Bose SoundTouch 20 - IC identification

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cmaxwell

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A friend asked me to look at his Bose Soundtouch 20, that wont turn on. He is shocked that something so expensive could be working fine one day and dead the next.
An IC on the back of the amplifier board has seriously deceased, so I have no idea what it was. I know its a slim chance, but fingers crossed someone has one of these boards lying around, and could identify it? Many thanks if you can help.

 
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Unfortunately Bose are just cheap Chinese gear with an expensive price tag, and they don't supply spares or information - pretty well all the electronics trade refuse to accept it for repair for that reason.

I'm presuming that's the switch-mode IC?, so it's almost certain a number of other parts will have been destroyed as well - the chip itself it probably just collateral damage from something else having failed.
 
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Yes, I realised that the IC might be the cause of the problem, or that the problem might have destroyed the IC.
With an eyepiece I can see that most of the top of the IC is destroyed. There's a tiny little bit which looks like the bottom of a Texas Instruments symbol, but that's it.

Thank you both for looking at this.
 
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As Nigel said, that is part of the switch-mode power supply.

If there aren't too many output voltages, it might be possible to disable the power supply and to fit another one in the box, and wire the power to the amplifier board.
 
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Thanks Diver300. I will look in to that. I'm very tempted by Nigel's statement "pretty well all the electronics trade refuse to accept it for repair" and tell them to bin it.
 
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Thank you so much for that link, rjenkinsgb.

I couldn't find that manual at all before. I found one for the Soundtouch 30, but that didn't help at all.

I will order that IC. I realize that it might be a victim rather than a cause, but its worth a go.
 
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Check the datasheet for the chip - it will give you some ideas. It's almost certain that the power FET has gone short, and that has destroyed the chip - no point changing the chip without changing the FET. There may also be other blown parts, check what you can.
 
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Yes. Thank you, I will do that. To make the order worth while I will any parts that seem related to that bit of the circuit. My knowledge of smps is about zero (my background is in medical electronics), but over the next few days I will remedy that.
 
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cmaxwell said:
Yes. Thank you, I will do that. To make the order worth while I will any parts that seem related to that bit of the circuit. My knowledge of smps is about zero (my background is in medical electronics), but over the next few days I will remedy that.
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The actual design is rather unusual, as the FET is fed via it's source, rather than it's gate (as is usual in SMPSU's) - so it's not hard to see that if the FET goes S/C then you get full rectified mains on the chip, and any other associated components where current might flow. This is why the chip has exploded so well

Mainly what you're checking for, and mostly it can be done with a multimeter on ohms, is O/C resistors (blown by the huge surge) or S/C diodes, again died in the surge. Any electrolytic capacitors in the primary should be checked as well, plus the secondary rectifier diodes, sometimes a short there can take out the PSU. A less obvious cause can be the reservoir capacitor (the large one), if that's O/C or extremely low capacitance, then sometimes (on certain designs) this causes the PSU to blow up.
 
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Hello Dear
i from INDIA , i also faced same issue with Bose Sound Touch 20 , however i have another bad ic in front of this board as its completely burn so cant read IC number , my humble request to you if you can please send me Front Side Photo like this one so that i can read IC number .
My Email Address is Deleted. It is a bad idea to show e-mail addresses in open forum - Moderator
regards
 
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