Hey lex,

thx for the thread and your hard work.

I had to repair my S750 after it doenst work anymore for half a year now
I just startet to diassable the whole boardplate and after the first hope of just some damaged capacitors, i searched for an guide and found this thread. THANK YOU

I found no issue on the board, except of the glue.
I tried to remove all of the glue and my sharp leatherman knife was really good for this.

After i cleared up the board i discovered a hotspot.

back:


top:


After i build all together i checked, nothing...

Then i checked the fuse



I pluged i a new one and the board greeted me with a nice flash and i switched it off again

The flash was exactly at the hotspot and i had to clean it up a bit more, because the glue had shortcutted the capacitor to the mass.

After that it worked perfect again. THANK YOU AGAIN

Greetings
Psyotic

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.

any help is appreciated, and if anyone wants money for fixing it, let me know.

• My own repairing experience told me that could be the problem of C61 capacitor and/or the D9 diode neerby, I mean these two .
  
• And there's one time that I may made a short circuit between the heatsink of AMP board and it's aluminum support box, it also caused power LED blinking issue.
  

Any chance I can bought it? My own repairing on PSU board seems ok, but now I have another issue -- there're no sound (actually it's low volume distort sound) on SideLeft & SideRight & Center & Subwoofer channels, these channels are all connected to power amplifier board 2, so I'm thinking to bought another AMP board 2 or a failed set to replace it.

lex seems received a pack from oversea, he is definitely the right guy you want to sent your speaker to him to repair.
If you prefer local repair service, I think you can try search on internet (I found several S750 repair service provider on taobao -- eBay like website in China)

True, I'm satisfied with the sound quality of S750, that's why we all want to fix it instead of buy another speaker.

Hello @all !

If I write here, you can think a have a trouble with my S750 set.

In resume, it works well for many years (~12 years) ; for a month ago, I wanted to start my set again, after so many weeks off (but it was always connected to the AC outlet and in standy mode) ; as I pressed on the power on button of the remote console, I heard a "pffff"-sound, then all switched off.
I check the fuse : it had burned. I also opened the subwoofer, and it very smells badly. Yes, a cap had explosed ! And guess what, it concerned the 4x 470uF 200V, the C70 one. The 3 others were bombed, so I decided to replace all 4.

After reading so many posts, I clear all the "burned" glue everywhere I could and replace the 4 caps and the fuse.
Pluged on power outlet, switch on : the green led on the back turned on : check ! But I heard a "boom" sound. As the leds are still on (green on back, red on console), I decided to power on : it powered on, 2s... and then total black out. The fuse has burned again.

I open it again, but nothing "bad" to see.
As, when I replaced the cap, the negative "port" under the board were broken under 2 caps (I checked, all were conductive), I decide to remove all the caps and deport them, as you can see on the picture.

But again, the same story : when pluged in, the green led powered on. No more. But, when I power it on via console, after 2-3s all goes off, the fuse burn. To notice, I've glued the caps, the first one (c70, which one has explosed, had "jumped", but not explosed.

My electronic knowledge are very limited, so I don't know whats wrong. I tested the port on the caps ; I have a short circuit on the C69 and C59 (the 2nd and 4th ones). I visually check all the other component, they're seem to be OK. I tested the PSU board alone (the 2 DASH board were deconnected).

I really want to repare my set (and not throw away), can you please help me ? What can be the problem ?

I post some pictures if it can help you
















Thank you in advance,

Disclaimer: I'm not a professional electronic engineer, not even an amateur, so, take the advice at your own risk.

Okay, it seems the standby part of power supply board works ok (C61 is not been made a short circuit or open circuit)

Your description may already point out where's the issue came from.

Did you check the solder point of C59 C60 C69 C70 legs on both sides carefully before you "decide to remove all the caps and deport them"?
You don't want to connect the solder point with the copper around - that will make a short circuit.

This post has been edited by asenrzhang: Jul 17 2016, 03:14 PM


Attached thumbnail(s)

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

Here's the rest of the pictures :





This post has been edited by rsseco: Jul 19 2016, 12:09 AM

Disclaimer: I'm not a professional electronic engineer, not even an amateur, so, take the advice at your own risk.

The solder pads looks ok to me.

I looked again at the power supply unit schematics of Creative S750, my wild guess is Q3 and/or Q4 and/or R2 could been failed (my guess could be totally wrong).
You may check the resistance between S and D leg of Q3 and Q4 first after desolder them. Then check the resistance of R2 resistor.


Not all diode types act like that. I'm not familiar with this too, I learned in this thread and know that there're at least 3 types: ZENER & DIAC & typical diodes on PSU board.
Maybe the wikipedia page [English] [Français] can help.

