FETs switching noise at the output

[starrlucky]

Hello forum!
I have Jensen 2000.1d D-class amp, which have output switching noise which is present at the output relatively to power source ground:
Blue: VS pin of IR2010S,
(Yellow) (+ terminal).

An externally hosted image should be here but it was not working when we last tested it.

And at the speaker terminals (between speaker ground and + terminal) I'm getting sine wave ~150khz and 4v rms, (it's without any signal at the input).
Is there any way that this could be normal? Amp is working when signal in, though.


I know that some D-class amps self-oscillating, but thing is that before it wasn't any of that noise or sine wave at the output.
Before that all the problem was with blown some of output fets and one gate diode, I've changed them, but After some time turns out that it was also transformers failure, because all irf3205 PSU fets and couple of output 640n's blew up. I've changed them. And now I see this picture.

Amplifier photos jensen amp — Yandex.Disk)

 

[barber02]

I haven’t worked on any Jensen Amps so I’m not familiar with them.

I would check the snubber networks around the transformers and inductors. Is the sine wave present with a load attached to the speaker terminals? What does it sound like in the speaker? Check for cracked solder joints, especially around larger components and jumpers.

Try twisting and wiggling the transformers and inductors to see if that changes anything with the noise.

Also, the brown glue that is used on that amp becomes conductive over time and with you heating things up and what not may have caused an unexpected electrical connection where that glue is concerned. I would try scraping that glue away that is touching the SMD components.

Double check your work for missed solder or solder bridges. Check for shorted caps and open resistors. Check the diodes and resistors at the transistors again in the power supply and output section.

Just my two cents,

David

 

[Perry Babin]

Do you possibly have a bad ground on the short ground clip for your probe?

I second the previous advice on the brown fixative if it's what it appears to be. If you set your scope probe to 10x, you can touch the probe to various points on the fixative and see signal and DC leakage through it.

 

[starrlucky]

Is the sine wave present with a load attached to the speaker terminals? What does it sound like in the speaker?

Yes, sine wave is present with the load. Also, if I apply test signal, I can see like my 50Hz sine wave kind of modulated with 150khz frequency.
Without signal it sounds just like white noize.

I've cleaned all the glue, checked almost all trough-hole caps for capacity.
It's the same, but now the amplifier sometimes won't start , it goes into protection (pins 1,3 on tl494 goes high). Wiggling didn't helped. Going to triple check everything (again).

Do you possibly have a bad ground on the short ground clip for your probe?

I tried to test it with other ground clips and another probe, same.

 

[Perry Babin]

150K isn't audible.

Are you using full range speakers or a proper subwoofer to determine if it's noisy?

 

[starrlucky]

150K isn't audible.

Are you using full range speakers or a proper subwoofer to determine if it's noisy?

No, I don't have an inductive load rn, so I'm using 2 Ohm resistor instead

 

[Perry Babin]

How does it sound like white noise if you're using a resistor?

 

[starrlucky]

How does it sound like white noise if you're using a resistor?

I've tried my computer speakers through resistor just to hear how it's souns like.

 

[Osvaldo de Banfield]

Some cheap Class D amplifiers don't use output filtering, so the RF maust be almost rai to rail, at the internal PSU levels.

In the other hand, the 4V is with the rigth load? Bad loading can cause the filter to operate in an no proper form.