MTX 1501D problem power supply

[yoppi]

Hey there

I'm new to the forum. I hope to help and contribute as much as possible .

They have an amplifier MTX 1501D , which would have replaced the transistors of the power supply by IRF1010E , since according to the datasheet , are of better performance than the 75339p . IRFB42N20D are disconnected.
The amplifier turns on well but the coil of the power supply is noisy , and LED 399 is on, the LED 238 is off.
U1540 voltage is approximately 75V .

Why the power supply coil sounds ?

Thanks and Regards.

 

[Perry Babin]

The power supplies in these amps were noisy. It may not indicate that there is a problem.

 

[yoppi]

Good night from Spain

Thank you very much for the answer, Perry Babin . I have ridden IRF1010E transistors in the power supply.
Ride the output transistors and will comment .

Greetings and thanks

 

[yoppi]

Good night guys.

Mount the output transistors. They reach about 75 volts, but no audio output. I checked with oscilloscope and the wave is flat, 0V.
I checked RCA, part of pre-amplification and get no error.
Why it may be due?

Regards.

 

[Perry Babin]

Where did you read the 75v?

Are you getting rail-rail voltage swing on the output transistors and into the output filter inductors?

 

[yoppi]

Hi

Tensions are output transistors.

Fet: 255, 256, 257, 258. Gate: 75V, Drain: 0V, Source: 75V
Fet: 245, 246, 247, 248. Gate: 0V, Drain: 75V, Source: 0V
FET 260, Gate: 58V, Drain: 0V Source: 58V
FET 327, Gate: 75V, Drain: 75V, Source: 75V

Regards.

 

[Perry Babin]

It appears that you don't have any negative rail voltage.

 

[yoppi]

Sorry, it is my fault

Tensions are output transistors.

Fet: 255, 256, 257, 258. Gate: -75V, Drain: 0V, Source: -75V
Fet: 245, 246, 247, 248. Gate: 0V, Drain: +75V, Source: 0V
FET 260, Gate: -58V, Drain: 0V Source: -58V
FET 327, Gate: -75V, Drain: +75V, Source: -75V

A3120 voltage obtained:

Side capacitors 1000UF: legs 1-4: 0V - leg 8: -58,4v, leg 7: -75v, leg 6: -75v leg 5: -75v
IC capacitors 3300uf side:
legs 1-4: 0v - leg 8: + 0.1v, leg 7: 0V, leg 6: 0V, leg 5: 0V

Regards.

 

[Perry Babin]

If FET327 is the one in the center of the board, it has nothing to do with the audio.

To measure the supply voltage on the 3120s, you need to place the black probe on pin 5 and the red probe on pin 8. Do this for each 3120.

 

[yoppi]

Hi

A3120 voltage obtained at pin 8:

A3120 side capacitor 1000uF: 19,7V
A3120 side capacitor 3300uf: 1,28v

Regards.

 

[Perry Babin]

Did you measure each one with black on 5 and red on 8?

 

[yoppi]

Yes, this measured with black lead of the multimeter to pin 5 and
the red lead on the red pin 8

 

[Perry Babin]

Do you have both positive and negative power supply voltage (~±18v) on the op-amps in the preamp section?

Are the two 0.22 ohm SMD resistors near FET471 within tolerance?

 

[yoppi]

Hi

The resistors smd are replaced.
That 2155, voltage in the leg 7: 19,6V. In the remaining legs 0,55V.

Regards.

 

[Perry Babin]

Do you now have proper voltage on the opto-coupler that previously had less than 2v?

 

[yoppi]

not as usual

 

[Perry Babin]

I don't understand.

 

[yoppi]

Sorry, same voltage in the octo-coupler, 1,28v in the leg 8

 

[Perry Babin]

Do you have positive and negative voltage on the power supply pins of the op-amps in the preamp section?

U141 isn't an op-amp.

 

[yoppi]

It refers to the IC tl072c and NE5532?