Control panel display is a blank gray screen, can not do a cold restart
because screen is gray can hear printer truning on but no display. Any
ideas
First thing to check is whether the engine test works.
1. The engine test button is located on the right hand side of the printer,
just below and to the rear of the control panel. You should see a small hole.
Use a non metallic object like a tooth pick and push the button that is behind
the hole. You should get a print with either a series of lines or a black page
(can't remember which is the correct one for this printer).
If it does not print a page, remove the formatter and try again. If it works
this time it is a formatter problem or reseating the formatter has corrected a
poor connection, so if it prints you should re-install the formatter and verify
that the problem is still there before you look for a replacement formatter.
2. If the engine test works with the formatter installed (1. above) then there
are several possibilities.
Remove the formatter, if the panel lights up the formatter is bad.
Check that all connections inside the printer are good and remove and replace
the formatter.
If not fixed the likely causes are...
Control panel cable (unlikely, never seen one fail).
Control Panel
Firmware
DC Controller
If you have another 4200 available or can borrow one, you could swap parts one
at a time.
3. If there is no test print at all then then the likely cause is the DC
Controller or power supply.
Sorry if this is a bit cryptic.
Let us know how you get on, if you would like the service manual I can e-mail
it to you but I will wait until you report back since it is a BIG file.
Tony