The gate threshold voltage is where the MOSFET just starts to turn on (see the red boxed entry on the data sheet exerpts attached. The other plots show how the drain current varies with VGS and VDS.

View attachment 107892

Indeed it is, and will be fully open at around 8v, what that graph shows anyway. I didn't look as far as the graph. Sorry >.<.

 

I'm thinking that this resistor would be a decent replacement for the one that is broken... same resistance but by the size that the datasheet specifies it will be, it seems to be larger in diameter which indicates that it could be a higher wattage resistor which shouldn't matter/effect the electronics of the board, however i'm wondering if i should just bring it down to a 3W which from the datasheet specifications, measure 4mm (The same as the current one).

http://uk.farnell.com/panasonic-ele...j183/resistor-metal-oxide-18kohm-5/dp/2324614

 

They appear to be ~5w resistors, but if by daisy chain you mean in series, then you would not have had 300+ volts on the drain of the mosfet if one was open or disconnected..
Max.

 

I did indeed mean series, sorry for not stating that. Right okay, but i didn't touch this resistor and i know i didn't because that is the second thing i focus on not touching in case of the capacitor, for some reason, outputting power and shocking me while moving the board around. So i'm not too sure why or how this is broken.

The positive terminal of the large capacitor on the top of the board is connected to a diode and then connected to drain on that mosfet, so that is why we got a voltage on drain, maybe? The leading edge of those 3 series resistors is connected to a cap which looks like its another smoothing cap as its grounded but i can't see, without removing some components, if its connected to anything else.... I will get the hotair machine on in a bit and remove that cap to check for further connections.

 

A diode on the drain of the mosfet could be a BEMF component, if the anode connects to the drain then it is this.
Max.

 

It is exactly that.

This is the part, the markings are slightly different but it is a U4J diode: http://www.onsemi.com/pub_link/Collateral/MURA160T3-D.PDF

Just had a quick read on BEMF - Used to monitor the speed of the motor, right?

 

Hello,

The BEMF is short for Back Electro Magnetic Force.
Read this page for more info:
https://www.boundless.com/physics/t...-eddy-currents-and-magnetic-damping-571-8079/

Bertus

 

It is exactly that.
Just had a quick read on BEMF - Used to monitor the speed of the motor, right?

AKA A flyback diode (sometimes called a snubber diode, commutating diode, freewheeling diode, suppressor diode, suppression diode, clamp diode or catch
Max.

 

So knowing this in connected to the Drain, does this explain the voltage reading on the drain terminal even though the resistor is broken? So, would this resistor being broken still allow a voltage be shown on the drain but no voltage reaching the rest of the circuitry, including the gate terminal, or at least the device that is supposed to provide the voltage on the gate pin to activate the mosfet?

 

No the diode blocks any voltage in the +ve direction from the supply, IOW if you have voltage on the drain, then it has to come from the supply and shows the supply appears to be working., the diode conducts in the reverse if an opposite polarity voltage is load-generated.
Max.

 

This is where i have gotten up to.



From this, would i be right in saying that if the mosfet is not turned on then the negative of the motor out will not connect to gnd through the source of the mosfet, therefor the motor will not be on?

I haven't investigated the source enough yet but i think its connecting to ground.

 

Normally the drain will control the load and switch via the source to common (gnd).
Have you measured the resistance from source to the point you have marked GND?
(I'm not used to first drafts being that neat!).
Max.

 

I haven't tested the resistance from source to GND yet. If there is 0, or around 0, then it means its connected to ground, right? I use a continuity mode normally, but i'm guessing that you prefer to test for resistance in this instance?

Thanks for the comment about the neatness, i think i fell lucky on the placements of components, not needing to redo it in a second draft luckily.

 

Yes, It should read at or near zero ohms.
Max.

 

3Ohms

I don't like that, shouldn't it be <1Ohm for continuity?

 

I would trace the path back from the mosfet source pin to the to GND side of the supply.
Even if it is a current sense resistor in the source , it seems a bit high.
Typically <1ohm.
Max.

 

Source is has two traces from it;
- Connected to GND through a resistor marked 2R55.
- Routed through a 10k resistor to a MCU pin, then to GND through a small capacitor (Unmarked).

However, the 2R55 capacitor (pictured in the next post, had to take image on my phone) is reading 3Ohms. What % would you assume this resistor is? the 3Ohms is 17.6% outside of the 2.55Ohms labeled.

 

 

Assuming your meter is not that precise and also I would think the res is close enough for the circuit to work, It would appear to be a current sense resistor with the 10k is the reading take off for the MCU.
So it seems likely that it is something in the drive to the power mosfet?
Max.

 

Okay, so are we thinking that the gate pin is either not turning the mosfet on, or the mosfet is bad? The board is located in such an awkward place on the hoover so i'de rather probe around without having to have it connected to the 240VAC on the hoover to be honest. So, tomorrow i'm going to sketch out the gate connection and then see what could be bad on that line. Sounds like a worthwhile task?