Heatbed MOSFET gets way too hot

Hello there! I own a Geeetech I3 Pro A with a GT2560 board. The MOSFET for the heatbed is getting way too hot on it and im looking for alternatives to fix it.

Earlier I had a Sanguino board. With that board I used to print ABS with the heatbed on 100-110C. The MOSFET never got to the point where you couldnt put your finger on it.

Now I have the GT2560 which is supposed to be better at cooling and has heatsinks on the MOSFETS. Im printing PLA with it now and have the heatbed at 60C. Within 5 seconds of powering the bed the MOSFET gets really hot and seems to be at the point of catching fire.

Here is a picture of the MOSFET(The heatsink is not attached for testing purposes): [i.imgur.com]

Here is what I have done so far:

- Checked the wires and connections.
- Meassured the voltage. Started out at 9,5V and ended up at 10,5V at 60C. Without load it is steady 12V.

Would a possible solution be to change out the MOSFET from the Sanguino board, or does anyone have any MOSFETs they reccomend?

Thanks for all help!

You could replace the MOSFET with a IRLB8743PBF
I've used them on the cheaper China RAMPS boards in the past before I found a quality RAMPS

Quote
SteveRoy
You could replace the MOSFET with a IRLB8743PBF
I've used them on the cheaper China RAMPS boards in the past before I found a quality RAMPS

Ordered a few so ill give it a shot. You think it will have a lower temp with that MOSFET? From the specs of the one I have and that one I would think the one currently on should have a lower temp, unless its defective.

You could check the 5V regulator onboard the GT2560. If it doesn't supply at least 4.7V your MOSFets won't switch fully ON. Thats where the big voltage drop comes from...
The other MOSFets fully switch at 3.3V, so they stay much cooler

Quote
o_lampe
You could check the 5V regulator onboard the GT2560. If it doesn't supply at least 4.7V your MOSFets won't switch fully ON. Thats where the big voltage drop comes from...
The other MOSFets fully switch at 3.3V, so they stay much cooler

Aha, that makes sense! Ill look into this. As im so impatient I think ill give it a go with the MOSFET I have on the Sanguino board. Ill post back how it works.

Update:

I did solder the MOSFET from the Sanguino board to the GT2560. I am crap at soldering and I struggled a bit to remove the MOSFETs. The small rings on the board itself came off due to the heat. Once I powered on the board again and turned the heatbed on nothing happend. After some meassuring it suddenly turned on, but now it won't turn off at all. And the MOSFET itself got way warmer than the previous one again. Not sure if this was due to bad connection when soldering or the MOSFET.

Ill look into repairing the board, or get a new one. Ill give it another shot once the MOSFET mentioned above here arrives.

Edited 1 time(s). Last edit at 08/02/2017 02:20PM by Jaran.

Did an attempt to fix the connections to the MOSFET as I managed to destroy the rings on the board you are supposed to solder it to.

Now it does not seem to power on the heatbed port at all.

Here is a picture of how it looks like(Please look past the horrible soldering....): [imgur.com]

Have I even soldered the MOSFET onto the right parts of the board? In my eyes that seemed like the correct places. Am I wrong?

Edited 1 time(s). Last edit at 08/02/2017 05:34PM by Jaran.

It looks like you have soldered the grid pin to ground, this is the right hand pin in your photo, it should be a small solder pad, not connected to the large mass.

Quote
obewan
It looks like you have soldered the grid pin to ground, this is the right hand pin in your photo, it should be a small solder pad, not connected to the large mass.

Thanks for the input! Can you spot the smaller pad on the picture? As far as I can see its only "the big field" around the left and right pins, and a thinner connection going to the hotbed.

Edit: Ah, I belive I can see the small pad on the other MOSFETs. Its pretty much just the circle around the leg, can't seem to see the actual copper road/wire going to it. I managed to destroy the rings on the board at first soldering attempt due to the heat. Any idea how I can get contact with where its supposed to be when I don't have the ring and can't see where its coming from? :/

Removed the soldering tin: [imgur.com]

Edited 2 time(s). Last edit at 08/03/2017 09:18AM by Jaran.

Hello

If you look at your own picture you will see two other MOSFETS above. your solder extends so far that it is shorting out the MOSFET.

The pad is a little rectangle using some solder wick remove about two thirds of the solder then try again.

I notcied. Take a look at my last post, I added a picture there with the solder removed. As you can see in the picture the little rectangle that I was supposed to solder it to got loose from the board due to the heat. I can't see any copper around it, so im not sure where to solder it now. Any tips?

See the Other Mosfet the pin has a black boarder completely around it,
The connection point is on the side of the board.



Allow me to the other side of the board

Quote
Roberts_Clif
See the Other Mosfet the pin has a black boarder completely around it,
The connection point is on the side of the board.

[attachment 96836 Image12.jpg]

Allow me to the other side of the board

Sorry for my lack of understanding. I see the pad im supposed to solder it to, but its completely gone. I can't say I can spot it on the other side of the board either.

Here is a picture of the other side: [i.imgur.com]

Ok, so the pad on the bottom of the board is not needed for tha gate leg of the FET, the track the gate pin solders to is located on the top (component side) layer.hopefully you still have enough of this track left to solder too.

