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Old 07-09-2019, 09:25 AM   #1
BlueVelvet
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Smile Bose PS28 III Subwoofer Power Block need issue diagnosing help

Hello, like to begin with that I'm a complete novice but I've managed to follow certain videos online to help me fix this but I am now stuck.

The subwoofer is the Bose PS28 III.
Using this youtube video (https://www.youtube.com/watch?v=s9GarjV3zzs) I have managed to diagnose with a multi-meter that the issue may be coming from the power supply board (PN: 286612-002)

An older thread on this forum (https://www.badcaps.net/forum/showthread.php?t=65417) helped me find the schematics for the issue (although to be frank, I personally, have no idea what to do with that.)

I am able to follow the youtube video all the way until the 3:04 mark in the video (when the person starts to diagnose what specific components are shortened/blown in his board). I understand this is going to be different for everyone, however, my issue is that unlike the video (which seems to have very obviously identifiable issues), I am unable to find any blatant issues with the power supply board I'm working with. I'm hoping someone here can look at these pictures I've provided and help me see the obvious.

Photo album - https://imgur.com/a/0fjIG7v

Thank you!

Edit: I've noticed the images didn't upload in full res. I'll update soon with better photos.

Last edited by BlueVelvet; 07-09-2019 at 10:51 AM..
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Old 07-09-2019, 11:00 AM   #2
BlueVelvet
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Default Re: Bose PS28 III Subwoofer Power Block need issue diagnosing help

Here are better photos.
Attached Images
File Type: jpg 20190709_001240.jpg (786.4 KB, 28 views)
File Type: jpg 20190709_001302.jpg (753.7 KB, 26 views)
File Type: jpg 20190709_001526.jpg (691.4 KB, 19 views)
File Type: jpg 20190709_001557.jpg (583.7 KB, 15 views)
File Type: jpg 20190709_001608.jpg (690.9 KB, 10 views)
File Type: jpg 20190709_001618.jpg (643.5 KB, 8 views)
File Type: jpg 20190709_001628.jpg (762.9 KB, 6 views)
File Type: jpg 20190709_001648.jpg (592.8 KB, 7 views)
File Type: jpg 20190709_001712.jpg (714.5 KB, 9 views)
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Old 09-26-2020, 05:22 PM   #3
roberhoz
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Default Re: Bose PS28 III Subwoofer Power Block need issue diagnosing help

Check these components. Inside the circle marked in yellow in the image.
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File Type: jpg bose PS.jpg (1.23 MB, 18 views)
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Old 09-29-2020, 06:38 PM   #4
momaka
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Default Re: Bose PS28 III Subwoofer Power Block need issue diagnosing help

Could you describe what issue(s) you're having with your subwoofer?
I think that might help us narrow it down where to look.

The issue in the Youtube video you linked shows a blown amplifier power supply, which was repaired by changing the primary-side MOSFETs, MOSFET drive circuits, and PWM IC.
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Old 09-29-2020, 07:22 PM   #5
stj
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Default Re: Bose PS28 III Subwoofer Power Block need issue diagnosing help

nice design, wouldnt want c117 & c118 getting cold in the wintertime!
/sarc
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