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.
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.
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...
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I also have a 5i and I have no problems with the service manual, you can send me a copy via e-mail: vdidoff@gmail.com----'ll study the diagram and I can help you too.
Thankful.
Thankful.
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. Email:afhung37@hotmail.com
Thanks.
Would also like repair manual
Thanks, can i get a copy of the repair manual, email it to mik_b69@hotmail.com
Thanks again
Thanks, can i get a copy of the repair manual, email it to mik_b69@hotmail.com
Thanks again
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?
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?
At first you should disconnect the power amp from the supplies to check whether it is the smps or a blown amp.
I had to repair some old harman kardon amp with quite similar smps - and I must say these pulse-width modulated veteran circuitry was a nightmare by design.
They blow up during power on and I had to design in some additional circuitry to prevent this from happening.
All in all, quite bad designed smps.
I had to repair some old harman kardon amp with quite similar smps - and I must say these pulse-width modulated veteran circuitry was a nightmare by design.
They blow up during power on and I had to design in some additional circuitry to prevent this from happening.
All in all, quite bad designed smps.
Well mine just bit the dust, not sure how long ago but the surgistor failed (the green component with the top that blew off), not sure what else needs to be replaced, but imagine any component that has that hard resin touching it may need to be replaced (some of it is pretty dark brown but no signs of a burn mark).
Well mine just bit the dust, not sure how long ago but the surgistor failed (the green component with the top that blew off), not sure what else needs to be replaced, but imagine any component that has that hard resin touching it may need to be replaced (some of it is pretty dark brown but no signs of a burn mark).
What were the symptoms before it failed? As well, I am still looking for a service manual if anyone has one
I don't know what the symptoms were before it died, for all I know it died while watching TV and I never noticed it die.
What I have figured out is that a bunch of resistors, surgistor and this "RECT 1A2 60V DIAC" needs to be replaced. It's that DIAC that I can't figure out. I see that there is a "DB6" which shows up in another individual's photos here (http://www.diyaudio.com/forums/subwoofers/239417-need-help-psb-subsonic-5i.html#post3634247, the last photo) but the layout of his PCB is different than my 5i, maybe a different revision of the BASH amplifier.
What I have figured out is that a bunch of resistors, surgistor and this "RECT 1A2 60V DIAC" needs to be replaced. It's that DIAC that I can't figure out. I see that there is a "DB6" which shows up in another individual's photos here (http://www.diyaudio.com/forums/subwoofers/239417-need-help-psb-subsonic-5i.html#post3634247, the last photo) but the layout of his PCB is different than my 5i, maybe a different revision of the BASH amplifier.
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