I have 1 unit S750 faulty woofer, who wanna take it?

So, I've check the resistance between 1&3 pin of D3, D5, D2 and D4. They are all conductive, with about 1 ohm  !

But... Where is D1  ???

No power, I think power supply spoilt.
Sure, you want?

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Sometimes, only at first touch with the black leg, I've got a value, but only a fraction of second (then it shows it's non conductive)

Tested with component already soldered on board, I'd like to precise.
OK, I've seen the inscription on the board, it was hidden by the heatshrink.
I've tested this component too : red probe leg on the last (or first) pin, and black on each other pin : passive in one way only, 3 different values of resistance.

And finally, I tested the two Q3 and Q4 : I confirm, they are out of order (conductive in all ways !)

So, now what could be the matter ? 

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see pictures :


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I begin to check some components  :
D14 is ok
R14 have 980 ohm
R15 value is always changing, and decreasing
R37 have 5,9ohm instead of 10  ?
R29 have 89ohm instead of 100  ?

For the rest, I must first remove the heatshrink, then I will remove the two Q3 and Q4 and will recheck all these values.

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  ?

Just to remember, at the origin of the default, only C70 has explosed/leaked, the 3 other caps were only "bombed". Will the problem not be on the "road" to it  ?

And only one of the IRF740 was defective, why are they now 2 which brake down  ?

Ok, the only thing I will remove before runing this test, is only these 2 components ?

When you write "power on", that's mean : replace fuse, power cord in (to AC outlet), main power switch on ? Or the same, incl. power on via control pad ?

Is there no risk to blown the fuse again, despite Q3 and Q4 are left ?

The big caps are new, yes. The only thing which change compared to original, is they're 250V instead 200V.
C61 is original cap (I don't know why I removed it...). You think it could be the faulty one ?

Today was THE day !

And finally... it's alive again !
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Edit : I check Q3. It seems the "burn" comes from...
- Q4 have split ! (between ceramic and the heatshrink)
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Hi, I was a bit busy this week-end, so I haven't done the new tests yet.
But I can answer some of your questions :
I just hope I will not make more damage on the board/toanother components !
For degraded glue, I think there is no more on this power board. But on the others board, I didn't clean it.
I will try to explain you as cleary I can, with my poor english !

For the story before this day, and in order to make the work easier, I removed the all electronic board from the subwoofer housing (the wood housing). And for do this, I desoldered the speaker (3x cables)
So I had only the back plate with all board attached to it. And the power board wasn't screwed on this back plate.
Before I found that Q3 or Q4 were brocken, at the time I replace the capacitors, I have done a test (as you ask me to do the last time) without the 2 dash amplifier board connected.
So, coming to this D-Day :
- I began to replace the capacitor at the same place as original (before, I "deport" them). On C61 and two of the "bigs", I had to do the "L" method with a short piece of cable, as I hadn't the ring on the back of the board. After the capacitors were on position, I checked if all the pole were conductive :  they were (and it's at this time that I noticed I had a short circuit between a - pole of one cap to a + pole of another...)
- After that, I screwed back Q3 and Q4 on the heatsink, and then I replaced the all thing on the board back. I first soldered back Q3 and Q4. After all was OK, I wanted to screw back the other Qx ... and it's a this moment that I didn't found the screws anymore.
- So, in order to test the repair, I decided to take some screws with spacers from the uppers transitors (Dx ...)
- I connected the PSU board on the "main" board (and that's it), connected only the control pod, replaced the fuse, checked if main switch is on 0 position and connected the power cable in the outlet.
I check too if the 3 cables to the speaker aren't shortcuting.
- Main switch passed on 1 : green LED on back plate : ON ; red LED on control pod : ON
- Powered on via control pod : amber of master going ON and volume LEDs too ! I waited on this state 4-5 s (before, after max 2s the fuse blowned). So, as I had removed the screws from some transistors, I didn't want to wait on power on state for a while and switched it off. For me it was repaired at this time, as the fuse was already OK.

- The next day, I searched some screws with spacers (I dismantled a PC PSU to do so) and the evening I reassembled all back (I had soldered the speaker the day before). And as said, for me it was completly fixed, I didn't tryed it before and had closed the subwoofer with all screws, took it at place, connected the soundcard and all speakers cables and... powered on...1...2...off !!! The rest of the story, you know it !

I have already checked this, on all Qx : no, they are isolated from the heatsink.

I check if any shortcircuit were between the two aluminium spacers which fastens the psu board on the L-aluminum plate : negative too (I thought it could comes from this, as my tests were done without this aluminum plate.

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What I'm really wondering is, if you could check the list included in this post and see if I've added all the correct components and correct quantities, and if I'm missing any other ones that could be required for one complete repair job? I'm thinking I might as well replace all the old cheap brand capacitors so that these will last as long as possible when I've repaired both of them. I will order 2x the amounts ofcourse since I have two sets and probably a few extra of most of them just in case.

