If you mean that there is a complete drop-out of PK and VLM, this means there could be an air blockage affecting those two channels, or something larger than usual causing an ink clog. As you have already tried the normal cleaning procedure twice and did not resolve it, you will need to resolve to "Clean>Powerful" but do it only for the nozzle pairs having those two inks, not all the colours (wastes a lot). After each "Powerful" clean, run a print through the printer that exercises those channels and the other channels in the pairs. You can go to the website of Marrutt USA, Epson 4900 maintenance, and download their colour files for doing this. It is important to run the prints between Powerful clean cycles. So your sequence of actions will be: Powerful clean, run a nozzle check to see whether they are unclogged yet, if not, run a print with the colour pairs concerned, then do another Powerful clean. Then a nozzle check, etc. Run through this procedure of clean-check-print up to three times in one day - no more. If after three replications of this cycle the nozzles are still clogged, shut the machine overnight, then go back to it the next day and retry the same cycle. If after another three replications the next day you are still having a problem, call for a qualified technician. DO NOT use stuff like Windex or Simple Green or any ammonia-based solvent on the printhead - this can destroy it. There are people on this Forum who disagree with this warning, but I have this advice from very senior, responsible people within Epson.
