FETs switching noise at the output

starrlucky

Member
2020-02-19 1:27 pm
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).
[IMGDEAD]https://yadi.sk/i/KdhoN9am6K4VxQ[/IMGDEAD]

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)
 
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
 
Last edited:

starrlucky

Member
2020-02-19 1:27 pm
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 :cool:, 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.