I9900 Carriage Problem

I disassembled the i9900, like I've had to several times before, to reattach one of the purge unit tubes. This time, when I tested it, the print head carriage moved to the left and stayed there. The error code is two blinking lights. The Service Manual indicates there are several possible problems:
Carriage Unit
Timing Slit Strip Film
Logic Board assy.
Carriage Motor

I don't want to invest too much more into this printer, I've purchased a P-100.
But, I don't want to toss it, if the problem can be fixed easily.

Any way to narrow down the problem to one part. I'm not even sure Parts are available. I just spent a lot more than I ever did before for a new print head that's still in the sealed bag.

The behaviour of the print head carriage indicates a problem with reading the timing strip to me. Was the timing strip removed when disassembling the printer for the purge unit repair? If so, maybe it is not properly attached. The strip must be properly positioned to function. The timing strip has an "L" marking which must be positioned at the left side and read as a proper "L" when viewed from the front of the printer. The strip must also be threaded properly through the optical reader in the print head carriage.

Maybe the timing strip is contaminated with ink? It can be cleaned using soft tissue paper wetted with a window cleaner with ammonia. With the printer disconnected from the mains you should be able to slide the print head carriage from side to side to allow cleaning the whole strip.

Peter, thanks for the reply.
No, I've never had to remove the timing strip to get to the purge tubes. I do have to tilt forward and lift the unit away from the lower case to get to the tubes that are under the vacuum pump.

I tried cleaning the timing strip with ethanol and cotton swab as instructed by the service manual before I posted this plea for help.

I wonder if the purge unit could be the cause of the problem even if the error code indicates otherwise? You could try if the purge unit parts intended to move does move freely. I have experienced a problem with the purge unit in an iP4000. The printer would not print and gave an error message, I don't remember which. After cleaning away old ink and gently pressing on the purge pads something clicked into place and the printer worked again. I don't remember if there were problems with the print head positioning.

A window cleaner with ammonia or even plain tap water is a better cleaner to remove ink than concentrated alcohol, both ethanol and isopropyl alcohol. A 20% alcohol in water solution is also a good cleaner, but the concentrated alcohol is not. Concentrated alcohol tends to extract water from the ink making it less soluble.

I wonder if you disturbed some connectors when you repaired the purge unit. The print head carriage connects to the logic board via one or two ribbon cables. You could try to gently wiggle these cables and test if they are properly attached both at the print head carriage and at the logic board.

If these suggestions don't work, then I'm out of ideas.

Peter, I wish it were as simple as reassembling the printer again. I checked over the connections (there's a bunch) and didn't see any that were obviously misconnected. I'll look again and maybe try disconnecting/reconnecting the carriage cables. But that will be in a while. Now it's time for a nap. It's been a long day.
Thanks again for your help and advice.