MP500 again - purge problem?

[Robert the Bruce]

Hello all,
I started a thread last year about problems with the pigment black on the print head of my Canon MP-500. As detailed in the thread, I managed to largely solve the problem by replacing the print head, and then soaking it several times in cleaning solution to get the ink to come through. I also had to take the machine apart to clean out the waste ink pads after all the cleaning cycles I had run!
A week ago the black printing started showing missing lines. Doing a basic clean from the printer's Maintenance menu would appear to solve the problem according to the nozzle check pattern, but black text would still show banding, and then on printing further nozzle check patterns missing sections would appear again.
Yesterday I removed the print head and soaked it in cleaning solution overnight, but it doesn't seem to have made any difference.
I am now wondering whether the purge unit is functioning properly. My first thought is that there is a problem with the seal between the head and the rubber gasket over the capping station. When I put the machine back together last time, I did notice a slight crack in one corner of the rectangular section used to seat the pigmented black nozzle section of the head, but thought I had managed to correct it last time using the tip of a soldering iron! Perhaps there is a slight leak which is preventing a vacuum being formed.
How would I go about verifying this, and then fixing it if necessary? It has been suggested to me (by someone who is not a printer engineer) that I might use rubber solution glue, as found in bicycle puncture repair kits. Is it possible to obtain a replacement gasket? I have searched exhaustively online and been unable to find one.
So far I have not taken the cover off to get a proper look at the gasket....

 

[Robert the Bruce]

I should add that there doesn't seem to be a problem with any of the other colours (Cyan, Magenta, Yellow or PhotoBlack), but of course those use a different section of the rubber gasket.
But colour prints don't come out properly either, as it seems to use PGBK ink in those as well!

 

[stratman]

Turbguy's instructions on checking the purge system: http://www.printerknowledge.com/threads/urgent-help-canon-ip4920.7972/page-4#post-66333.

Service manual and parts catalog: http://www.printerknowledge.com/thr...post-them-here-sticky.5071/page-13#post-66572.

You might find parts by cannibalizing a printer found on eBay or Craigslist.

 

[turbguy]

The entire purge unit is a replaceable part, but not the gasket itself. You will have to get one as Stratman suggests, IF that's the problem. Sounds like it could be a cart problem. Try a different PGBK cart first.

Typically a purge unit issue manifests itself by sudden loss of a whole color or all PGBK ink, normally after a cart change.

 

[PeterBJ]

The parts number for the purge unit for the MP500 is QM2-2295-000 and for the iP4200 that uses the same print head it is QM2-2208-000. In the parts catalog the units look very similar, and I saw somewhere on the web that they share a common alternative parts number QM2-3641-000.This suggests that they are identical.

I have a couple of Pixmas 4200 and some defunct Pixma 4000 I only keep for spares. The gasket and the porous plates look to be identical for the Pixmas 4200 and 4000.

The gasket and plates from the Pixma 4000 look like this, on the bottom side the gasket is marked 1-60:

For proper function of the the purge unit the porous plates must be inserted correctly into the gasket. Note that the cut-off corners must be placed in the upper left corners of the gasket and also note the 4 small lips to hold the rectangular plate and the 6 small lips to hold the square plate:

If you promise to report success or failure, you can have the parts for free. You can use the forum conversation system to send me your Email or postal address, I can then put the small parts into an envelope and post it to UK.

 

[Robert the Bruce]

Thanks @PeterBJ, I might take you up on that offer later.
Meanwhile, the problem gets stranger. As @turbguy recommended, I changed the cartridge (actually to a cleaning cartridge I use for testing - containing a mixture of ordinary PGBK ink and cleaning solution). Now I get perfect nozzle check patterns (i.e. all segments present) but text documents still print with banding on some lines. This effect makes some lines unreadable, so I need to solve the problem soon. I also get this on test pages printed from the computer. Reverting to the original cartridge produces the same result.
I did notice that three of the segments in the PGBK test pattern aren't quite aligned (they form a sort of 'step up, step down' pattern) but that has been the case since using this new print head. It produced slight inaccuracies around letters before, but not this effect of missing lines of print.
Is there anything I can do beyond the usual nozzle checks to work out exactly what's going wrong?
BTW I did a manual print head alignment after replacing the print head in its cradle today, in which three patterns needed minor alteration. It produced no noticeable difference to the nozzle checks or document prints.

 

[turbguy]

A nozzle check uses very little ink, so the ink flow rate between nozzles and cart is very low. Text printing is a larger flow rate. It sounds as if the nozzles are being starved during text printing. Does the defect get worse as the printer prints further down the page? If you purge unit was defective, there would probably be NO text printing at all (nor any PGBK nozzle check).

 

[PeterBJ]

Could you upload scans or photos of both a nozzle check and a text document showing the defects?

It is often said that a picture is worth more than a thousand words, and I think it is certainly true when discussing some printer problems, like this one.

 

[Robert the Bruce]

Here are two scans, first the nozzle check, then text (from a Windows test page print; the results for text documents such as letters are similar)

 

[PeterBJ]

The text document shows ink starvation in pigment black. It is most clearly seen in the headline "Printer Test Page". Note the wedge shaped areas of missing ink. It shows that the ink starvation gets progressively worse as the print head travels across the paper. The reason that some of the wedges have the "tip" to the right and others to the left is that the printer uses bi-directional printing.

Two things can cause ink starvation, the cartridge and the fine ink channels in the upper part of the print head. Hopefully it is a cartridge problem.

Even if it is expensive, I suggest to try printing with a new OEM PGI-5 PGBK cartridge. If the error goes away, then the pigment black cartridge was the problem. If the error doesn't go away, you know that the error is in the print head, which will then need some cleaning.

Only Canon OEM cartridges are recommended for refilling. Compatible cartridges often cause ink flow problems if refilled and sometimes also when new. So what kind of cartridges do you use and if you refill, what brand of ink and what refill method do you use?

I think the purge unit can be ruled out as the cause of the problems, as all the PGBK nozzles are working in the nozzle check, but fail when the are starved of ink. The text document demands more ink than the nozzle check as stated by turbguy, and so shows the error that the nozzle check fails to show.