Identifying a FET

[SyreKron]

Hi All. I'm working on an amplifier plate for a Boston Acoustics HPS12HO. She's a real "beauty" inside and I can't unsee what I've seen.

Anyway, the amplifier module appears to be class D and the output is stuck at one of the rails (+75V) which led me to a shorted high-side output FET.

It's a standard TO-220 with GDS on pins 1-3. The problem is that the markings have been ground off from the factory and I cannot identify it. I *think* I can see that the part number started with IR.

There are two other FETs in matching packages but their numbers are also sufficiently obliterated that I'm quite stuck.

I've got some IRF510's I could try but I'm really hoping someone has already identified these and could chime in.
*grasps at straws*

Thanks in advance,
SyreKron

 

[chermann]

Hi All. I'm working on an amplifier plate for a Boston Acoustics HPS12HO. She's a real "beauty" inside and I can't unsee what I've seen.

Anyway, the amplifier module appears to be class D and the output is stuck at one of the rails (+75V) which led me to a shorted high-side output FET.

It's a standard TO-220 with GDS on pins 1-3. The problem is that the markings have been ground off from the factory and I cannot identify it. I *think* I can see that the part number started with IR.

There are two other FETs in matching packages but their numbers are also sufficiently obliterated that I'm quite stuck.

I've got some IRF510's I could try but I'm really hoping someone has already identified these and could chime in.
*grasps at straws*

Thanks in advance,
SyreKron

pictures might help from your amp.
did you search for a schematic?


chris

 

[SyreKron]

Yes, I did search for a schematic but didn't find much.

I've posted images here: Boston HPS12HO Amplifier Module with mystery FETs - Album on Imgur


Thanks,
SyreKron

 

[JonSnell Electronic]

If the rail voltages add up to no more than 90volts, (+ - 45v) they will probably be OK. Don't forget to replace the IR type drive chip as that will be damaged.

 

[nigelwright7557]

Don't forget to replace the IR type drive chip as that will be damaged.

I definitely agree with this, if the IRs2092 is blown then simply replacing mosfet will just blow it again.
I designed and built a few 2092 based amps and every time one blew it took out the 2092 as well.

The commonly used mosfets with the irs2092 are IRFP4019 and irfb4227.
Depends on how much power you want.
If it has driver transistors or tc4420 then the mosfets will be irfb4227's.

 

[theAnonymous1]

Are you in the US? If yes, I can send you either some FDP2552 or FDP42AN15A0.

 

[SyreKron]

Good call on the MOSFET driver. The FET I removed is dead shorted between all three leads which means that the 75V rail got put on the output of whatever was driving the gate of the deceased FET. I'll trace the gate signal and see where it goes on that board.

There isn't much for ICs there. There is an 8-pin SOIC that also has its part number ground off. Hopefully one of the many discrete transistors on the board was being used as a gate driver as I'll have a better chance of IDing even the smaller discrete parts.

Yes, I am in the US (updated my profile). Thank you for the parts offer! Besides the IRF510s (100VDS) which are too small for this +/- 75V rail amp I have some leftovers from working on some JBL Eons that I think are higher voltage. Let me check my stash before shipping parts around the country.

Another data point: I measured the blocking diode's forward voltage on the other two FETs and got 0.77V for both of them.

Oh! I just found another thread which looks promising: DS-15 Class-D Modul with much Trouble and used in a lot of Models from Harman//JBL

 

[theAnonymous1]

Looks like it uses complimentary FETs, so the ones I offered won't work.

I found this...

Yet Another View - by wwenze: Boston Acoustics HPS 10HO subwoofer repair - Day 2

Quote of the very last comment on that page...

Transistor 1 is IRF3315
2 AND 3 IS IRF6215.RIGHT BEHIND THE FERRITE COIL IS TRANS 1

EDIT: I guess this might be the schematic?

http://www.diyaudio.com/forums/clas...rouble-lot-models-harman-jbl.html#post4641193

 

[SyreKron]

Transistor 1 is IRF3315
2 AND 3 IS IRF6215.RIGHT BEHIND THE FERRITE COIL IS TRANS 1

Quote of the very last comment on that page...

Those part numbers match the schematic posted on the thread I found. I'm planning to checkout the output filter and the gate drive circuits before replacing the FETs.

Thanks, all, for your help. I have hope of saving this from the trash heap now!