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Be Alert - shorted servo cost me a receiver and battery

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Be Alert - shorted servo cost me a receiver and battery

Old 07-04-2014, 08:12 PM
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gsmarino2000
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Default Be Alert - shorted servo cost me a receiver and battery

Guys, I was busy centering my servos before connecting linkages on a new plane. I was using a loose receiver with the battery directly plugged in. I had plugged in my second rudder servo, fiddled with the linkage and then noticed the servo wasn't moving when I moved the stick. By the time I saw the smoke it was too late. Servo is a dead short internally, melted down the connector inside the receiver, battery connector and battery wires. Melted the solder on a couple of pins in the receiver and started to melt the case. Burned my hand yanking out the battery wire, which is a good argument to use a switch when running this sort of tests..

Battery can be repaired by splicing on a new wire, but the $150 AS9310 receiver is toast. I probably have 100 Hitec servos ... I've had one or two die on me, but I've never had one shorted new out of the box like this. Thank goodness it wasn't a LiPo receiver battery.

Bottom line - don't get complacent even with the small stuff. Had I been paying more attention, I could have cut power before much collateral damage was done.

Greg
Old 07-06-2014, 08:32 AM
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Heard of it before. All brands. There is a scale guy who puts something in the servo harness that will prevent backflow dont remember what. Lost a big Stuka because of it that scared him to modify all his planes.
Old 07-06-2014, 03:01 PM
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Originally Posted by gsmarino2000 View Post
Guys, I was busy centering my servos before connecting linkages on a new plane. I was using a loose receiver with the battery directly plugged in. I had plugged in my second rudder servo, fiddled with the linkage and then noticed the servo wasn't moving when I moved the stick. By the time I saw the smoke it was too late. Servo is a dead short internally, melted down the connector inside the receiver, battery connector and battery wires. Melted the solder on a couple of pins in the receiver and started to melt the case. Burned my hand yanking out the battery wire, which is a good argument to use a switch when running this sort of tests..
Battery can be repaired by splicing on a new wire, but the $150 AS9310 receiver is toast. I probably have 100 Hitec servos ... I've had one or two die on me, but I've never had one shorted new out of the box like this. Thank goodness it wasn't a LiPo receiver battery.Bottom line - don't get complacent even with the small stuff. Had I been paying more attention, I could have cut power before much collateral damage was done.
Greg
Shortcuts often end up with unexpected outcomes.
Always use a switch harness when connecting a battery to Receiver or Servo Interface e.g. servo programmer.
Servo short likely when servo was stalled, especially a digital, and could have happened to any brand.
Providing a fuse for each servo is a bit of an overkill with modern equipment, especially if servo have been burnt in
on the bench and all hardware is installed mechanically correct, not reliant on "computer setup"

. Servo - 5 amp Fuse Leads to Protect Against Dead Short Melt-downs

. BURN IN - Aging of RC Transmitter, Receiver & Servo components

Much more information available under sub section:
"Battery Care, Performance & DIY Battery Packs."
and
"ESC & BEC - Setup to prevent majority of all RF Problems, Brownouts & Crashes"
"Glitches & Jitter in Receiver, Servo & ESC - Causes and Cures"
"Servo - Alterations, Calculators, Databases, Leads, Repairs, Convert to an ESC or winch & FAQ."
below
"Radio Systems, Accessories, Alterations and FAQ" at
Alan's Hobby, Model & RC FAQ Web Links

Alan T
Old 07-06-2014, 03:54 PM
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gsmarino2000
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Yes Alan, I remember someone warning me years ago when I was starting out to always use a switch harness. Unfortunately I got complacent after setting up a lot of planes with no issues. I assure you that I'm using a switch now. Also I tested the remaining servos (and the replacement) separately in advance. Regarding the servo being stalled as the root cause, not in this case. I had removed the servo arm (with linkage attached) so that I could center the servo. This was the first time power was applied to the servo and it had only it's own shaft; nothing to stall against.

I'll look into the links you mentioned.

Thanks,
Greg
Old 07-06-2014, 05:30 PM
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It might be worth sending the receiver to Radio South or the manufacturer before writing it off.
It's likely it lost a land and/or a regulator. A few minutes of checks by a skilled tech may reveal an inexpensive fix and you would be able to put it to use in a backup plane.
Old 07-07-2014, 06:06 PM
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grotto2,

The receiver actually still works, it's the melted solder and plastic supports that potentially resign it to the scrap pile. I could use it if I gave up 2 or 3 of the 9 channels and mapped the rudder to one of the aux channels. Very difficult if not impossible to get to the back of the board to re-solder the pins - it's blocked by the other 3 PCB's which are soldered together. I may call Horizon and see what they think.

Thanks,
Greg
Old 07-07-2014, 07:06 PM
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Yep, you're there and can see it. It sounds pretty rough.
I hate to see an expensive piece junked, but really it's not worth an airplane.
Old 07-08-2014, 06:24 AM
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Originally Posted by gsmarino2000 View Post
grotto2,

I may call Horizon and see what they think.

Thanks,
Greg
With Horizons reputation for customer service, you may wind up with a new receiver for little or no cost!!
Pete
Old 07-21-2014, 07:11 AM
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I had a similar event a few years back, also on the bench. The short was at the receiver and melted the pins off the PC board. I was still able to use the rx but the battery shorted out and blew a cell. Things can heat up quick.

Last edited by crossman; 07-21-2014 at 07:13 AM.

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