I am programming an interface for an 86142A OSA. One day, the screen failed (no menu or booting display); the only way to get the measured spectrum is to plug an external screen via VGA port. Please, I want know if itâ€™s a programming mistake or hardware failure. Also, can you give me the remote GPIB command to turn the display back on the unit?
I'm glad I just found this topic, as I was about to post about the same problem on the same kind of unit.
I have not yet attempted the commands listed but I will.
First thing: When my unit is powered up, by shining a flashlight at the dark screen, with overhead lights turned off, you can faintly see the display images. This indicates that the LCD display is getting data. The problem is that the CCFL lamps are not operating.
In this unit, there are two CCFLs which are driven by a separate inverter for each one. Failure of both inverters and/or CCFLs at the same time is dramatically unlikely.
The low voltage power input to the inverters is routed through a ribbon cable from a main board in the unit, to the front panel keyboard PC board, and from there to the inverters. If all of the keyboard controls are working normally, you can all but rule out the possibility of a connectivity issue. Possible, but really not likely.
Two possible failures remain: A component failure on the main board, or a software issue or command that's keeping the inverters from getting a drive signal.
I do not yet have a service manual for this unit and have not explored in greater detail than I have described. I'll attempt to use the described commands and see if that brings back the display. If not, then I'll be looking for maybe a blown regulator on the main board, which I presume will lead to the CCFL inverters.
Incidentally, if you have any test equipment with a dark LCD display, you can check for LCD operation as described earlier. New CCFL lamp tubes can be purchased from ccfldirect.com or other online sources for a few dollars each, and retrofitted into your LCD panel in about 15 minutes of careful work. It's not tough to do.
Inverter modules are usually OEM types that can be easily replaced with an identical or at least workable replacement for under 20 dollars each.
I LOVE finding test equipment that's for sale cheap due to a dead LCD display. It's rarely more than a 20 dollar fix, in parts cost.