Amp Power and Ground shorted, causes?

Yesterday as soon as i turned on my car all of my speakers started making weird noises that sounded like a techno song and then went quiet. I check my amps and the 6ch running these speaker was stuck on protect.
  1. I disconnected everything from the amp except the power/remote/ground = protect
  2. Just power and ground = protect
  3. Took out the ground lead and tried putting it back in = spark
  4. Used DMM to measure continuity = continuity detected between power and ground.
  5. Opened amp to check for any burned components = nothing everything looks clean
I connected the amp to my bench power supply set at 12V/2amps and no more protect BUT i believe its due to the low current supplied. The subwoofer amp and dsp are working just fine, I put in another 6ch amp in for now and everything is back to normal on my car.

This is an MMats Hifi-6150D which i sent in for repair 7 months ago for blown MOSFETs but this happened in a whole different car/system, mmats just gave me a whole different amp. I made a post about it here a while back but at the end i just sent it back because that amp did had a lot of issues.

I want to try fixing this one myself and save the $250 service.
 
Hello sure thing,

as per the voltage here:
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Some amp pictures:
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I did notice the circled outlets were all reading continuity.

IMG_20230817_121237.jpg

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Oh yes,

Those circled speaker terminals read continuity on my DMM, well the Pos/Neg pairs nearest to each other.

Additionally while taking the pictures, I tested the amp with no connection (open) between the remote and positive terminals and that made it go into protect right away like it did on the car. So technically the amp is "off" as it doesn't have a remote connection but the protect light turns on.

And yes i do have an oscilloscope, its an isolated kind in case that matters.
 
'Continuity' is meaningless. An incandescent lamp will read 'continuity' but isn't a direct short. Use actual resistance in the future.

Those terminals are directly connected to the secondary ground (and possibly the primary ground) in the amp.

Is the fuse blown?

Make/model of the scope? Do you know how to use it (many have one but don't know how to use them)?
 
Yeah youre right, I will use resistance on all terminals combinations i did prior later today. This amp doesnt have its own internal fuse so it relies on a fuse (60A) within my distribution box, which did not blow.

As per the oscilloscope, I have a Fluke 199C 200Mhz. Im not an advance user but definitely more than basic as I used them a lot back in my EE undergrad. I've been working as a software dev for a while so im a bit rusty on my electrical.
 
Sure thing, I just emailed them with a summary of the issue. And yes I have taken the board out of the metal casing to look under and everything looked just fine no burnt spots. I also have one of those little "TC1 Multi Function Component Tester" from amazon and maybe test each MOSFET with in, I think i should be fine testing in circuit with those particular components if memory serves me right.

* I also ran a little brush through the board and blasted it with air in case there was a rogue wire strand somewhere, but that didnt fixed the issue either unfortunately.
 
I took the amp board out again for another close view:
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I also did the following impedance measurements:
POS + NEG : 0 -->50k
POS + REM+ NEG: 0-->2M
REM + NEG: 1M
POS + REM: 1.42k
Circled speaker terminals: 0.1

I also took two random power MOSFETs out and tested good. Lastly, I noticed that the amp stays in protection with the POS and NEG connected but goes "normal" (blue) when I put 12v on REM.

**I also just measured the ESR on all electrolytic caps on the power side and the large group of medium-sized caps have an ESR of 5-8 milliohm and the two large caps measure at 35milliohms
 
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Back to my bench again,

Yeah, it seems it was my fault, my current leads are cheap thick ones. Im gonna order some better ones.
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Just tested again and it doesn't seem I have voltage on both negative and positive rails. Interesting that the amp is showing itself as "normal" (blue) though
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