Odd part designation help

[sr1200]

Have a mackie mixer that wound up in the shop that someone had spilled a drink on at a gig. After cleaning the board thoroughly, i set sights on the power supply. A switching supply with a few parts I had never seen. First was the fuse that looked more like a wima cap. Replaced that only for the supply to zap the replacement. Looking around i found a TO220F type chip and it has 2 designations on it. On the top it reads 2N48AA and below FQPF3N80C. I was able to find the second designation (mosfet 800v N-channel) but the first part has me scratching my head. From what it looks like to me, that part seems to be connected to the phantom rail (unless i traced it wrong). The 48 in the top designation makes me think there might be a 48v diode integrated somehow. Since the original is now internally shorted, i have no way to test this. Anyone familiar with this part and can i just swap the 3N80C for it. I can't find anything besides a regular diode with the top designation, certainly nothing with a TO220F package. Or could this be a mackie proprietary part for their PS... I can buy a new power supply for the unit for $100... just trying to save the guy some money on the repair if it can be done with parts for less. Thanks.

 

[Khron]

The "48" there is simply a coincidence. If it's an 800V MOSFET, that'll definitely be the main switching element in the primary side of the power supply (most likely a flyback design).

That entire top row of markings is a date-and-factory code; "48" very likely stands for week 38 of whatever year either "2N" or "AA" stands for.

You should be able to substitute that with just about any other 3A 7-800V MOSFET. Maybe you'll want to make sure the replacement's input capacitance is within the ballpark of the original.

But then again, if the MOSFET blew, you'll also want to check the current-sense resistor connected to its source pin, as well as the clamping diode(s) connected to its drain. And whatever controller is used to drive the MOSFET, it's not at all impossible that ended up getting damaged as well.

The rule of thumb is, not replacing a fuse before you've determined why it blew in the first place (by checking the "bigger" things downstream of it).

You could have also mentioned WHAT "mackie mixer" this might be. Mackie / LOUD technologies are kind enough to have a pretty comprehensive database of schematics, freely available on their support page...

 

[sr1200]

it is a LOUD board. the mixer is a proFX12. Thanks for the info. I was expecting the fuse to blow again, but decided to try it anyway on the off chance that whatever shorted on the top of the board just caused too much draw from liquid contact. NOTHING on the board looked cooked (except the solder pads on the fuse) so there wasn't anything "obvious". The resistor coming off the mosfet is reading properly and the diodes seem to be fine as well. Theres a tiny little cap thats thermally coupled to the heat sink of the mosfet. Haven't seen that before either. Do you have a link to the DB of schematics?

 

[sr1200]

https://mackie.com/en/support/schematics?folderID=11349
I found this, but theres no new-er schematics in there.

 

[ccaudle]

a tiny little cap thats thermally coupled to the heat sink of the mosfet

Probably a thermistor for temperature sensing.

 

[Khron]

https://mackie.com/en/support/schematics?folderID=11349
I found this, but theres no new-er schematics in there.

https://elektrotanya.com/mackie_profx12_sch.pdf/download.html
No power supply schematics though. Unless it happens to be branded Mackie / LOUD on the circuit board, good chance it's some off-the-shelf unit.

 

[sr1200]

its branded loud. Just too new. Its current production.

 

[Khron]

its branded loud. Just too new. Its current production.

But then again, if the MOSFET blew, you'll also want to check the current-sense resistor connected to its source pin, as well as the clamping diode(s) connected to its drain. And whatever controller is used to drive the MOSFET, it's not at all impossible that ended up getting damaged as well.

The rule of thumb is, not replacing a fuse before you've determined why it blew in the first place (by checking the "bigger" things downstream of it).

Some photos of the thing might not hurt, y'know...

 

[sr1200]

 

[sr1200]

Bottom

 

[sr1200]

Bump if anyone has thoughts. Posted pics above.

 

[Khron]

Fine, ignore my thoughts then

 

[Disco Volante]

Upon close inspection what looks like a blue tantalum is indeed marked NT1 on the PCB... Otherwise, +1 to the musings of Khron...
Regards,

 

[sr1200]

So i replaced the FQPF3N80C and the fuse, and it works perfectly now.