Hifonics Brutus BRE2000.1D

Found this amp with a burned up trace under-side of one of the transformers at secondary ground. After repair, amp was able to power up and pass audio seemingly fine under small load so I re-mounted in the sync. I then tested at 2-ohm load, and after pulling about 10A of 13vDC current the sine-wave output turned into a saw and the amp went into protect. I can no longer get the amp to not protect, even with nothing connected. Its stuck in protect.

All FETs are measuring fine in circuit. The amp is back out of the sync and Im scratching my head a bit. Any thoughts?
 
I replaced both 1D/MBTA42 with MPSA42 units, carefully; and the amp powers up now every time.

It still has an issue though. With 2-ohm load, it'll pull out clean to about 14A draw just fine. A smidge over that and the output gets screwed and draws excessively.

Photos next
 
5v/Div. 100hz sine wave. Quite a bit of input voltage. You see the first photo the output gets badly distorted and pulls over current. The second photo is clean at ~13A.
 

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Once the amp gets to distort, I cant bring it back down by lowering the input voltage. I must power cycle the amp.
Twisting the inductors doesn't stop it nor does it prevent the issue from happening.
I replaced the usual suspect 072 OpAmp on the driver board - no change.

Where are the over-current transistors?
 
Ahhhh I solved this one. My Gophert 1620 limiting PS.... I love it, but sometimes it acts up when supplying amperage close to it's limit (20A). Its a 16v/20A adjustable, limiting supply which is pretty nice, but in this case was not providing this amp with enough current. Usually that doesn't happen... Maybe 10% of the time it acts funny with hungry or in-efficient amps. Thats what I get for using a chinese PS. Its nice enough though. Not many in-expensive bench top supplies can provide that much adjustable/limiting current. I do recommend this supply for functional repairing though. Usually an amp won't start to totally freak out until it draws about 18~19A from this supply.



I moved this Brutus to a 100A supply and it worked fine out to clipping at 2-ohm load pulling about 75A
 
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