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,

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

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

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

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...

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

As I made the test before re-assemble the sub, I do it this way, like I do it before too. And this way it works, also I think (I don't have leave the Sub on for a long time..)
Perhaps you're right, could be on a bash board... I will try it again alone first.
But I need to take care, I only have 5 fuse left...


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)

OK, also this "behavior" is normal !

Some (bad) news today : as said, I tested again without the two DASH board connected, as I do it before and believed it was repaired.
So, fuse replaced, powered on. LED on back, green, as always. Red light on remote controller, on, as always.
Powered on with button : master light on and volume leds on... then I heard some crackling, then it began to smoke ; remote controller was still on, I switched it off manually. (After I check the fuse, it has blown, but it was really me who powered the "thing" off )

I dissamble the power board, and visually check the board (I tryed to smell too, but all the board smells "burned" now)
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)



This post has been edited by rsseco: Aug 17 2016, 12:15 AM

Thanks for new advice. I will check it tomorrow. 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 ?

Cu

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 ???

Tested again all 4 D's : they're OK (non conductive). 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 ?

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.

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 ?

This post has been edited by rsseco: Aug 21 2016, 02:58 AM

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.

This post has been edited by rsseco: Aug 23 2016, 12:53 AM

Here I am again. And here are the today's results (and a lot of results !)

First, I began to remove Q3 and Q4, with the heatsink.


Q3 and Q4 broken !

I took an another multimeter to do this series of tests :

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)
Q3(D) = Q4(D)
Q3(G) -> Q4(G) = 1.19 kOhm

Q4(S) = C69(-)/C70(+)/C60(+)/C59(-)
Q4(D) = C69(+)/C59(+)
Q3(S) = C70(+)/C69(-)/C60(+)/C59(-)
Q3(D) = C69(+)/C59(+)

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 (- -> +)


Values in other way (+ -> -)

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 !

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...

This post has been edited by rsseco: Aug 24 2016, 05:10 PM