HobbyKing.com New Products Flash Sale
Reply
Thread Tools
Old Mar 26, 2012, 07:30 PM
Psalms 23:4
Goshen, IN, USA
Joined Nov 2010
267 Posts
Question
Removing mosFETs to repair ESC

Is it possible to get a burned out ESC to work again by removing the burned out MOSFETs, and also removing the corresponding MOSFETs on the other two "lines"? Will I need to add resistors or something to make up for the burned out MOSFETs?

Here's the link ~ http://www.hobbyking.com/hobbyking/s...ontroller.html
miniprinter96 is offline Find More Posts by miniprinter96
Last edited by miniprinter96; Mar 26, 2012 at 07:41 PM.
Reply With Quote
Sign up now
to remove ads between posts
Old Mar 26, 2012, 07:53 PM
fmw
Registered User
fmw's Avatar
Joined Jul 2009
1,955 Posts
All that for $8.42?
fmw is offline Find More Posts by fmw
Reply With Quote
Old Mar 26, 2012, 07:58 PM
Psalms 23:4
Goshen, IN, USA
Joined Nov 2010
267 Posts
I have two more ESCs coming, but I might as well fix this one if I can. I have more time than money, so I want to save all I can. I have one other ESC, but it doesn't work will all my motors. I've tried changing the timing and start up speed, but I can't get it to work.
miniprinter96 is offline Find More Posts by miniprinter96
Reply With Quote
Old Mar 26, 2012, 08:01 PM
Jack
USA, ME, Ellsworth
Joined May 2008
17,111 Posts
The guys over on the DIY Electronics forum play around with that kind of work more there most do here. You might get better answers over there:

DIY Electronics forum - http://www.rcgroups.com/diy-electronics-199/

I personally doubt that the average person can do the surface mount soldering required. To say nothing or finding the parts and getting it engineered.

And, like fws says, it might not make sense considering the cost of a replacement...

Jack
jackerbes is offline Find More Posts by jackerbes
Reply With Quote
Old Mar 26, 2012, 08:09 PM
Psalms 23:4
Goshen, IN, USA
Joined Nov 2010
267 Posts
Would it be possible to just remove some of the MOSFETs without needing to solder on replacement MOSFETs? I have a good amount of soldering experience, so I'm fairly confident I can remove the MOSFETs without damaging the board. I know about the cost of buying replacement parts. I don't want to buy anything to fix it. I just want to know it I could remove the corresponding MOSFETs and have an operational ESC.
miniprinter96 is offline Find More Posts by miniprinter96
Reply With Quote
Old Mar 26, 2012, 08:18 PM
Jack
USA, ME, Ellsworth
Joined May 2008
17,111 Posts
I think you'd get the answer for that over there too as they build ESCs and stuff like that. I'm not much on electronics or theory.

My impression is that the number of MOSFETs (and their size of course) relates to the current that can be handled in a phase and that there is one field or array of MOSFETs for each of the three phases. So removing some of them would seem to diminish power levels at the least. I surely don't know if it could be done and let you still have a working ESC.

Good luck with it though!

Jack
jackerbes is offline Find More Posts by jackerbes
Reply With Quote
Old Mar 26, 2012, 08:26 PM
Psalms 23:4
Goshen, IN, USA
Joined Nov 2010
267 Posts
The ESC I have has 4 MOSFETs per phase, and 2 of them are burned out on one phase. So if I would remove 2 MOSFETs from each phase, would I get a 10A ESC? (as opposed to the original 20A)
miniprinter96 is offline Find More Posts by miniprinter96
Reply With Quote
Old Mar 26, 2012, 11:06 PM
Senile Member
Lnagel's Avatar
Moab, Utah, USA
Joined Apr 2003
6,232 Posts
The MOSFETs work as electronically controlled switches that open and close to allow current to flow through the appropriate motor windinings at the proper time. Without the MOSFETs in the circuit the switches a permanently open and no current will flow in the motor. The MOSFETs cannot be replaced by any other electronic component such as a resistor.

Larry
Lnagel is online now Find More Posts by Lnagel
Reply With Quote
Old Mar 27, 2012, 04:28 AM
We want... Information!
Bruce Abbott's Avatar
Hastings, New Zealand
Joined Jan 2001
5,190 Posts
Quote:
Originally Posted by miniprinter96 View Post
The ESC I have has 4 MOSFETs per phase, and 2 of them are burned out on one phase. So if I would remove 2 MOSFETs from each phase, would I get a 10A ESC? (as opposed to the original 20A)
Yes, depending on which FETs are burned. You must leave in at least two FETs per phase - one on the low side (connected to battery -) and one on the high side (connected to battery +).

When trying to fix an ESC with blown FETs, first I remove any that are obviously burnt, then I measure the rest with a multimeter (on 2k Ohms range) to make sure none are shorted between Source and Drain, Source and Gate, or Gate and Drain. After removing all blown FETs I then check that there are enough left to operate the ESC - if not then I tack new ones on as required. Finally I test the ESC on a regulated power supply with current limiting (set to 7V, 1A) and a small low Kv outrunner motor.

Once you have proved that the controller still works, you can then decide whether it's worth doing the job properly. Sometimes it is better to simply replace all the FETs, including those that still work. Otherwise you run the risk of subsequent failure, as the surviving FETs may have been weakened by the original burnout. You should also inspect all other components for bad solder joints and physical damage. If there is a fault in the control circuit then the ESC may continue to blow FETs intermittently.
Bruce Abbott is offline Find More Posts by Bruce Abbott
Reply With Quote
Old Mar 27, 2012, 07:36 AM
Psalms 23:4
Goshen, IN, USA
Joined Nov 2010
267 Posts
I don't want to replace any MOSFETs, I just want to remove the damaged ones on it now.

