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.

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)

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.

I'm not Lex, but I just recently did this repair and I was just fine with a non-fancy soldering iron and solder wick (braid). Some of the pieces I did have to use a solder sucker to get the remaining solder out of the hole once the piece was out, but I don't think you need a sophisticated vacuum soldering station.

Hope this helps.

Hey Lex (or anyone that's reading),

If you've seen my previous posts you know I was successful in resurrecting my S750 by replacing all the capacitors Lex suggested. Just a couple weeks ago wife and I were sitting on the couch and heard a loud pop. Pulled open the sub and found this:

Before cleaning:


After cleaning:


The capacitor with the missing lead (it exploded clean off) is one of the new ones I had replaced in the first round.

My question is, can I just replace the busted capacitor or do I need to replace that blue thing as well (and if so, what is it)?
Is there enough green landscape to make the repair worth it or will it blow up again?
Is there anything else I should do?

Cheers mates.

So, I know what C62 is as that's one of the capacitors I had to replace before, but I have no clue what to look for with C7, U2 or D26. Can you help me out there?

If I recall correctly, the capacitor he suggested replacing with a high temp ceramic was actually C63 (and I did replace that one with a ceramic) but could do the same with this one if that's likely to be the issue.

Is it even remotely possible that the problem is in the control box and not at the source? Something as simple as whatever is supposed to trigger when you remove the headphones is staying engaged and thus not routing the sound back out to the speakers?

In Post 140 I pasted part of a schematic I found for the S750. I have two other pages in a pdf which I've attached in this post. The schematics specifically state P.S.U. so I don't know if they're helpful for the rest of the board or not (I don't have any electrical experience except for following instructions).  S750PSU_Schematic.pdf ( 105.67k ) Number of downloads: 1166

You're welcome. I actually haven't had time to replace the last blowout, have a new baby in the house that's sucking up most of my free time. However, I was able to find another repository of information on S750 but I haven't had the time to go through it to see if there is anything useful. You can check it out HERE.

Hope it helps! I'll post an update again when I've got my C7 replaced.