Anyone have knowledge of brushless power tools stuttering /'cogging'

[visor_down]

Hi all
Does anyone on here have any experience of brushless motors within power tools and the fault where they stutter or what I have learnt it's referred to as 'cogging'?

I have a brushless hammer drill 18v (cheapy worx), it has started doing this when you first pull the trigger, it stutters for a few seconds then will go to full speed, I'd prefer to repair it if possible, rather than replace, you can get a whole new trigger and electronic control unit, but cost makes it prohibitive.

Would anyone know what would cause this at a component level?
I've cleaned the trigger circuit board / contacts that slide on the board to no avail.
Was hoping I maybe able to just repair part of the electronics control within it.

Any advice appreciated

And yes I could just get a body only tool for a few bob but would rather repair it, it's otherwise as new.
These are the control electronics, I don't have a wiring diagram

 

[msh10]

Only issue I have had was the trigger, good soak with WD then switch cleaner (full of dust).

 

[DSR]

It will be a BLDC motor - three phase looking at the wires. First suspect would be one of the power MOSFETS. I'm assuming they are MOSFETS - would need a part number to be certain. Have a close look to see if they are all good and there are no scorch marks or big cracks. Whether you can replace them without doing too much damage is a different matter - you sometimes have to destroy the PCB and mountings to get them out and so have a hard time getting it back together satisfactorily

 

[visor_down]

It will be a BLDC motor - three phase looking at the wires. First suspect would be one of the power MOSFETS. I'm assuming they are MOSFETS - would need a part number to be certain. Have a close look to see if they are all good and there are no scorch marks or big cracks. Whether you can replace them without doing too much damage is a different matter - you sometimes have to destroy the PCB and mountings to get them out and so have a hard time getting it back together satisfactorily

Great thank you, that gives me a starter for 10, I'll take a look and update here

 

[visor_down]

It will be a BLDC motor - three phase looking at the wires. First suspect would be one of the power MOSFETS. I'm assuming they are MOSFETS - would need a part number to be certain. Have a close look to see if they are all good and there are no scorch marks or big cracks. Whether you can replace them without doing too much damage is a different matter - you sometimes have to destroy the PCB and mountings to get them out and so have a hard time getting it back together satisfactorily

I've taken a look and can't see anything obvious, my background is mechanical not electrical, so if by crack, we are talking hairline, that you can only see under magnifying glass, then might of missed it!

I've attached some photos if you have any further ideas to identify fault they would be gratefully accepted

 

[DSR]

You're doomed

Those three power MOSFETS are 'potted'. The manufacturers pour resin over the components to make sure you can't take them to pieces and so have to give them money to buy a new one stop them vibrating and increase the reliability.

Sometimes you can get the potting off but it is a lot of faffing about and never a quick process. You also generally damage the components and circuit board so badly in the process that you have to buy new anyway.

 

[visor_down]

You're doomed

Those three power MOSFETS are 'potted'. The manufacturers pour resin over the components to make sure you can't take them to pieces and so have to give them money to buy a new one stop them vibrating and increase the reliability.

Sometimes you can get the potting off but it is a lot of faffing about and never a quick process. You also generally damage the components and circuit board so badly in the process that you have to buy new anyway.

Oh well least I know now, thanks for info. Will make do with it until it finally gives up completely and then but something else