Mtx 3401

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i am fixing 2 of these amps simultaniously and i have run out of things to fix on one amp so i thought i could switch to this one.

this amp is the exact same amp as this thread

http://www.diyaudio.com/forums/showthread.php?s=&threadid=126125

with this amp i am getting 0v at the op amp and +- 2-3 volt at the regulators. the rail voltage is 2v and i cant see any obvious melt downs or burn marks. i checked the R106 location and surrounding components and everything measures fine.

where do i look now?
 
It sounds like the power supply is inoperative. What is the DC voltage on each of the legs of FET102 and FET104?

FET102
1.
2.
3.

FET104
1.
2.
3.

Don't plug this amp's preamp board into the other amp. If there's something wrong with the other amp that's causing the op-amps to fail, it will damage the op-amps on this preamp board also.
 
It sounds like the power supply you're using is set too low or is being dragged down by the amplifier. Does the voltage go higher (on the power supply) when you disconnect the amp?

The amp has low voltage protection (if I'm not mistaken) so it may not power up with only 8v.

Does the supply voltage remain at/near 12v without applying remote voltage to the amplifier?
 
it gives the exact symptoms with or without the resistor, the cooling fan comes on for a fraction of a second then it drops to 8v if i leave the full voltage applied for about 5 mins then the heatsink starts to get warm. i have 2 lights on the back of the amp labeled "thermal" and "short" neither of these light up.

i am measuring voltrage for the amp right at the terminals where you feed the power into the amp.
 
Pull the rectifiers (rec101, 102).

You'll need to keep them under the clamp so you can power up the amp without risk to the regulators. After pulling them, flip them, place them under the clamp (legs up) and tighten the clamp.

Then power up the amp through the resistor. If it powers up, the power supply components (including the transformer) are likely OK. There will be no rail or regulated voltage. The only point where you may find voltage (other than that supplied from the 12v supply), is where rec104 and rec105 are connected. That should be ~20v.
 
against everything i have read i pulled the clamps off and put power to the amp eek!!

it is quite obvious i am getting 4 of these rectifiers super hot.

FET 101,102,103 AND 104 all of them have the same part number 75339p. it only takes about 1-2 seconds for all 4 of them to get super hot. way too hot to touch.

should i flip all 4 of them upside down? or did i find the problem?

i promise i will never power it up with the heat sink unbolted ever again LOL
 
so now with the FET's reinstalled and the 2 REC's pulled out i am now getting 2V from my power supply

i slipped with the soldering iron and dislogged thie part in the picture. what is it?
 

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