PSB SubSonic 5i problems- no go - diyAudio
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Old 27th September 2011, 03:10 PM   #1
diyAudio Member
Join Date: Jun 2009
Default PSB SubSonic 5i problems- no go

Hello everyone, I am trying to repair a PSB SubSonic subwoofer that I bought recently for cheap (for obvious reasons).
I obtained the service manual and started doing some basic tests. Seeing that the amp wouldn't power up at all or show any signs of life, I decided to first test the power supply. This amp uses a SMPS that has a pwm control to change the voltage of the supply rails continuously with changes in the load.

I had a look at the schematic and tested the voltage at the specified points, only to find that pretty much all the voltage readings I took were no where near the specified voltage, leading me to believe the power supply is faulty.
Some of the voltages were higher, and some were lower than what they were supposed to be. Another thing that I noted was Q401 and Q402 would get very hot, too hot to touch and they only share a smallish heatsink.

Another observation was the the power supply is audibly noisy in operation, sounds almost like a camera flash unit as it charges.

I have a basic understanding of SMPS's operation, but very little experience with them and I do not know what the best route for repair would be. It is no problem for me to remove components either partially or fully to allow out-of-circuit testing.

From what I have described, are there any common failure points that I should investigate first, or is there a procedure to trace the fault? I could simply go through and replace all the semiconductors and capacitors, but I would no doubt be replacing a lot of components that were perfectly fine, along with no guarantees of actually fixing the problem.

Any help would be greatly appreciated, I hope to learn something from this exercise so I don't want to simply replace everything until it works, as I may not even fix it and spend money for no reason.
Perhaps a couple of components failed and caused a cascade where their failure triggered other parts to fail? I do not know, so I thought I would ask here as I'm sure there are some experts on the subject. Thank you for taking the time to read my post, if you can help in any way I would be most grateful for your time and advice.
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Old 27th September 2011, 03:56 PM   #2
diyAudio Member
Join Date: Jun 2009
Here are the schematics, was going to upload them in the original post but had to battle with reformatting and resizing issues, because the 195 kB maximum upload is sweet F-all and makes it difficult when dealing with .pdf files that are 10 kb too large to upload and can't be re-sized...
Attached Images
File Type: jpeg 0001Q7.jpeg (186.0 KB, 408 views)
Attached Files
File Type: pdf PSB Speakers SS5i-ServiceManual-1d1 (dragged) 1.pdf (178.4 KB, 293 views)

Last edited by flyingtele; 27th September 2011 at 03:59 PM.
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Old 29th March 2012, 05:33 AM   #3
Bigred is offline Bigred  Canada
diyAudio Member
Join Date: Jul 2007
I've got one of these subs in for repair. Does anyone or the original poster happen to have the service manual? It appears the two previous attached schematics above are not complete.
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Old 28th August 2012, 11:08 PM   #4
vdidoff is offline vdidoff  Brazil
diyAudio Member
Join Date: Aug 2012
I also have a 5i and I have no problems with the service manual, you can send me a copy via e-mail:'ll study the diagram and I can help you too.
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Old 19th September 2012, 12:59 AM   #5
vdidoff is offline vdidoff  Brazil
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Join Date: Aug 2012
Default Service manual PSB 5i.

I have a problem with Subsonic 5i, you get a copy of the service manual? If so can you send me a copy.
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Old 30th May 2013, 04:07 AM   #6
diyAudio Member
Join Date: May 2013
Location: Melbourne
Hi Guys, has any one had any luck on getting the service manula for the PSB 5i sub amp. If so would you be kind enough to email us the service manual. It seems like my one is not powering up pointing to a SMPS issue. The 1A fuse continuously blows when replaced. Thanks in advance!
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Old 3rd June 2013, 12:58 AM   #7
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Join Date: May 2013
Location: Melbourne
Thanks guys, love your support. I have also managed to get the complete service manual. perhaps it may help some one some day!!!
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Old 17th July 2013, 05:15 PM   #8
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Join Date: Jul 2013
Location: Perth
Originally Posted by Jim Filaktakis View Post
Thanks guys, love your support. I have also managed to get the complete service manual. perhaps it may help some one some day!!!
Hi Jim,

I'm in Perth & have a PSB Subsonic 5i which keeps on blowing fuses. I will be grateful if you can send me a copy of the service manual for this sub so I can try repair it.

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Old 4th September 2013, 02:58 PM   #9
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Join Date: Sep 2013
Location: Ontario
Default Would also like repair manual

Thanks, can i get a copy of the repair manual, email it to

Thanks again
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Old 27th February 2014, 02:17 PM   #10
p88 is offline p88
diyAudio Member
Join Date: Feb 2014
Default updates?

Hi, just wondering if anyone had success in identifying the problem and fixing it. The first time my 5i sub died (fuse would blow on power up), it was repaired under warranty. This time (no power light, but fuse is intact), I'm not sure its worth fixing.

Also, is there a way to post the service manual?
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