Cannot change prices on any of the signs is either the transmitter (hand held) is defective or the receiver (Master control board) is defective or the Antenna is lose or defective.
If the price can be changed at a range less than 10 feet then there is either RF interference or the antenna is defective. To check for interference turn off all lights and other electrical items in the close proximity to the sign, if the remote now works one or more of the lights or other items that were turned off are defective or causing RF noises causing the price sign to lose communication.
If turning off the florescent back lights fixes the problem replace ballast/light bulbs as required to eliminate the electrical RF interference.
If an electronic reader board is turned off and the problem is resolved, order two 5’ antenna extensions and install from the antenna jack to any point as high as possible away from the reader board, do not add the antenna, check communications as the antenna extension is moved to gain the best reception, mount the extension in a location that allows for the best operation.
If the price cannot be changed at any distance check the battery (this should be standard showing where the battery is how to check it and how to remove the battery and how not to remove the battery.)