BTW, how do I check for shorts in the MOSFETs?
miniprinter96 is offline Find More Posts by miniprinter96
Reply With Quote
Old Mar 27, 2012, 07:46 AM
Psalms 23:4
Goshen, IN, USA
Joined Nov 2010
267 Posts
Here's a diagram of what I'm thinking. The filled in MOSFETs are the burned out ones. If I would remove the ones with the X, and move the lower right yellow MOSFET to replace the top left MOSFET, would it work? All the MOSFETs have the same number on them, so they should be interchangeable.
miniprinter96 is offline Find More Posts by miniprinter96
Reply With Quote
Old Mar 27, 2012, 08:14 AM
An itch?. Scratch build.
eflightray's Avatar
South Wales U.K.
Joined Mar 2003
13,613 Posts
Things may have changes some since I was last involved in PCB design. Back then, SMD's (Surface Mount Devices), were actually positioned and fixed to the PCB with adhesive during assembly, and then the assembly was wave soldered.

So actually getting dead SMD's off a board may not be easy, or at minimum, risk the copper tracks being damaged.

But then, nothing ventured, nothing gained, (or lost).
eflightray is online now Find More Posts by eflightray
Reply With Quote
Old Mar 27, 2012, 07:17 PM
We want... Information!
Bruce Abbott's Avatar
Hastings, New Zealand
Joined Jan 2001
5,190 Posts
Quote:
Originally Posted by miniprinter96 View Post
Here's a diagram of what I'm thinking. The filled in MOSFETs are the burned out ones. If I would remove the ones with the X, and move the lower right yellow MOSFET to replace the top left MOSFET, would it work? All the MOSFETs have the same number on them, so they should be interchangeable.
You can pinch a FET from one of the other phases, but there's no need to remove any others.

Quote:
BTW, how do I check for shorts in the MOSFETs?
Use a digital multimeter on its 2k Ohms range. Put the - probe onto the Source and the + probe onto the Drain. The reading should be higher than 1K Ohms. Now do the same between the the Gate (-) and Drain (+), and the Source (-) and Gate (+).

You may see some high resistance in this test due to other components on the board, but if the FET is shorted it will only show a few Ohms. Usually the short will be between the Source and Drain or Gate and Drain. If there is more than one FET in the bank then you may have to isolate the culprit by disconnecting one or more pins. Sometimes you can tell which one is bad by inspecting it - often there will be a crack in the top of the case and/or blobs of metal exuding from the sides.

To test a FET after it has been removed from the board, switch your multimeter to Diode Test. Put the - probe on the Source and the + probe on the Gate. This should show infinity Ohms, but will also turn the FET on. Now put the + probe on the Drain. It should show zero Ohms. Finally, momentarily short out the Gate to the Source. The Source-Drain measurement should now be infinity Ohms, proving that the FET has turned off.

Quote:
Back then, SMD's (Surface Mount Devices), were actually positioned and fixed to the PCB with adhesive during assembly, and then the assembly was wave soldered.
Wave soldering is not that popular now. In my experience the FETs are not normally glued on.

SO8 packages are fairly easy to remove, but the tracks are usually quite thick and soak up a lot of heat. Use a high power soldering iron with a large spade tip to unsolder all the pins on one side, or use a hot air gun to do the whole chip at once. When removing known bad FETs I simply cut through the pins on one side with a sharp knife, bend the chip up to break the other side off, then unsolder the bits of pin that are left on the board.
Bruce Abbott is offline Find More Posts by Bruce Abbott
Reply With Quote
Old Mar 27, 2012, 09:04 PM
Psalms 23:4
Goshen, IN, USA
Joined Nov 2010
267 Posts
I switched the MOSFETs, but I messed up some while removing them. I have 2 more on the way, so I guess I'll just need to be patient. I'll just chalk it down as experience. I think I could get one working if I ever need to do it in the future. oh well.

I did unsolder all the bad MOSFETs and the leads for the motor, and now I have a BEC. It's rather bulky, and it can't handle very many servos, but if I need a small BEC for a glider or something, I have what I need now.
miniprinter96 is offline Find More Posts by miniprinter96
Reply With Quote
Old Mar 27, 2012, 10:29 PM
Suspended Account
Joined Feb 2012
123 Posts
Quote:
Originally Posted by miniprinter96 View Post
Is it possible to get a burned out ESC to work again by removing the burned out MOSFETs, and also removing the corresponding MOSFETs on the other two "lines"? Will I need to add resistors or something to make up for the burned out MOSFETs?

Here's the link ~ http://www.hobbyking.com/hobbyking/s...ontroller.html
The only thing I can tell you is, Yes it is possible. It is not cost effective though. A replacement is 8 dollars and change, the MOSFETs to repair yours would probably cost more and SM devices are a pain to desolder without wrecking the board.

Just buy a new one.
buracho topspin is offline Find More Posts by buracho topspin
Reply With Quote  (Disabled)
Reply


Thread Tools

Similar Threads
Category Thread Thread Starter Forum Replies Last Post
I need help with Mosfet identification on my Jeti esc WickedFunRC Power Systems 35 Sep 24, 2013 03:13 PM
Ultimate ESC MOSFET Selection air Power Systems 22 May 20, 2008 09:59 AM
Home made ESC Mosfet problems Foxy Modeling Science 10 Jan 17, 2003 09:27 AM
ESC Mosfet Suggestions Neil McGrath Power Systems 10 Sep 19, 2002 12:54 AM