MP500 again - purge problem?

[The Hat]

There is one other thing to try that might work also and that is to clean the timing wheel that’s mounted on the extreme left hand side of the printer, it may have picked up some ink or other foreign matter, I would say just clean the one side to see if that makes any difference (No need to remove the top cover)

 

[Robert the Bruce]

Thanks @PeterBJ , now I understand the pattern of missing ink across the page.
I always use OEM cartridges refilled by my local Cartridge World branch. I do not know what ink they use, but it has served me well in the past. I have only had two 'dud' cartridges before out of a sample of scores and scores (both PGBK) - one where the ink didn't flow properly, and another where the chip was falsely reporting the ink level as empty when it got down to about half full.
Presumably I should clean out the blocked ink tubes in the head by gently squirting cleaning solution through the ink ports using a syringe. I have done this before, but I know you have to be careful, as it can rupture the tubes inside.
Is it possible that there's a problem with the seal between the cartridge and the ink port on the head? There seems to be a circular rubber gasket there, and apparently you can get replacements with some ink kits. How would I go about checking if there's a proper vacuum being formed there? I have wiggled the cartridge around, and tapped it and re-seated it several times after replacing it, but it didn't seem to make any difference.

 

[turbguy]

Yes, the rubber seal can cause issues,but it is really there to prevent the ink from drying out on the exposed part of the sponge at the cart outlet.

You may have a stubborn clog in the printhead passageways. This can occur, particularly with PGBK ink. I've had to use some pressure on the ink inlet with a turkey baster bulb to clear some stubborn clogs. BUT, you gotta be careful you don't damage the nozzle plate with overpressure. The internal passageways in the plastic portion of the printhead are fairly stout.

You should be able to force air and windex through the ink inlet and out the nozzles...

 

[PeterBJ]

...I always use OEM cartridges refilled by my local Cartridge World branch. I do not know what ink they use, but it has served me well in the past. I have only had two 'dud' cartridges before out of a sample of scores and scores (both PGBK) - one where the ink didn't flow properly, and another where the chip was falsely reporting the ink level as empty when it got down to about half full...

As the cartridges are refilled using an unknown ink and refill technique, and possibly not purged even if they might need a purge, I strongly suggest to try a new Canon OEM cartridge before attempting to clean the print head that might actually be perfectly OK.

Cleaning the print head outside the printer is always risky; you risk not only to ruin the print head but also the logic board in the printer, making the printer a total loss.

Water left where it does not belong, behind the the ribbon cable and circuit board on the back of the print head is the worst risk. It can create a short or leakage current that ruins not only the print head but the logic board in the printer as well. A logic board that has been damaged this way, can ruin a new print head, so it is extremely important that no water/cleaning fluid is left where it does not belong, the print head must be properly dried before re-inserting and testing to avoid this risk.

 

[Robert the Bruce]

I have run out of cleaning solution, so have just ordered some more which should arrive in a couple of days.
When it does, I think I will try to clean out the PGBK passages in the print head. After soaking I always make sure it is properly dry before I put it back in the printer, by using kitchen paper, then blotting paper on the body, circuit board and ribbon cable, and then leaving it to dry for a few hours. I also clean the contacts on the head and in the printer with solution, then leave those to try for a while too.
I will report back when I've done this. I'll also examine the rubber seal around the PGBK ink port for any defects. I wouldn't expect a problem there as it's a relatively new print head (at least I only installed it last year; I've no idea how long it had been sitting in its original packaging!)

 

[Robert the Bruce]

Well I tried it - no luck :-(
Having filled a syringe with cleaning solution, I pushed it gently through the PGBK ink port until it trickled out of the nozzles. I then dabbed over the whole head with kitchen paper and blotting paper, and left it to dry overnight.
I replaced the head and cartridges, and did an initial clean followed by a nozzle check. All colours were fine (not surprisingly, as I didn't touch those ports or nozzles), but the PGBK pattern was very washed out and in parts missing.
I then did another clean and nozzle check. This time the PGBK was completely absent. Further cleans produced no improvement.
As a last resort, I left the head in cleaning solution overnight, flushing the PGBK port before and after, then drying and replacing again.
Same result - poor initial PGBK check followed by complete absence.
So, I seem to have made matters worse. Where now?

 

[turbguy]

I would suspect you still have a stubborn clog in the print head, OR there is an air leak somewhere between the cart outlet and the nozzles. IF your nozzle check shows ANYTHING, the nozzles are firing. They are using residual fluids in the nozzle as "ink". In my experience, pigment inks can form VERY solid clogs that can be VERY stubborn.

What I would do with this situation is HIGHLY RISKY!! YOU MAY RUIN THE PRINT HEAD! I would remove the two screws from the nozzle plate (one or both may or may not be left-hand threaded), carefully pry up the nozzle plate and metal heat sink (hopefully they stay glued together), remove the "funny" elastomer gasket that joins the plastic head to the nozzle plate, then flush fluid through the assembly's passageway to assure a clear path. Then inspect for large clogs in the nozzle plate. Then re-assemble, dry (if required), and retry printing.

 

[Robert the Bruce]

Well, I finally got round to doing what @turbguy suggested. Disassembling the print head was easier than I thought.
I didn't notice any particular clogs, either in the assembly or the nozzle plate, but I flushed everything on the PGBK side out with cleaning solution just in case.
Put the whole thing back together, dried and returned to the printer....
...and it was recognised OK! Thankfully I hadn't destroyed it.
Unfortunately it hasn't solved the problem - all three colours & photoblack are still working, but nothing from the PGBK nozzles.
Is my only option now to get (another) new print head?

 

[Robert the Bruce]

Oh I took some photos during the process. I will post them if anyone would find them useful.

 

[The Hat]

Oh I took some photos during the process. I will post them if anyone would find them useful.

Yes please..