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Help, reversed charger polarity

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Old 12-28-2004, 01:00 PM
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savoy
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Default Help, reversed charger polarity

While setting up a new NIMH battery and charger for my JR 652 TX I reversed the charge jack polarity. After an over night charge my TX is now dead. Any idea what damage I caused to TX and/or battery pack. Thanks
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Old 12-28-2004, 01:19 PM
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ChuckA
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Default RE: Help, reversed charger polarity

You are just the latest victum of JR's refusal to abide by accepted standards. For at least 50 years, and probably 100 years, the standard for this type plug has been center positive or signal while outside has been negative or ground. This is one of the reasons I quit JR years ago. I don't trust any company that doesn't know how to wire the charging plug. Chargers such as the Sirius Charge will protect you from this mistake because they will not work if the polarity is wrong.
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Old 12-28-2004, 02:00 PM
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mr.rc-cam
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Default RE: Help, reversed charger polarity

Inspect the pack for overheating damage. If it looks good, place it on a low tech C/10 slow charger for 20 hours (do NOT use a fast/peak charger). Then properly cycle it and recharge again. If the offending charge rate was low, the pack should come back to life (may take a couple of cycles).

You may have gotten lucky and blown the internal fuse. If that is the case, install a new 3A 5mm fast blow and you are good to go.
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Old 12-28-2004, 02:01 PM
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will
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Default RE: Help, reversed charger polarity

Don't panic. The transmitter is probably ok.

Take the back of the transmitter case off. Be sure to remove the crystal and the battery pack before you try to lift off the case. Don't tug on the battery connector. Simply take a small screwdriver and insert it between the battery plug and the transmitter receptacle. Put the screwdriver blade on the side that's facing towards the center of the radio. Gently pull the battery connector and it'll will disconnect easily.

Look at the center of the radio and down to the circuit board that the transmitter battery compartment was installed over. On a small circuit board, right above the long green board where the battery tray would be, is a fuse. The rating is 3A and its size is GMA. The fuse is blown. A replacement may be purchased at Radio Shack. After replacing the fuse, install the crystal and the battery pack and test the radio.

You will probably have to charge the battery overnight with the factory charger, to test your repair.

If the radio display does not come on or the radio doesn't work the receiver, the diode is blown. The diode is located right above the fuse. Look for the diode symbol. That would be an arrow with a line drawn in front of the arrow point. That repair may be beyond your skills. If so, you'll need to send the transmitter in for repair. If you have to ask how to remove the diode, it's time to box it up.
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Old 12-28-2004, 03:12 PM
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savoy
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Default RE: Help, reversed charger polarity

Thanks, I checked the fuse and found the battery pack dead, fuse ok. Put the old pack back in and radio works but memory is gone. I thought the on board batt would have kept the memory. I wonder if its time for new on board batt, its going on 4yr. Can the lithium batt be changed or must it be sent in. Since my memory is gone now would be the time to changed it, thanks again.
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Old 12-28-2004, 03:38 PM
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will
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Default RE: Help, reversed charger polarity

Great! Your pretty lucky. Both times I've done that trick, it cost me a fuse.

The backup battery is soldered in.
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Old 12-28-2004, 08:27 PM
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Default RE: Help, reversed charger polarity

Wrong. I have a Sanyo adding machine that uses the same center-pin-negative plug. I have seen phones, calculators and other gizmos that used the same polarity.

Positive center pin is much more popular, but not "the standard".

The main reason that many items were center-pin-negative was that they had grounded metal housings. Charge jacks were all metal too, so it made since to go with negative on the outside of the plug. Now radios and everything else is mostly plastic so it has no advantage.

Another reason for "ground outside" was audio shielding. But we are dealing with battery charging, not signal.

I have been told, JR had the plug first, then other brands copied but reversed the polarity. When Futaba went to the center-pin-positve plug, they should have used a different size and type of plug. I don't know if this was true, but it sounds like it is.

I call it "JR's Bane."

Fuses do not protect against reverse polarity. Fuses protect against overcurrent and dead shorts. The radio should be sent to JR. I have found there are two diodes and a two regulators that are commonly blown on these radios.

Reverse current has been applied to all semiconductors attached to the ground plain, including the computer. This probably locked up the computer and drained the lithium battery.

This was my theory, then I got it confirmed when someone here in town fryed their radio and sent it in. He let me read the techie notes on his invoice.

It will be worth the money to fix it. The 652 is a very nice radio.

I finally traded mine off. I've got too many radios here!!! Time to fix some of my wrecked planes.
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