Fonestar AS-24U

[sargantana]

Hi all, I'm trying to repair a cheap Fonestar AS-24U a friend has given me. I'm doing this only for learning purposes, so I already know it's a cheap unit and probably wont worth the effort. I don't have any other speaker to test the unit with but a car one, it's a 4 Ohm 150W JBL, for testing purposes I suppose I'ts ok.
The unit powers on normally and I'm able to playback MP3 from the SD card but the sound is only good at minimum volume (barely audible), if I push just a little the volume it crackles and pops louder than the music itself.
I'm a complete newbie (just know some basics) and didn't know from where to start, so I started from the beginning, the transformer that powers on the unit.
In the board where the transformer is plugged it says that the transformer should give gnd, 18v ac, 18v ac, 9v ac and 9v ac, tested with the multimeter with the amp powerred on it reads 19v 19v 1v 6,5v. Could be that the problem?
If that's the problem I supose the coil of the transformer is not serviceable and my journey ends here

Thanks in advance!!

[sam_sam_sam]

Re: Fonestar AS-24U

Could you please post a photo of the power supply board where the transformer wires hook up to

[R_J]

Re: Fonestar AS-24U

There are only two windings from the transformer, one is 19 volt center tapped 19ac-ground-19ac the other is just 9vac across the two points, it is not center tapped
The 19 center tapped ac will be rectified and lead to the large capacitors to provide + and - 24 vdc for the output ic
The 9vac is for another low voltage supply likely 12v dc

Look up the number for the amp ic TDA7265 and download the pdf, that should give you an idea of what dc voltages to have on the pins.

[sargantana]

Re: Fonestar AS-24U

Could you please post a photo of the power supply board where the transformer wires hook up to

Is the left bottom corner one in the first photo

[sargantana]

Re: Fonestar AS-24U

There are only two windings from the transformer, one is 19 volt center tapped 19ac-ground-19ac the other is just 9vac across the two points, it is not center tapped
The 19 center tapped ac will be rectified and lead to the large capacitors to provide + and - 24 vdc for the output ic
The 9vac is for another low voltage supply likely 12v dc

Look up the number for the amp ic TDA7265 and download the pdf, that should give you an idea of what dc voltages to have on the pins.

I measured between the two 9vac pins and in fact it reads 8,2v, so I assume now that the transformer is fine

Now I've downloaded the datasheet for the TDA7265. this nigth I'll try to check the dc voltages on the chip. Thanks!

[R_J]

Re: Fonestar AS-24U

That 8.2v ac gets rectified & filtered and likely supplies IC2 the 7805 5 volt regulator ic. Be careful when you check the ic that you don't short any pins. I doubt you will find a schematic so good clear high quality, straight on pictures of the trace side would help.
You may want to clean that brown glue crap from between the large caps and from that ribbon connector

[sargantana]

Re: Fonestar AS-24U

That 8.2v ac gets rectified & filtered and likely supplies IC2 the 7805 5 volt regulator ic. Be careful when you check the ic that you don't short any pins. I doubt you will find a schematic so good clear high quality, straight on pictures of the trace side would help.
You may want to clean that brown glue crap from between the large caps and from that ribbon connector

On the 7805 i get 9.65v dc between groun and input and 4.93v dc between ground ant output, so that one seems ok.
I didn't found the full board schematic for Fonestar AS-24U, but in the board it says E-SA9M, searched that and i found a pdf, it seems to be in hungarian, and I think is not the same board I have.
So I downloaded the TDA7265 pdf, by now tried to check the +Vs and GND pins and it's 24.8v dc.
To go further I suppose that have to test voltages in IN+ TO GND pins and OUT+ to GND pins while the amp is playing back audio isn't it?

[sargantana]

Re: Fonestar AS-24U

I've got no luck testing the amp ic, not really sure of what I'm doing anyway, here is a video with the problem, could it be bad caps?
I'll try to make a capacitor tester with an Arduino and verify them, my multimeter is only able to check nF capacitors.

[sargantana]

Re: Fonestar AS-24U

Found a better way to put the video
https://streamable.com/zl82g

[R_J]

Re: Fonestar AS-24U

Does it happen in both channels? maybe try a better speaker if you can, How does it sound without the tweeter attached ? use the larger speaker to test each channel seperate.

[sargantana]

Re: Fonestar AS-24U

Does it happen in both channels? maybe try a better speaker if you can, How does it sound without the tweeter attached ? use the larger speaker to test each channel seperate.

Wow, now I feel stupid and happy at the same time. I've separated the channels, and it's fine!!
They gave the amp with both channels junctioned and never thougth that could be a problem (As I said in the first post I'm really a newbie).

Thanks for all R_J.

[R_J]

Re: Fonestar AS-24U

Good to here its working.