# MMats HiFi 6150d repair journey



## Andre2142 (Feb 5, 2021)

Hey all so I took a gamble a bought an MMats HiFi 6150d that was just stuck in protection. I have SMD soldering and development experience but this is my first time working on an amplifier so far I've been getting some help but i figured I ask here too. Well I opened it up and noticed this, definitely blew but the damage seems to be on the FETs mostly, I want to try and fix this myself as MMats charges $250 to get this done, but if i must I will.

Clearly, a MOSFET died









I took out the clamps and noticed that 80% of the MOSFETS cracked or burnt on this rank of fets alone, all the other MOSFETS around the amp seem fine.









I cleaned out the smoke residue and noticed two resistors blew, I checked the diodes and they test out fine still. I also noticed the temperature sensor (?) on the upper left has its leads burnt, but I think that is due to the MOSFET nearby producing heat.









So now to gather parts, as I understand when a MOSFET gives out, it takes its driver IC with it but I don't know which one is it

















































*Now to some quick testing:*
So I used ceramic caps betweenGate and Source on the MOSFET holes. I could've used 103 or 104, so I will go with 104.










Removed all that carnage, the labels are so faded that even then its hard to make out the labels.










Ok, i think the IC has gone kaput...

I placed the capacitor between 1&3. (Also the power supply used is a Regulated PSU rated at 12V30A)










Here you can see where I place the main lead









And the GND










I also tested all of the gate resistors, and they were all measuring at 24.8 Ohm +/- 1%, I also tested all pads for continuity and no continuity was found between all 3 pads for all MOSFETs holes

Oscilloscope settings:




















Tested without a capacitor first and no square wave signal was detected.









Weird signal...










Tested *with* the capacitor shown in my previous picture and the signal was not as expected:


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## Andre2142 (Feb 5, 2021)

Googling around I found suggestions to test the SG3525 chip. So I just went ahead and tested the output terminals on the SG3525, as per the picture below i tested all 3 (1,2,3) that seemed to be output.

Here is the pinout i got from its datasheet:









I also took it out and cleaned with some Dexoit to be sure everything was connecting well.










Pin 4 "OSC, Output" gave me this wave with the capacitor *on*:



















Pin 11 "Output A" and Pin 14 "Output B" both gave me:










Pin 4 "OSC, Output" gave me this wave with the capacitor *off*:
-Weird, i was expecting a square wave.










Then I read a suggestion to disconnect pin 10 and test again, and what do you know..there's signal:
Moved pin 10 to the side:









Went ahead and tested with capacitor: *off*
Pin 4









Pin 11&14 now shows a signal










capacitor: *on*
Pin 4









Pin 14









Pin 11:










although the signal is present it doesn't seem to change with or without a load. So now im stumped here.....



Additional quesitons Questions:

What should I do next?
Any other IC I should test?
What resistors should I use? -markings have been burned out, and the only clue I have is a nearby one that is the same physical size with margins "10RD" (or 10R0), every other resistor is smaller in physical size.
What driver IC can I use?
Anything else I'm missing before I go out and buy parts?
Thanks!


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## oabeieo (Feb 22, 2015)

Andre2142 said:


> Googling around I found suggestions to test the SG3525 chip. So I just went ahead and tested the output terminals on the SG3525, as per the picture below i tested all 3 (1,2,3) that seemed to be output.
> 
> Here is the pinout i got from its datasheet:
> 
> ...



Obviously clean the board after aqueous flux or use a good no clean , looks solid there 


As for parts , man get with Maats and find out 

Or get a donor amp


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