Quote
obewan
Ok, so the pad on the bottom of the board is not needed for tha gate leg of the FET, the track the gate pin solders to is located on the top (component side) layer.hopefully you still have enough of this track left to solder too.

Uh, I think I might have damaged it too much on top too. Can you spot it on the picture in the post above?

Unfortunatly the white surface makes it very hard to see where the wanted track is,but i suspect it goes back behind the fet and under the heatsink.

Indeed, its hard to see. Ill dismount the heatsink and post back with what I find. Thanks for your help so far!

Edit: Here is the topside without the heatsink. Can't say I can see the track from here either [imgur.com]

Edited 2 time(s). Last edit at 08/05/2017 12:36PM by Jaran.

acording to the circuit, Q1 gate is connected to R32,
2 options . try scraping some of the white coating to see if you can uncover the broken track to connect too.
or maybe solder a wire between Q1 gate and R32. as in the pict.

Quote
obewan
acording to the circuit, Q1 gate is connected to R32,
2 options . try scraping some of the white coating to see if you can uncover the broken track to connect too.
or maybe solder a wire between Q1 gate and R32. as in the pict.

Will give this a shot tomorrow.

Did you get this information by looking at the picture or do you have a schema for the board? Any idea if it matters which side of the R32 component I have to go from?

Hi, from the schematic.
R2 is connected from Q1 gate to GND,

Quote
obewan
Hi, from the schematic.
R2 is connected from Q1 gate to GND,

'

Aha, did not know there was one released! Will give this a shot now.

Update: You guys are fantastic! Got it working now with wiring. Couldnt get the wire to stick that good with the soldering so the connections on the picture is pretty much just for testing. Will go buy some copper wire, assuming that will stick better. Guessing other than the fact that my board looks a bit broken the connections should still be safe enough to keep using it?

Atleast I achieved what I intended. The temperature is WAY lower now even without any fans turned on.

How the board looks: [i.imgur.com]

The temperature at reached temperature: [i.imgur.com]

Edited 2 time(s). Last edit at 08/06/2017 07:43AM by Jaran.

If you have a spare 1/4 watt resistor around, it might be neater to using a leg of the resistor between Q1 gate and R32, apply some solder to the wire 1st then solder it to the part,you will find the solder runs a lot smoother .


Glad your getting there

Good idea! Heading out tomorrow to buy a new soldering iron so could pick one up then. Thanks alot for the help!

Surprise, surprise.... As I was soldering on the MOSFET with the new wires the little component on R32 came off. The one with "104" marked on it. Any idea what this part is called and if it is possible to buy a larger one to solder on, or am I at the point of buying a new board?

Edit: Is that component simply a resistor? From a little research it seems that those 104 resistors are at 100k ohm. So I guess a regular resistor on 100k would do the trick, or does the actual look of the part matter?

Edited 2 time(s). Last edit at 08/07/2017 10:12AM by Jaran.

Fiddly lil buggers.
Yep its just a 100k ohm resistor.

Quote
obewan
Fiddly lil buggers.
Yep its just a 100k ohm resistor.

Cheers! Ill pick one up tomorrow and hopefully I can get it soldered to the board. Can't see where it goes from R32 on the schematic I found.

Got the resistor soldered on now, but the nothing happens while I try to turn the bed on. Can't say I understand the schematic fully. Do you know where the R32 component goes? Got a feeling I might have damaged the connection going to the R32 pins.

Here are a few pictures of how it looks like now: [imgur.com]

Update: Managed to open a garber schema for the board after some fiddling around. To me it looks like the pin is just connected to whatevers around that pin on R32 as its open in the schematic.

Here is how it looks: [imgur.com]

Guess I could just scrape off some of the top layers around it.

Update: I scraped off the layer next to it and reveleaed some copper. [imgur.com]

Would it be right to solder it to here or am I mistaken?

Edited 2 time(s). Last edit at 08/08/2017 02:23PM by Jaran.

Yes you can solder to any part of the copper you marked in red, you can solder the other end of the resistor direct to the leg of the FET gate leg if its easier.

Quote
obewan
Yes you can solder to any part of the copper you marked in red, you can solder the other end of the resistor direct to the leg of the FET gate leg if its easier.

I just tried it out at the spot I marked red, but it made no diffrence. The heatbed does still not turn on nor does the diode for the heatbed. Can't say I understand why

Edit: Ill start looking into how I can edit the firmware to use the heatport for extruder 2 for the heatbed. I don't have two extruders anyway. Once I get that sorted ill give the soldering another go

Edited 1 time(s). Last edit at 08/08/2017 07:49PM by Jaran.

You probably damaged the track that feeds power to the FET gate pin.
solder the 100k resistor from the gate leg too ground and allso scrape some of the feed track and conect a wire from the gate leg to the track, see attached pic.

Quote
obewan
You probably damaged the track that feeds power to the FET gate pin.
solder the 100k resistor from the gate leg too ground and allso scrape some of the feed track and conect a wire from the gate leg to the track, see attached pic.

And now its working again, thank you!