Good Day all

I followed the steps in the whole forum to repair and upgrade my S750 surround system but it didn't work

my problem wasn't directly with the power board, when my speakers started to die I turned it on one day then I heard sound of something exploding, then the sounds turn lower and the right channel was buzzing
after that day my sound system always turns on but have this buzzing sound problem.

after reading what's written I decided to upgrade the whole components, I checked on the power board, it seems to be OK, no fat Capacitor or burned Diodes or exploded stuff, but I noticed the two Capacitors on the Amp Boards in sector C40 blown and burned.

what I did that I changed most of the parts in the power supply board then some capacitors in the amp boards according to this list (founded earlier in the forum)

https://onedrive.live.com/redir?resid=E2DDC...int=file%2cdocx

- First Repair Results:

power on functioning correct and nothing exploded, but there's no sound at all from any speaker out !! 

- Possible causes:

1 - some soldering points where so fragile, I may have cut/ruined the copper connections down some components on the power board within soldering?
2 - other contact point on the amp board where visibly damaged because of the hot soldering and I tried to fix them, but I got the same results (that didn't encourage me to continue replacing the capacitors in the amp boards)

- Reviewing and Checking for any possible Visible problems:

re-check on every soldering points, cable connections... no visible harm, nothing more to do !! 

Please Help me find what to do else to complete this mess, I'm so disappointed and exhausted from trying to find the problem with no results regarding that I spent 120 euros to buy the components and feeling useless unlucky.

I can uploads photos for every thing I solder on the boards, please tell me what to do 

Thanks
Homer

Hello while I was scraping the conducted glue I scraped off the green layer like in the imageσ below.  Also the pads are gonners and I made some with your methods...  Can you please tell me if I am doing something wrong or if I will have problem without the green layer cause i i tried to turn on the system and i saw a flash. You can see the blown part on the white surface in the 1st image.

Unfortunately the back of my pcb doesnt have any pads also how can i connect the capacitors on the back on the down side?

Is there a chance my capacitors are blown now due to the short circuit?

I just finished the soldering and modding of the solder pads and my s750 is working again . Thank you for everything you have been a BIG help! There is only one problem though... My bass is not woriking as it was. It is not making loud bass sound, almost not hearing it at all sometimes and i need to enable the bass boost option on my sound card and when i disable the bass rederection i hear bass sounds from the surround speakers...    

Hmmmm ok i will try this method mate, although i have never touched the woofer and it was working perfectly till the system started doing the blinking green power light. I will dismantle it and i will try to remove this massive glue on the pcb. Thank you again for your help.

I just cleaned most of the degraded glue on the sound I/0 pcb and checked on the subwoofer for any problems but i found none. The strange is in CMSS-3D option of the sound card program, if i enable it or no i see no difference and if i raise the bass % from 50% to 100% i hear more bass coming from the satellites instead of the subwoofer and the sound is becoming way too bad...

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5. Occasionally, there's no sound of the relay after power on button is clicked -- so no power.
  The LED light on subwoofer is steady green, after clicked standby/power button, the LEDs on remote control pod are green too, it's seems power is on, but I can't hear the sound of relay.

Hi

new guy,  no electronics experience.  Got an S750 that just packed up when I plugged headphones in,  the green power light still blinks,  but the red control unit light won't come on.

I actually have another broken unit as well that has no green power light working - I kept it after buying a new one in case I found some one who can repair them.

Is there anyone here who can repair it for me - for money - of course?

or does anyone know any good audio electricians who might be able to do it for me? 

Anywhere in the UK,  I think overseas shipping might be too much - but not actually sure.

There's nothing comparable on the market at all at the moment,  and I REALLY like this setup.

...
As the leds are still on (green on back, red on console), I decided to power on
...

...
I have a short circuit on the C69 and C59 (the 2nd and 4th ones).
...

Thanks for your fast response.
Yes, I did check them, but to be sure, I have remove the capacitor once again to verify ; I already "scratched" with my fingernail to clean around the point holes.
Some pictures to show :

...

