My new JR 642 transmitter would run about 45 minutes before giving a low-battery alarm. Several other JR642 owners in our area reported the same problem. Testing the battery with my digital multimeter revealed that the transmitter voltage display was reading about 0.8 volts too low. I was lucky to complete two flights before the alarm sounded.
...
There was previously information here on how to adjust the JR 642 transmitter voltmeter yourself. I was contactacted by Horizon Hobby Distributors and asked to remove this information. This is due to the possibility of somebody screwing something up. I can understand their position, since many people nowdays refuse to accept responsibility for their own actions.
I was assured by the Director of Customer Service that units currently shipping do not have this problem, and that if you call them at 217-355-9511 you will receive prompt assistance. My dealer also confirms that the units they are receiving now are 100% OK. I have since purchased a second 642, and it is flawless. The programming buttons are even "snappier" and easier to press.
Watch out for those propellers!
...
My notes:
Of course you must know the actual battery voltage before you can adjust the transmitter display. It is important that you test the battery voltage with an accurate meter while the battery is under actual transmitter load. This is easy to accomplish by removing the battery from the transmitter, but not unplugging it. The probes of the multimeter can reach the contacts if the battery plug by inserting them in the same holes the battery wires enter. Make sure the transmitter is on while taking your reading!
Since even good multimeters are not 100% accurate, and since it is possible that the JR voltage display is not linear, I recommend being conservative by setting the JR voltage display a little low. I set mine 0.3 volts low.
I don't see any reason why a ESV that has a range for 9.6-volt batteries wouldn't work. The meter adds its own load to that of the transmitter, so make sure it is attached while adjusting the JR display. Have someone hold the probes on the transmitter battery connector for you.
Feel free to contact me if you have any questions.
September 04, 2002