Error light stays on

Clear the Error Log: a. Turn the printer off. b. Open the front cover. c. Hold down both buttons while powering on. d. Release the buttons when the error light stays on solid. e. Close the front cover.

My sollution was this:
I had 2 same printers (1700n), one was fine other was not.
On both printers I opened right-side cover. I checked the boot procedure (lights flashing on both.
Then opened the cover on the good printer and had exactly same effect as faulthy Printer.
I removed the Front cover switch-connector from motherboard of the bad printer and plugged in the one from the good printer as a test. (for this I had to gently remove the iron cilinder around the group of wiring to make the wire of the switch reach the other motherboard, also removed main powercord from good printer, just in case). The faulthy printer worked fine again !
Finally I put everything back in place: I removed power from repaired printer and moved the pins (just a little bit out of center) on the motherboard.
In other words: there was a bad connection/contact on the frontcover-door switch to the mobo.
I've seen this kind of faults before in old equipment.

I hope it helps more people repairing old junk.
Cheers, Radegonda.