Tannoy SFX 5.1 subwoofer with TDA7293 amplifier distorts

[mariadumitruiulian]

Hi everybody,

I have 2 Tannoy SFX5.1 subwoofers, one powered by a TDA7293 and the other one by a TDA7294.

Both subwoofers are "working", so sound is good at very low volume, but as soon as i rise up the volume more than 20% it starts to heavily distort .
I suspected the speakers at the beginning, and i tried to use other speaker that i know is good, but i get the same result.

Can a TDA IC be like semi-damaged, so it still kind-of-works, but distorts? (so changing it may solve the problem)...

Is there any other thing i should check? (i measured all the resistors and diodes in the circuit and all are fine, i cleaned the board of the glue(i read somewhere that this glue can became conductive over time), and i also visually inspected all the caps, and all are looking good, no leaks or deformation, i visually inspected the pre-amp area and everything looks fine)...

LE: I just checked it with an oscilloscope using a 40HZ signal, and the wave stays clean up to ~40% of the volume, then clips. Signal supplied from an Ipad.

Thanks for your help!

 

[MAAC0]

Have You checked the PSU rail voltages ?
It doesn't make sense testing components without checking the PSU first.


According to another board the IC should be a 7293 and not a 7294. Was it repaired before ? Check also Q151 and Q152 they say they get hot and discolored.

 

[mariadumitruiulian]

Hi,

yes i checked, i have the right voltage, ~ +-43V (if i remember well) measured yesterday.
2SC1815 and 2SA1015 were changed (that was initial issue).
I also changed the IC (on the TDA7293board) with a new chip, and behavior is identical.

I've seen a bunch of capacitors on the board... can any of those possible cause the issue? I am talking specially about those on the input and output...

Yesterday when i measured with oscilloscope i had 25V measured when playing 20Hz sine wave before amp would go to clip. Is that OK, or i should have more?

Thanks!