My list can be seen directly at DigiKey by this link: http://www.digikey.se/short/3ht51q

And here is the list in text:
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This night I thought about a thing I didn't tell before, because for me, it was "normal" (as I had this symptom often by the past) :

My S750 had this annoying "problem" (as said, before it does break and was working perfectly) on power on : often (not always) when I powered on the set via control pod, my set powered on and immediatly off. You could hear the relay "clicking twice" shortly.
It's as I "double press" the button, but I didn't do. A new press powered it on "normally".

After I repaired (also I thought it was repaired), it does the same thing on the first start...

But yesterday, as said, I powered it on 3 times, and never I had this symptom.
And what I found bizarre too, is after powering off/down, the relay takes longer to "click" (5 to 10s after red led is showing the off status). On power on, no problem, the relay clicks immediatly.
I don't remember anymore if on power off it should do the same or not. Or, perhaps it's as Q3 or Q4 are left, so it takes longer ?

If it can help...

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I used the "sound" parameter to check shortcircuits, Diode for diodes, Ohm for resistors (and sometimes to check shortcircuits) and V continious for voltage. The Diod gaves me values in V...

So, here's a look of the board without Q3 and Q4 :


Closer to Q3
And closer to Q4

Following results are without Q3 and Q4, PSU board alone (not connected) and no powered.
= means conductive, or shortcircuit.

Q3(S) = Q4(S) = C59(-)/C69(-)/C70(+)/C60(+)
Q3(D) = Q4(D) = C59(+)/C69(+)
Q3(G) -> Q4(G) = 1.19 kOhm

Q3(G) : N/A to all +/- capacitors C70/C69/C60/59
Q4(G) : N/A to all +/- capacitors C70/C69/C60/59

Values :

- R37 : 5.1 Ohm
- R29 : 98.1 Ohm
- D6 : + -> - or - -> + : N/A
- D7 : + -> - or - -> + : N/A
- D14 : - -> + : 0.47V (conductive) / + -> - : N/A
- R16 : 98.6 kOhm
- D14 : - -> + : 0.47V / + -> - : N/A
- D10 : - -> + : 0.56V / + -> - : N/A
- C54 seems to be OK
- C15 seems to be OK


Values in "normal" use of diods (- -> +) the direction is actually '+' to '-'


Values in other way (+ -> -) the direction is actually '-' to '+'

Values of Q6 (compared to Q5) :

Some other results :
Values in "normal" use of diods (- -> +)
Values in other way (+ -> -)

- D8 : - -> + : 0.11V / + -> - : 0.11V

So, going now to test bench : Control pod in, AC inlet (new fuse), PSU board not screwed to back plate, no heatsink on Qx and no Aluminium "L" plate, no DASH amplifier board connected.
And main switch on 1 :


And finally, powered on :

And, yes, despite Q3 and Q4 are left, it's alive ! And keeps alive for minutes, without any fuse blown ! And I powered off and on twice, no problems !

Here's the measurement :


Results :

- D1 : 323.6V !

- R2 : 157V

- Q3(S) - Q3(D) : values changing / -/+ values (alternative voltage ?)
- Q3(S) - Q3(G) : 285mV

- Q4(S) - Q4(D) : values changing / then seems to stop at +147V
- Q4(S) - Q4(G) : 287mV

- Q1(S) - Q1(D) : 168V
- Q1(S) - Q1(G) : values changing

- Q2(S) - Q2(D) : 173.5V
- Q2(S) - Q2(G) : 0V

- C70 : 172V
- C69 : 150V
- C60 : 172V
- C59 : Values changing / +/- mV and V

That's it... one thing is good, that it hold "on" for these tests of measurments. I haven't soldered any new IRF740 on Q3 and Q4 again yet, wainting for your analytics !

And to respond you (your last question), I check if I hadn't any shortcircuit between Dx and Ux and heatsink : negative !

Mine are not so high, they measure 22x40mm ; here was the link where I bought it : https://fr.aliexpress.com/item/Free-shippin...08.0.124.KGRgpw
After, I don't know if they are "real" or not ! Could it be an old series ? Or as you expected, they could be contrefacted ?!?

The best way to avoid this problem is to use reputable suppliers, like Mouser, DigiKey, Element-14, etc.

My terms are wrong ? Sorry.
But my thoughts are true to say marked side is - pole ? So, normally I always put the Black - pad on this side to have the normal behaviour of the diode, or am I completly wrong ?
Are some of my measurments totally wrong then ?

What should I do next ? Could be I must buy some other capacitors if they are "false" ones ?

