DJ Light sound to light mode fault

[ajp8868]

Hi All,

I'm trying to repair an issue on one of my DJ lights which appears to have randomly developed a fault. When it first happened, it was just continually reacting very, very fast which first lead me to believe the microphone was broken (it was rusty so I assumed). I replaced this but no help.

So that lead me to believe there was a short on one of these MOSFETs. I tested and sure enough one of them was shorted. I was probing while powered on (stupid I know) and I shorted the gate and source on one MOSFET which caused the light to completely stop reacting. So I replaced two identical MOSFETs, but still the same, no reaction.

I've measured each resistor and they all report the correct values, I've also checked each capacitor (out of circuit) and they seem fine. Lastly I replaced one of the T4 diodes as this tested as 0l in both directions out of circuit. Nothing has helped and it currently doesn't react at all.

If I place my finger on the board in different places it starts to react really fast again which I believe is because I'm conducting and may e shorting something.

Any help would be appreciated, thanks!

[ajp8868]

Can anyone help please? 

[DaJMasta]

Do you have an oscilloscope?  Shorting pins on a mosfet could mean its switched voltage could have been shoved down the gate line, which means the thing controlling it may be dead - my guess is a pin of that micro.  If that's the case, no signal should be present on the gate of the mosfet, and that would be why it's not reacting.


If there is signal there, then maybe it's something to do with the power of the mosfet or damage to what its switching.

[ajp8868]

Thanks for the replies. Sadly I don't have a scope yet, that will have to wait till I have a garage..

I've attached a couple of pictures of an identical light with a much cleaner board and circled the MOSFET I shorted.

If there was no signal being generated from the micro anymore, would it still react when I touch parts of the board, mainly above the MOSFET where the caps and diodes are..?