Great guide Lex!


Here's my board after 10 years of owning the s750. 4 bulged 470uF caps(yes all 4) still power up as normal with very looooow volume. Like not enough juice to power the amps.











Stupid glue did a lot of damage except in the second pic.




This post has been edited by Cookie000: Jul 22 2014, 12:35 PM

Did you managed to fully revive the unit? Does it still suffer from very low volume after repairs? Check those 0R resistors situated right behind those big four 470uF 200VDC capacitors, in case the low volume problem still remains...

Looks like quite an amount of oxidation there (by the chemicals from degraded glue) as the copper layer looks dark and/or dull, instead of being shiny. After removing all those chunks degraded glue, try cleaning those exposed spots with IPA (isopropyl alcohol) to remove any remnants of chemicals from the decaying glue...

This post has been edited by lex: Jul 22 2014, 07:28 PM

Thanks for the reply Lex! Parts have been ordered from Digikey. Still waiting for the Fedex truck to arrive later today...
Cleaning the crusted goop is no fun

Here's my parts list:

Hi ppl, Hi Lex
First of all, ty for this epic topic, i'm learning alot and mb will have a chance to save my s750 too.
Now here is my trouble:
I've the same typical meltdown aka flashing green light and brown glue of death. I tried to remove it painfully and regulary test it. Obviously I made a short circuit and both of my c40 blown out
Now I'm on my way to change all part Lex recommended but I've a doubt about this c40: Kukruse said It's a 100v cap but his reference links to a 50v cap (in parlist.doc)
I'm already extremely lost in the number of parts and nomenclature, I hope you can help me with this c40 (or an exhaustive list for the whole pack but I can deal with research)
Ty in avance

C40? Is that a ceramic disc capacitor? If it is then usually that is 10nF (or 10,000pF) and the recommended voltage rating is usually 1kV since its part of the snubber network around the rectifiers...

It's the orange one burned here:


in the post of Kukruse https://forum.lowyat.net/topic/2873671/+80#
Is his partlist.doc looks good to you?

My studies in science and technical engineering are soooo gone

This is one of the power amplifier boards, and there are two of them. In fact both of them are identical. You can check the value of the capacitor on the other power amplifier board, in the same location. If that capacitor is in parallel with that big (1000uF 100VDC) electrolytic capacitor next to it, then very likely its a 100nF capacitor with voltage rating of at least 100V (following the big capacitor, can use capacitors with higher voltage rating also). Anyway, that capacitor may not be the only failed component on that board. Possibly that big (1000uF 100VDC) electrolytic capacitor next to it has some problems as well...

Ok thanks a lot! It should be the FK20X7S2A475K whitch is described as a 100v than the FK20X7S1H475K (50v) witch is on partlist.doc

Btw I'll change every old/bad lytics and glue before re trying. This glue is awfully stuck on board, I'm scared of scratching something...

This one is a 4.7uF 100V ceramic capacitor. It should follow the same voltage as that big capacitor next to it...

The one to get rid off are those that have turned yellowish to brownish color. The white colored glue is still fine, as its a different type of glue than the ones used on the rest of the boards...

I don't understand very well the condensator's role. The FK20X7S2A475K seems good but it's very difficult to buy. What did I have to check for a new one? Same size and voltage obviously (100V like the big one on the pic) and 4.7 µF like the parlist of Kukruse. Is that all? I don't know the difference betwin ceramic and lytics..

Actually you can use just any ceramic capacitor of the same capacitance (4.7uF) and voltage rating (100VDC). Typically I would choose NP0/C0G, U2J, X7R and X8R type ceramic capacitors (more stable across entire range of temperatures) rather than the cheaper Z5U and Y5V ceramic type capacitors (capacitance and impedance varies a lot with temperature). That big capacitor beside it is a general purpose capacitor. Usually if you find a ceramic capacitor in parallel with it then its one way which some manufacturers cut cost. Instead of using more expensive specialised low ESR/impedance capacitors, they would use cheaper general purpose capacitor with a cheap ceramic capacitor. The strength of ceramic capacitor is that it has very low ESR/impedance at high frequencies (typically in the switching power supply range). Thus that capacitor serves as a low ESR/impedance side to the bigger electrolytic capacitor (functions to bypass/filter and sink high frequency ripples off the rails that the bigger general purpose electrolytic capacitor unable to handle). And if the power rails are too noisy (often due to power supply failing) then that ceramic capacitor will be taking all the "heavy load" (trying to remove the ripples)...

This post has been edited by lex: Aug 29 2014, 01:06 AM

Hi Lex
I would be eternally grateful for your help, everything works!
I actually changed the big cap 450V on C61 and the cap 0.1µF 50V on C63 who are both dead (nothing on multimeter), C62 and C68 (they suffer too much from the proximity of the sink) and obviously I got rid off this glue (one off the most painfull work i've done ). On the amp board I've changed C40 (totally burned out), C39 (sligtly burned by C40), C81 and 91 glued to death...
Still have to replace the five 220µF and the five 100µF but It works!

Btw, I found the same problem I've before: The rear left output is down and I've some kind of cut in sound at higher level (above mid power depend of source) like a saturation. I can live without taking down the neighborhood's trinket but one way down is problematic...

Oh and thanks again for your advice that helped me so much ^^

This post has been edited by Shadowdace: Sep 5 2014, 05:28 AM

Glad it worked. Should give those speakers a new lease of life...

Have you cleaned the connectors on the power amplifier boards? Also you may have to clean the audio controller board and the I/O board (where the audio, control pod/dock and speaker connectors are located). Especially the I/O board, which is right under the audio controller board, has lots of degraded glue especially at the connector solder pins. That one is kinda hard to clean and require some proper tools...

