Mighty Mule FM500 blew up green circuit board by reversing battery

What generally blows up when a Mighty Mule gate opener battery is hooked up in reverse by accident?

I blew up something on the green Mighty Mule FM500 GTO gate opener circuit board. Now I have a constant alarm and the gate won't operate.

I have basic soldering skills. I'm pretty sure the same stuff blows up each time the battery contacts are accidentally reversed.

If you've ever fixed the blown Mighty Mule circuit board, can you tell me which component is the one that fails?

Reply to
Joseph Donner
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Post a schematic.

There might be a protection diode for wrong polarity. A simple parallel diode protection only protects briefly then the diode blows. A parallel diode with a series thermistor on the power (or fuse) is better, the thermistor acts like a blown fuse when it gets hot, then conducts again when cool. Sometimes a bridge rectifier or series diodes are used. Start testing parts from the battery terminals going deeper. Check any thermistors, fuses or diodes first. Hopefully something in the protection circuit blew and no current got to the functional circuit.

Reply to
RickH

I asked GTO Technical Support but they said they don't have schematics for the green Mighty Mule FM500 circuit board.

Searching the net, I find this great set of GTO circuit board manuals:

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I was hopeful when I saw what appeared to be the perfect link there: "FM500 Green Board"

However, when I click on that link, unfortunately, I can't read the PDF:

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Do you have a better PDF to read this Mighty Mule FM500 (green) circuit board schematic?

Reply to
Joseph Donner

What? You don't have PDF reader? It's free from Adobe.

Reply to
Tony Hwang

I got curious and tried the link. It looks like one hell of a big file, it was downloading for over a minute when I got scared that it may be a virus and stopped it.

Reply to
Tony

I couldn't find a way to read the PDF schematic and nobody knew where there was a schematic for the GTO gate opener (green) was so I had to give up on trying to fix it after I accidentally reversed the 12v battery (you'd think they would have protection circuitry built in for that).

So to give an update to my friends out there ... I just now ordered the Sears Item #00977051000 Mighty Mule FM500 Model R4211 Replacement Control Board (blue) for 322 dollars ($280 + $28 tax + $14 shipping).

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Thanks for your help. I also picked up a few more of the gadgets that go with the gates, so it will be interesting to put it all together when it arrives.

They say to bury the 16 gauge multi-stranded two-wire low voltage wire. I was thinking of putting a PVC conduit in since animals chewing on the wires started this whole mess in the first place.

Do you know what size PVC conduit & how deep to bury low-voltage wires in?

Reply to
Joseph Donner

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Did you notice the rebate offer on that site?

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First, check your local codes.

If your existing wire is type UF intended for direct burial, many jurisdictions do not allow the use of such cable within a conduit. For use within a conduit, type TW (THWN or THHN/THWN) wire is usually required.

The last time I checked, 1/2" PVC conduit can house up to five 12- gauge wires or six 14-gauge wires. Larger conduit makes it easier to pull the wires and add new ones later.

Remember to get a spool of nylon string when you get the conduit.

Good luck.

Reply to
RosemontCrest

How many wires? Usually 1/2" PVC works OK. Deep: about 16 inches, if low voltage circuit in conduit. Deeper if possible if no conduit.

Reply to
PeterD

PeterD wrote in news: snipped-for-privacy@4ax.com:

you want to bury pipes and wiring below the frost line in your area. Otherwise ground heave will break them.

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Jim Yanik
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Reply to
Jim Yanik

Yikes. I will call them back to get the rebate! Thanks.

Interesting. I didn't realize the wire had to be different if it went inside the conduit. Now it makes a bigger difference which way I go, conduit or not.

Is this for pulling the wire through the conduit?

Reply to
Joseph Donner

I will probably put two sets of double-stranded 16AWG wire in the conduit. One set will be for the 18VAC power and the other set for the intercom.

16 inches seems pretty deep. I was thinking more like half that (there is no frost here).
Reply to
Joseph Donner

Thanks for checking. I thought it was just me. It would be nice to find a schematic for the Mighty Mule FM500 circuit board (green).

Reply to
Joseph Donner

Yes. When you install the conduit, you can either include the string and wires when you glue together the conduit, or you can just include the string. If the latter, when pulling the wires, add another length of string to enable pulling additional wire in the future. Always keep a length of string in the conduit.

Reply to
RosemontCrest

Leave it in the conduit, when you pull your wires through. Then at some point in the future when you need another wire in there (it always happens) it is easier to pull that new wire in the conduit.

Reply to
PeterD

YOu want it below where any landscaping/gardening/maintenance is likely to hit it. That's the 16 inches.

Reply to
PeterD

Again, pull a new length of string when adding new wires. Always keep a length of string in the conduit.

Reply to
RosemontCrest

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Exactly. It's not just the concern of frost damage. I would bury it at least 24".

Reply to
RosemontCrest

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