MTX Thunder 1501D

[caraudioguy2100]

I have an older version of this amp .

I’m going to to use the 3205’s in the power supply section .

Does anyone know the value of the 2 gate resistors R436,R435 ?

And wondering what outputs I can use in this since I can’t find the originals the originals are IRFB42N20D

 

[Perry Babin]

The gate resistors are 39.2 ohms.

The outputs are readily available.
IRFB42N20DPBF Infineon - MOSFETs - Distributors, Price Comparison, and Datasheets | Octopart component search

 

[caraudioguy2100]

Here is the drive signals for the power supply fets .

They are loaded with a 0.1uf cap scope set to 5us 5volts/div

Do these look fine or do I have an issue ?

 

[Perry Babin]

They look OK.

 

[caraudioguy2100]

Are these 2 transistors the correct transistors that go in these locations ?

And also what would cause D198 to burn ?

 

[Perry Babin]

D198 likely burned when the amp lost ground and tried to ground through the RCA shields.

Those FETs will work.

 

[caraudioguy2100]

I took the class D chip out and jumped pins 1 to 8 with a 1k resistor

When adjusting the gain the test speaker still has excessive movement and bounces back and fourth a lot .

Could this be from a bad gain pot ?

 

[Perry Babin]

Class D chip? U141 is a VCA (Voltage Controlled Amplifier). It has nothing to do with class D amplifiers.

Is the 1k resistor between D198 and D199 within tolerance?

Are you using a signal source with a grounded shield?

Are the RCA shields securely connected to the RCA jack frame?

Side note, leave the burned diode out of the circuit.

 

[caraudioguy2100]

My mistake calling it a class d chip .

The resistor measures within tolorance .

The rca jacks are securely connected to the frame

 

[Perry Babin]

What is the greatest voltage you read on the output pins of any of the op-amps in the preamp section?

Try with the black probe on the RCA shields and also on the primary ground.

 

[caraudioguy2100]

On pins 1,7 of the TLO72’s I get 0.14 volts

On pins 1,7 of the NE5532’s I get -14.75 volts

 

[Perry Babin]

Do all read the same using either ground?

Do you have ±supply on all of the op-amps?

 

[caraudioguy2100]

If I use main ground terminal I get 0.53 volts on pins 1,7 of the TL072’s

If I use rca ground I get 0 volts


If I use main ground on pins 1,7 of the NE5532’s I get 15.41 volts

If I use rca ground on pins 1,7 of the NE5532’s I get -14.86 volts

I have +- 16 volts on the supply pins for the opamps

 

[Perry Babin]

What is the DC voltage between the RCA shields and the primary ground?

 

[caraudioguy2100]

0.52 volts

I noticed the optocouplers have different voltages on the the voltages don’t match from 1 to the other is this normal or should I post the voltages ?

 

[Perry Babin]

How are you getting 30v of difference using two grounds that are 1/2v apart?

 

[caraudioguy2100]

My mistake if I use main ground on the NE5532 I get -14.85 volts

If I use rca ground I get -15.41 volts but only on 1 5532

All of the other opamps read the same no matter what ground I use the most voltage I get is 0.54 volts on pins 1,7 of all opamps .

I think the problem is with the optocouplers.

Here is the voltage on both of them

Pin 1:0.00
Pin 2:-0.06
Pin 3:0.00
Pin 4:0.00
Pin 5:0.01
Pin 6:6.87
Pin 7:7.04
Pin 8:19.26


Pin 1:0.00
Pin 2:0.00
Pin 3:0.00
Pin 4:0.00
Pin 5:-78.4
Pin 6:-70.4
Pin 7:-70.4
Pin 8:-58.0

 

[Perry Babin]

Does the amp produce audio?

What's the circuit board designation of the 5532 with -15v on its output?

 

[caraudioguy2100]

Yes the amp produces audio

The NE5532 with the 15 volts is this one in the pic

 

[Kevin2284]

What is d326?