I cleaned everything I could reach: Powerboard of course, degraded glue on both aux board (part brown, part white) and I cut the glue connexion between lytics on audio controller board (which is indeed the one on top with forty capacitor?). Some of the lytics still glued but no short circuit anymore.
Below audio controller, the I/O board contains two massives plates of glue: One top of the jack's enter, the other links the seven dual cable (red&black). This part requires desoldering the CN2 and CN4 line that I'm a bit afraid to do...




Do you think the soud's cut/saturation could come from C59/60/69/70 (or the 10 caps 220µF and 100µF on amp board) I have not change?

This post has been edited by Shadowdace: Sep 6 2014, 04:46 AM

Yups, those are the boards I've mentioned. Particularly that I/O board is just full of glue. I would recommend that you scrape it off, as there could be degraded glue hidden under it (and causing problems with some of the audio inputs there). If you do not want to desolder the board off (which is a lot of hard and difficult work, particularly since this is double sided PCB) then try usuing a thin long flat head screwdriver plus very fine but strong tweezers to remove those glue. Also remove any glue on the audio controller board especially those that cover the I.C pins. Have to be delicate as these are (delicate) SMD type components thus proceed with care and caution...

Hey Lex,

Really glad I found this thread as I'm really reluctant to give up on my S750's. Quite impressed that you've kept it going for over a year! Recently had a power outage at the house and the power kept trying to come back on. After the power finally returned for good, I had the dreaded pulsing green power light which then became no light. No power to the control box and no sound at all.

I should preface that I'm a complete newb at this electrical engineering stuff. Aside from a little experience soldering an "Ultimate Useless Machine" I haven't really done much and I've never had experience with finding faults on a PCB. I can't find any capacitors that have bulged but since you mentioned they're low quality I figured I'd replace them anyway and hope it fixes the problem. Would you mind taking a look at this project order on Mouser just to ensure that I followed your recommended replacements well?

One piece I noticed that seems a little off, which maybe you can comment on, are the resistors(?) at D8 & D13 (circled in the first photo). If they're supposed to look like D7 and D6 then they look like they're possibly burned out. If you agree, can you enlighten me as to what type of resistors those are? They don't follow the normal convention I'm used to seeing of colored bands on beige.

You mention a lot about removing the old glue, and I'm all but finished cleaning all the old bits of glue off (still a work in progress), but you don't mention anything about re-gluing. Is this something we should do after replacing capacitors? If so, how is that done? Honestly the board looks better without the glue so I'd be just fine leaving it off of there.

I've included some photos for your viewing pleasure. Thanks again for this post! I've found it incredibly helpful and enlightening.

First off, that 470uF 200VDC capacitor is of wrong dimensions. Its too tall at 50mm. Plus the originals are "snap-in" types. Thus please follow of the capacitors I've selected, which should be this one: Mouser > Passive Components > Capacitors > Aluminum Electrolytic Capacitors > Aluminum Electrolytic Capacitors - Snap In > Panasonic EET-ED2D471BA. And looks like that one is going to be EOL'ed (thus grab it while still available, because that one has one of the best specifications compared to the rest of the field)...

Those are not really resistors. Sometimes they are called 0 Ohm resistors (single black band means "0"), but they are actually fusible links (that looks like resistors)...

That glue to help hold the components (especially big ones) in place for easier soldering (in the factory). Other than that it has no use at all. Thus just remove those glue. And do not use anymore glue. The prolonged heat inside the subwoofer can degrade (cause chemical breakdown) those glue. Do clean with IPA (isopropyl alcohol) the areas where the glue was removed...

Thanks for such a quick reply!


Wow, thanks for catching that. I thought I was being so careful, there were a few different links around this thread and I wasn't sure about the End of Life thing.


Thanks for clarifying. In your opinion do they also need replacing? If so, is this what I'm looking for?

And one last curiosity question. When I bought the speakers, nearly 10 years ago, I was living in the US. Now I'm living in Europe. Is it possible to convert the sub to 220V and if so is it fairly easy to do? Is it possible to make it dual-voltage? 110-220V? (according to the input it's already 110-120V 50/60Hz)

Seems Panasonic decided to quit producing snap-ins. That Panasonic TS-ED series (actual datasheet here) has the best specifications among all, with ripple current handling of 1850mA@120Hz while the rest of the field have around 1400mA to 1600mA ripple current handling only (at 120Hz). Alternatives would be Nichicon GU series (which has lower ripple current handling)...

If they are not broken (should read as shorted on the multimeter) then no point replacing them. Yes, those are the "0 Ohm" resistors (actually fusible links)...

That standby power section may be able to automatically adjust to new higher voltage (since its a standard flyback design), but the main power section may not be able to use a higher voltage (does not seem to have any feedback section).

I just wanted to report that I followed your instructions to the letter and the speakers work again!

Mostly... now I don't get sound from the Center/Subwoofer or Side Channels. The speakers are fine, if I change around the speaker connections in back I can test them individually and all speakers produce sound. Likewise, if I swap the center/subwoofer (orange) computer connection into the front connection (green) I get center from Left Front and Sub from Right Front. It's the same with the side channels. So there is a signal coming from the computer into the connection, but it gets lost between there and the speakers.

Any thoughts?

Regarding my previous question about switching from 110v to 230v, I noticed in the Schematics for PSU2 a paragraph on Voltage Selection.


Based on this, is it possible I could pull the two Zero ohm links out and replace one at R31 only and get 230v or is it more complicated than that?

Thanks again for posting this tutorial. Really, very happy to have my speakers more or less working again.