Repair broken Logitech z5500 sub

[a.ekholm]

Hi!
I'm trying to repair a Logitech z5500 subwoofer. When it was connected to power the subwoofer outputted a LOUD hum. It also smelled burnt.
The smell located me to one of the tda7294 chips. I added some pictures of the board with closups on two burnt tda7294 chips, and also other parts.

It feels like changing the two tda-chips will not fix the root problem. Where should I look for the case? Voltage regulators that are shorted?

How should I proceed with trying to repair?
As it behaves now I am not comfortable to measure with it powers on (when smoke came from the tda-chips.)

1. Should I remove the chip and power it up?
2. Could a variac help me, and how?
3. Buy new chips (and spares) and replace and see if that helps? But when two chips are are burnt it seams like other issues exists? Likely they will also be burnt.
4.?

Thanks! /Andreas

I'm trying to learn electronics so I hope to be in it for the long run. So any help is appreciated!



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[a.ekholm]

Does anyone have any idea how to proceed? And what may have caused the burnt components?

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[Rasz]

usually its power supply that dies first in those speakers
disconnect it from main board and check voltages, afair one of the pins powers it up, otherwise you will only get standby 5V

BUT, since pcb is charred you will have to dremel out substantial part of the pcb and bodge connections to replacement amplifier chip, and lets not forget logi 5500 is a shitshow of a speaker system (10% THD)

[Chris56000]

Hi!

I realise this thread hasn't been dealt with for over four months, but I felt I had to offer this suggestion!

How about using one of these kits:-

https://www.ebay.co.uk/i/282980639214?chn=ps&adgroupid=51701849453&rlsatarget=pla-413069991248&abcId=1133946&adtype=pla&merchantid=6995734&poi=&googleloc=9041126&device=c&campaignid=1058609649&crdt=0

. . .to repair the subwoofer?

A set of four would be less than £15 (free shipping!), and it shouldn't be too difficult to trace the Audio and Power Supply terminals
from the original damaged PCB and use four screened cables plus a twisted pair of 16/0.2 cables for each replacement module!

Chris Williams