Help me figure this problem

I have this table internet radio: Philips NP2900/12 and it's presenting this weird behavior.
It plays perfectly on low volume, but once i increase the volume to more than 20-30% the sound starts coughing - choking.

I first suspected the power supply (12V 3.5A external block), but testing with a different one (same specs) and even with a more powerful one (>5A) made no difference.

Can someone have a listen on this small video i recorded to show the problem and help me figure what's wrong.

Should i look on the amp circuit? It is a 4 speaker design with dual TPA3101D2, one driving the low freq. speakers, the other driving the tweeters.
Individual speakers are blown? (unlikely).
Or perhaps i should look for inner power circuit problems?


Edit: I opened the device and disconnected first the tweeters (to test it only with the low freq. speakers) and then the low freq. speakers (to test it only with the tweeters).
Same result.
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Could you please measure the DC impedance (resistance) of the 4 speakers?
Do you have access to an oscilloscope?

The resistance for the low freq. speakers are 8ohm nominal, ~7.5ohm measured.
The high freq. speakers are 12ohm nominal, ~12.3ohm measured.

And i wish i had one...

If possible return it for a refund, and get a radio that works.

Not an option. It's not new.

In your video there is a while device marked "Cosmote" behind the radio. Am I correct that is an ISP's router?

From that, and the sound in the video, the problem is radio frequency interference between the router's WiFi and the "radio". move them further apart, say 10 feet, and try it again.

It was there only for the video duration. i wanted to test it with a wired network instead of wifi.
It's place is in the next room 15 feet apart, where it started presenting the problem.
It's not interference.

I have a spare chinese tpa3116d2 board, i will try to open it and reroute the speaker amp stage input to that, and see.

I found the internal photos of the device (from fccid).
Page 10 is the speaker amplifier - power regulation board

Thanks for the replies guys...
I'd vote for inner power distribution issues - sounds like a rail is cutting out / drooping on load causing the amp to under-voltage cutout and then the systems recovers and repeats on the next signal peak.

That one has my vote too. Just to eliminate the obvious, i bypassed all supply plugs (3 in total !!!) and fed the 12v directly were it is supposed to go on the pcb. No change, so it must be later on.
Some mosfet switches power the speaker amps, and a dual switching regulator powers the rest of the electronics. The question now is finding it.

Another reason would be the mute and shutdown signals for the speaker amps from the control board (both used by looking at the pcb). They might have started to get noisy or floating.
Too many plugs interconnecting the boards...