Hi Piet,
Unless you are a qualified and experienced technician on the 4900, the problem might be you, not the printer. The Service Manual is not a substitute for training and experience working on those machines; it takes very little error to put them off completely. I think you should start by calling Epson Tech Support for advice (phone support is usually free regardless of warranty expiry); if they recommend you bring in a certified technician to reassemble it all for you, this could well be your best option.