other did. I also read the detailed tear down on the CIS forum. There it sounded like the bags have a set volume and are sealed. Any comments and/or experience here?

 

[websnail]

I'll be honest I don't understand the air pumping side of things either... I suspect it's going to be a case of taking a hard apart myself at some point and getting dirty...

 

[The Hat]

I'll be honest I don't understand the air pumping side of things either... I suspect it's going to be a case of taking a hard apart myself at some point and getting dirty...

Websnail did you mean to Say taking a HEAD apart Patience

 

[websnail]

LOL... pedants of the world unite...

Hmm.. is that right? Should pedants be treated as a noun or capitalised to emphasise their intrinsic being?... [/irony]

 

[Pcarsba]

I got several used heads on its way thanks to evil bay. My best explanation today is that the air bags are just another way to compensate for a varying volume of ink in the head and at the same time provide a shut off mechanism to cut supply when fully deflated (head full)

The pumps in the printer carts pump ink at some small positive pressure into the heads. That deflates the air bags through a vent hole at the top and shuts the valve in the head. If that is the case the plunger acting on the cart pump just feels resistance. All is happy. Once the plunger doesn't sense resistance it will trigger the "ink depleted" message. I confirmed this by the following:

Just placing the front portion of a cart with chip into the printer will give the empty message. However, when in keep pressure on the extending plunger the printer assumes there is a working cart present and it will start printing.

 

[Pcarsba]

Here are some findings and wild guesses after having taken a couple of heads appart:
- the weight of heads can vary greatly. Empty they weight somewhere in the lower 40gr. The used heads I got are anywhere from 49 -57 gramms. Once you really fill a head with ink it can get as heavy as 65 grams. I will get exact numbers when do some more.

- The lower part of the head must have some sort of filter system that is more than just a layer of cloth. It almost looks like porous block. I will cut one of the dead head open to get some clarity

- The air bags are open to the environment through a vent hole. When they inflate they compensate for lost ink volume and open the inlet valve to allow ink to enter the head. The steel beads act as a check valve. The springs on the air bags ensure the air bags don't just inflate when ink tries to flow out of the nozzles - they prevent the head from leaking ink by creating an ever so slightly lower pressure inside the head compared to the environment. In other words the ink flowing out through the nozzles leads to expansion of the air bags and work against that spring.

Once the head is open (top removed) it simply leaks all ink out the nozzles by gravity alone.