This post has been edited by asenrzhang: Jul 20 2016, 01:34 AM

Thanks a lot.

I will check all this week-end. As a first fast try, 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 ?

This post has been edited by rsseco: Jul 21 2016, 11:09 PM

Disclaimer: I'm not a professional electronic engineer, not even an amateur, so, take the advice at your own risk.

When R2 is not been desoldered, the test result should have same reading value as when you testing C59 and C69 solder pads



I hope someone professional can help you choose a proper multimeter.

I bough a cheap meter (Chinese page) (￥84, or $13 ) too for repairing my subwoofer, it can be used to test capacitance too, max 2000μF, capable to test the big capacitor on amplifier board which is 1000μF. So far I'm satisfied with it. But professional engineers may not using such multimeter to test capacitors, especially electrolytic capacitors, if electrolytic capacitors are leaking, it will got a higher reading than it's real capacitance (see my post on badcaps.net).


Could be, but usually not I guess.

Before testing Q3 and Q4, you need to switch the multimeter to 'Diode' position.

I can only tell that it's failed if D(red pin)→S(black pin) is conductive (as your test result before, almost 0 ohm).

I can't tell the normal reading thought, the datasheets [ST] [Vishay] does not tell the resistance when it's state is OFF.
But since it's a diode between S and D, it should act like a diode when it's not failed: S(red)→D(black) should be conductive (several hundreds ohm 0.4V-0.8V bias voltage reading), D(red)→S(black) should not be conductive.

This post has been edited by asenrzhang: Mar 26 2018, 11:54 AM

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...)

This post has been edited by rsseco: Jul 24 2016, 10:03 PM

Disclaimer: I'm not a professional electronic engineer, not even an amateur, so, take the advice at your own risk.

Well, it's doesn't matter now, just throw the failed one away

You can buy more components for backup if it doesn't hurt . (Note: If you're buying from internet market, make sure you don't buy extra quantity -- if you bought 1, the seller may send 10, so you only need buy 1 in such case -- the aliexpress page you posted is such an example )
When I repairing my subwoofer, I bought a lots extra components, because the delivery fee is more expensive than the components fee . For example, I bought 100 fuses & 100 1N4004 diodes (for replacing D9) which I only need one of each

Hope you don't have other failed components. If it's the only component failed, your subwoofer should work again after replacement.

Since IRF740 is the model name of this component, different manufactory/company (SGS-Thomson (ST), Vishay, Internationa Rectifier, ON Semiconductor, etc...) can manufacture it, so they should be same.

If 'I R' you mean "I(a diode symbol)R", then it's the logo of International Rectifer company (it's Infineon now: 2015-01-13 Infineon Technologies AG successfully acquires International Rectifier).
I don't know what's '345F' means, maybe it's a product line number, I don't know... Other marks may used for manufactured date (week of year) or country.


If you have an old working one in same model (IRF740) & same package/case (TO-220-3), that's will be the quickest way to replace it.

If you don't find an old one, maybe you can try local electronic market first, or try buy from a local reseller on internet market, that could save a lot shipping time.

(Note again: if you buy from the aliexpess page above, you only need to buy 1, because it's a 10pcs deal )

This post has been edited by asenrzhang: Jul 29 2016, 12:02 PM

Just to say I'm waiting the MOSFETS... Everyday I hope they come, but no.
Perhaps tomorrow !

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.

This post has been edited by tezro: Aug 12 2016, 12:57 PM

Congratulations! I'd like to see every dead S750 subwoofer been revived!

Maybe you need a small components box with some grids in it to store these screws, like the following


This post has been edited by asenrzhang: Aug 12 2016, 08:52 PM

I found one on eBay a month ago, it's still available now.
http://www.ebay.com/itm/322220223412

I tried to buy it, but since I'm newbie on eBay (zero feedback), the owner cancelled my bidding

Thank you for the link bro.

Not sure if i really want to bid the e-bay s750 sub. I think the shipping will cost a bomb.

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 ?

This post has been edited by rsseco: Aug 13 2016, 02:10 AM

Sorry to hear that, I guess there're still issues somewhere.

I think you can isolate the issue on power amplifier board first:

1. Check potential failed components, at least check same component which failed last time. If failed, replace them.
   
2. Replace fuse
   
3. Unplug CN4 & CN5 connector on power supply board, this will isolate issues on power amplifier board
   
   
4. Power on again
   
   • If fuse is still blown, it indicate there're still issues on power supply board.
     
   • If fuse is not blown, you may check power amplifier board now.

I'd like to help if I can. But I can only diagnose very basic issues.