EDIT :The fault can be mine too, as I want to buy as cheap as I can... I do it this way, as I doesn't want to spend too much in case my repair will not work.
I know it's a risk by having some bad quality product, and it's a dilemma : Low price = bad quality = perhaps repair will not work because of that ; instead of more expensive = best quality = can work better !
If I was sure to be able to repair it by myself, I would buy things of higher quality, of course ! 
Because usually, I always buy the best things...

Thanks a lot of checking my list! I've replaced the components with your suggestions, since I'm a novice I'd rather go with the safer bet. I've made an updated list here (containing enough for 3 subs), the customer reference is the amount needed for each sub. I'm not sure if I got those resistors from this thread or a friend of mine who looked at the sub, since they aren't that much I'll get them and see if I need to change them or not. All should be covered now right?
http://www.digikey.se/short/3htn1f

Also for the part I missed, is there any part that would have longer than 3000 hours? The other parts I have range between 5000-1000. Would for example this part work?
http://www.digikey.se/product-detail/en/ni...16-1-ND/4320150
It's a bit bigger and has a different ripple current and impendence, but the rest is the same. Not sure this moment where on the board they fit and if there is space and if those attribute differences are ok?

OK, I will check this with only Q3 and Q4 soldered. Do I need to try with only one first or can I put the twice together ?

And how will we find what ?

This is not what I already done yet ? Or you mean with some IRF740 in place ? Or in the order you wrote it : first V(G-S) and then V(D-S) ?

No, values fluctuated to fast ! I can try the "A-Hold" mode of the multimeter

I don't know what to say, the "-" sign appears sometimes...

OK. And so could be my IRF740 too... and perhaps what I doubt before, could be faulty or fragile too (that's why they broke as easily ?!? ; and could confirm my guess about why 2 IRF740 broke as before, only one was really out of order).

But, my fluctuate values without any IRF740 in place could reveal any other problem anyway ?

In fact, I don't know which was OK at the first time, as I remove twice at a time to check them. I only know one was defective and the other no
To remember :

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- D1 : 323.6V !    Okay

- R2 : 157V    Okay

- Q3(S) - Q3(D) : values changing / -/+ values (alternative voltage ?)          Vds of Q3 should closed to voltage on C59/C69.
- Q3(S) - Q3(G) : 285mV

- Q4(S) - Q4(D) : values changing / then seems to stop at +147V
- Q4(S) - Q4(G) : 287mV

- Q1(S) - Q1(D) : 168V
- Q1(S) - Q1(G) : values changing

- Q2(S) - Q2(D) : 173.5V
- Q2(S) - Q2(G) : 0V

- C70 : 172V
- C69 : 150V
- C60 : 172V          Voltage on C60 equals voltage C70, as expected.
- C59 : Values changing / +/- mV and V          Voltage on C59 should equals voltage on C69, like Vc60 = Vc70

Yes and no ! In fact, I've done it by putting the black pad as you wrote me before.
You can see it on this picture (S is written in black, D and G in red) ; I've tested it this way.

Okay, G seems to be written in black... but in fact, it's red !

I have an additionnal cap leaving (as I bought 5) ; should I try to replace C59 in order to see if I have stable value ?

Hi  !
Sorry for the delay, but with these hot summer days, not very easy to do some checks  !
By the way, here are the new checks of today  !
I re-check Q3 and Q4 completly again.
Q3 S->D  :  152V, no more fluctuating  !
Q3 S->G  :  283V

Q4 S->D  :  148V
Q4 S->G  :  280V

C59  :  157V but decreasing slowly

I wanted to re-check Q2 and Q1, but on Q2 I ripped the red probe between G and D and what should happen, happened  !  Shortcut, electric arc and Q2 explodes  ! 

For the other 2, I already threw them away...

But I don't understand why this time I haven't no more fluctuating values  !? !  So next step is to replace Q2, then Q3  ?

Edit  :  but, if it's mV, you have said it's too low too, so where is the matter now  ?

Hey, I'm working on soldering on my first set now that my components have arrived. Looking over my list I haven't actually found the location for two of the components.
* I've only found one of the 47UF 25V, the one next to the 35UF 100V, where is the other one?
* The only 0.1UF 50V I can find is a cylindracal one (similar to the others), but the one I've got on my list is a small yellow ceramic capacitor (this one: http://www.digikey.se/scripts/DkSearch/dks...81768803203599). Is this the one I should replace? Is that ok that they are so different?

Thanks for any help!

Interesting! I actually looked under that rubber tubing and found a Yageo 47UF 63V. Could it possibly be that this one isn't an original? This set was actually in for repairs a number of years ago, but I only noticed one other fix that they actually did, but could I be sure that this one is also part of that fix then? Should I leave it be or put my 47UF 25v there? See picture. Also, is this tubing important to get back?

Also one more question: On my list I had 3 1000UF 100V, but looking around I can only find two of these, one on each amp. Is it just 2 or am I missing something?

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I will order 2x the amounts ofcourse since I have two sets and probably a few extra of most of them just in case
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