Tested on both side, and Xcrossed too (one test pin on top, other on bottom). I always have this short circuit in cap69 and cap59. This short circuit must come from somewhere else, but from where ? Is it possible another component is "broken" ?

Last time, I began to check the diodes, some of them were passive (- >+ and + -> -). As I can remember me, a diode is only passive in one way, right ?
Thank you

...
I checked the R2 (nothing has been desoldered yet) : I have a little value (<1K) before it goes to 0kohm. So it could be dead as you guess !

For comparison, I've check the same resistor (R23), and here I'm getting a stable value, but not the 33k as required (my meter tells me 28.9k, but it is not as precise as it could be, as it's a cheap multimeter. Additional question here, what model could I buy which make capacimeter too ? And not so expensive too : ~max 150 USD)

Are the C32 or C33 not to incriminate ? Or T1 or T2 ?!?  ?

I will check the Q3 and Q4 too see first... When you say "check the resistance between S - D", what sort of value must I find ? Must I determine if S -> D is passive and/or D -> S ?

Hi  ! 
Some news after testing the things.
R2 seems to be OK after Q3 and Q4 were removed.
And yes, one of both is NOK, S-D and D-S are conductive, the other one is good (conductive in one way only)
Unfortunately, I can't say which one was defective, as I removed twice before testing each.

So, I need to buy at least one IRF740 component (I think I will buy 2 or 4 to replace twice or all  ? ) what do you think  ?

I must thank you once again  !  And hope after replacement, my S750 will work again  !

Edit  :  there's a lot of irf740 on internet. I think they all act the same  ?

I have some inscription under the irf740 reference (I R 345F) What does it mean  ?

I found a bundle on aliexpress  :  http://fr.aliexpress.com/item/10pcs-free-s...308.0.40.a4K1j5

But I will try to found someones in old electronic stuff I have, perhaps I don't need to buy (the shipment does take too long...)

Today was THE day !

And finally... it's alive again ! Thank you very much !

But, as I remove the 2 mosfets for testing 3 weeks ago, I don't remember where I put the screws with the ceramic spacer to fix these mosfets...

Hi.

Anyone who has old faulty S750 subwoofer for sale?

I would like to buy one to get parts for my faulty S750 subwoofer.

Thank you.

I disassemble an old PSU and remove the screws and spacers from the mosfets inside. So, I mounted my S750 sub this evening. And finally, I said victory too early... powered on, 2s, and shutdown   
The fuse blowned again ! I'm disappointed !

So, let's go again to dissamble this shit again 

I think I will need your help again in the next days, if you're already ok ?

..
One thing which I found strange as I checked all component after I soldered the capacitor, on one (C69 or C60, I don't remember exactly) the negative pole was "shortcuting" the circuit under the board (I check if no solder was touching out the "round", it was OK). On two capacitors, I had to do the trick with some cable in "L"-shape so I could solder on the bottom (as you can see on the picture)

...
What I found :

- R36, in front of Q3 (replaced by new mosfet) seems to have burn. But not really sure it comes from the resistor, as I've got always 46.7 Ohm (same as R38, in front of Q4). On your doc, it says "47R, so it should be OK). I check (visually) the capacitor in front (C29), on one pin it seems have overheat too (but it's not broken). As I don't have a capacitor-meter, I measure the value in Ohm : I have 530 Ohm, same value as the capacitor in front of R38.

Edit : I check Q3. It seems the "burn" comes from...

- Q4 have split ! (between ceramic and the heatshrink)

see pictures :

My thoughts : are the IRF740 low quality/bad/defective (?), or problem is coming from somewhere else ?.
-> As I tested the old Q3 and Q4 and found only one bad, I can think there can really come from the new ones. (as wrote before, as I removed the two mosfets, I have replaced twice by new ones)

I think I must remove these components before testing, as always  ?

But D2, D3 are in the upper section of the board, is this section not designed for the standby power  ?

I re-check the specs of the IRF, they are designed for 400V, so as you say, it's not an over-voltage, as if the power value on this point not exceed this value  ? T1 or T2 could not be the cause  ?