MTX Thunder 81001 component value/schematics


2020-09-22 3:26 pm
Hi there guys,

Does anybody know the value of R417 and R412?
Does someone has the schematics of this amp?
Also, what output fets are suitable for this amp?


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2020-09-22 3:26 pm
Thanks for the photo Perry.
No outputs came in this amp, could a 30NQ15T be correct?

I never worked on a MTX before, but I think I know how the basics of the output section works looking to the components.
FOD3120 were blown, as well as the NE5332 op-amps.
I changed the NE5532 and I did not yet install new FOD3120 optocouplers (first check if the drive signal is OK).

Both NE5532 heat up pretty good.
Input signal of the FOD1320 is not a nice wave and it's constantly but slowly changing waveform and frequency.
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You were both right, yes.
32 volts between Pin4 and Pin8 of the NE5532 closest to the FOD3120
The other NE5532 has 1.6v across Pin4 and Pin8.
And also, yes, only the NE5332 closest to the FOD3120 heat up the most. But the other heats up as well.

Perry, 100v rail caps
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The supplies of the FOD3120 read 18.35 and 20.50v. Also too high.
So all voltage supplies of the 4 IC's is faulty.

But what is feeding all 4 IC's? There is a 7805 regulator (5v), there are 2x PHP30nq15T (I assume it's on of those) and a IRF540. I saw in the datasheet the PHP30NQ15T is used for DC-DC converting. So it's probably one of those.
But because this is an N-channel component it must be regulated by a drive wave like a buck converter does (I assume). Couldn't it be a fault in the drive wave of the PHP30NQ15t?
Probing around does not directly conclude which regulator is feeding which IC. When probing around I probe the NE5332 on the 7805 regulator and the PHP30NQ15t on the other side of the board, the 7805 is obviously wrong.


2020-09-22 3:26 pm
Correct Bertje. C414 was not installed in the amp, as well as the output fets.
There is 60V across the pads of C414.
A new cap will fail instantly since the capacitor rating is 25V looking to perry's photo in post #2

Also C413 reads a not stable 27-30v across the pads. It looks like there is a 25v cap installed. Not good I suppose.

Is there anybody with schematics?


2020-09-22 3:26 pm
There is 30.2v NE5532's Pin4 and Pin8 close to the optocoupler and 1.6v across the other. Measuring on the oscilloscope measures a kind of unstable sawtooth shape wave on both pins.

NE5532 close to the optocouplers
Pin4: +- -62v (unstable)
Pin8: +- 30v (unstable)

Other NE5532
Pin4: 58v (unstable)
Pin8: 56v (unstable)


2020-09-22 3:26 pm
Ok, so, new readings.
The NE5532 PS pins are directly connected. The 25v 10uf caps seems to be the PS caps for the NE5532. They arr connected via a 0ohm fuse resistor. Strange readings from post #16

NE5532 closest to the optocoupler between Pin4 and Pin8 reads 30.45v now
Same reading to the other NE5532.
On the oscilloscope it reads different. Seems like both the multimeter and the oscilloscope can't get a steady DC value. Since the scope sees it as a 2-5v DC due tue the supply being glitchy, I see the multimeter as a better option in this case.

Readings across missing C414 is 58.5v
Across C413 is unstable +-30v

Since this is not a clean DC supply for the multimeter and scope and a kind of sawtooth wave I suppose this means that the regulation are not steady in frequency or duty cycle.
I checked with the oscilloscope, its not steady. Could this be true?
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