MOSFET FAILURE

Hi everyone, I have a new 1600w powered subwoofer but as I do second day sound test with only 30% volume it turned off suddenly while playing. I do not care about warranty because I know there must be something wrong in the design. I opened the circuitry and I found out blown out fuse and 4pcs of 40N60m2 mosfet shorted. As I look into the heat dissipation of the mosfet it is not bolted into the aluminum frame but rather fixed on the PCB. When I removed the PCB the mosfet is disengaged into the aluminum frame. Although there is a heatsink compound on each mosfet but I doubt that it may lose physical contact to the heatsink causing it to overheat and shorted the junction inside the mosfet. I ordered the parts but I will revised the heat dissipation of the mosfet. The original was a D2PAK and I ordered TO-247 so that I will fixed it bolted on the aluminum frame. New connection will be running 3 wires for each mosfet mounted on the aluminum frame soldered to the PCB . Could somebody comment if what I will do is correct and if not what other remedies I will do. I'm from Philippines and I will solicit your expertise on these matter since I'm living in a poor country.

Sounds like you are on the right path.

Two thoughts though.

1) Was the original MosFet fully overmolded? If it was, it would be isolated from the aluminum frame. You will need some insulators for the TO-247.

2) I found it odd that a subwoofer amplifier would use a 600V MosFet.

I don’t have doubt on the design because it’s a Yamaha DXS18-XLF but it needs refinement since it is their latest product

Not very wise to modify a class-D high-power amplifier. Every part must be well within design specs. High voltage fets could mean high rail voltage. My DIY speakers run on 2*50volt, bridge (100volt peak/peak on the woofer). Are you sure it's the amp parts, and not the supply (which uses 600volt mosfets). Supply fets can pop with 'dirty' mains power. Leo..

It is not the power amp mosfet but rather the power supply component since it is a separate board from the amplifier

Then put it back EXACTLY as it was before, with the SAME parts. You might have to invest in a power surge protector (plugs into the wall socket). Leo..

It is still the same mosfet but a different package I could hardly remove the old one and solder the same type

kidong: It is still the same mosfet but a different package I could hardly remove the old one and solder the same type

If you can't (don't have a hot-air soldering station), then you shouldn't be doing this. Leo..

Sir the D2PAk has extended metal soldered at the tip and it is close to other parts that's why I decided to isolate and fix on aluminum frame I already ordered TO-247 but what would be the difference if I will prefer for that scheme

How do you think they have soldered the D2PAK mosfets in the factory. They are easilly replaced with a hot air soldering tool, set to 220 degrees C.

I have worked for almost half a century in consumer audio, and the worst things to fix were the items that already had been 'fixed' by the customers. Bring it to someone who knows what he/she is doing. Leo..

Ok i'll appreciate your ideas but I want to explore in my own I already broke the warranty so I have no choice but to repair it myself it's a challenge for myself I been doing electronics repair before 20yrs ago and I became a Relay Engineer for almost 20yrs now so it is not a difficult task for me

If it's your profession, then you should buy a hot air wand and solder paste. They're not that expensive on ebay. All modern electronics is using surface mounted parts nowadays. A hot air wand is almost a more important tool to have than a soldering iron. Replacing SMD parts with through-hole parts could become ugly and dangerous. Good luck. Leo..