If the seed monitor on your planter, or one section of the seed monitor on your planter, mysteriously goes blank, be suspicious of a problem with the seed sensor for just one row. If a seed tube sensor shorts-out internally it can back-feed and "kill" the seed monitor for the entire planter.
The quick diagnostic routine to check for that problem is to unplug all the seed tube sensors, then plug them back into the main harness one at a time. The seed monitor display should come back to life when the first good sensor is plugged in, and continue to work until the faulty sensor is connected and kills the entire system again.
I ran into a variation on that problem this spring, when a farmer who had been fighting problems with his seed monitor for three planting seasons finally asked for help in diagnosing the problem. He said that his seed monitor would intermittently go blank, maybe for half a round, then come back on and work fine for 10 or 15 rounds. This spring, however, the problem got to the point where the monitor was blank most of the time.
Long story short, I found a zip tie holding the 3-wire harness that connects the main backbone wiring harness to the seed sensor on row #7 had broken three years ago, and that harness had drooped and been nicked by the sharktooth row cleaner for that row. Whenever the bared spot in the wires rubbed together or brushed against the metal frame, the entire monitor system went off. It took 30 minutes to diagnose and 5 minutes to fix a problem that had annoyed that customer for three years.
And...if it sounds like I'm bragging about my diagnostic prowess, please refer to the blog about humility that I posted last week.