without touching anything today I connected and I've noticed that a speaker only works if I connect to the connection center.The speakers only sound in the central connection, but heard very low and distorted.¿ you think you can be ? . I have other speakers and I can assure you it works perfect.what worries me most is that the sub is still not working.Why the sub does not work? Do you not supposed power is coming?

I tried to control with mute button and still not working

Do you have another device such as a dvd play that you can use to provide input to the subwoofer? Since the subwoofer output comes directly from the Bash amps you should get audio if it is working properly

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

Hi, Thanks for the info. The one you posted in 140 is included again in your recent post and all of them together are for the Power Supply board (PSU) but what is needed is a schematic for the amp boards (the 2 amp boards are identical), and the two output boards which are sandwiched together. I did get some good schematics for the Bash sta575 power amplifiers, these are the 27 pin IC's on both amp boards which the red/black wires connect to the subwoofer and the rest of the speakers outputs. There are 4 small output capacitors connected to each output configuration but it would be very difficult to replace them all because of the limited space on the boards. However, the glue is pure white and I don't think they are a problem. If there was a problem with one particular speaker, it might be worth while to change them out. BTW how did you make out with your problem with the burned out capacitor? Were you able to clean it up and replace the components? I believe you were looking for C7 replacement. I just order a couple of those safety capacitors (the blue ones) if you need the info on ordering them. As with most electronics, experience is important, especially safety precautions, but if you were able to follow Lex's instructions and replace all those caps, I believe you did very well. It is most import that you do it safely of course, but with particular attention to the details of mounting techniques, and maintaining everything exactly how it was intended and not disturbing other stuff. The caps and diodes must always be mounted with respect to the correct polarity (+, -) as indicated on the board, or something may blow or burn up, and a short can occur by just dropping a speck of solder in the wrong place. Thanks for your help, but we may have to struggle with what we have, even though its a bit difficult to read the traces on those other boards especially since they are double sided, but it can be done.

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.

hi , please check this video . ( I replace 4 CAP on Power Supply board 470uf 250v ) I get my amp to turn on again but I want to know
its still power supply board problem or other problem this video will show u how amp works .
the headphone output of the console is working well but output channels for speakers even subwoofer is not working well
sound is very low and noisy . some channels don't have sound at all .

https://youtu.be/4tFY61IPh-w

Welcome jviojtaba to the study of the 750 speaker and it's repair group. I watched and listened to your video, and I congratulate you on getting power back to your system. However, if you have not read the previous ten pages on this subject, I recommend that you do so as it will save us from having to explain the many details and nuances of this project. If your system has never been opened or repaired previously you will need to do some basic housekeeping. Specifically, you will need to remove all degraded glue from the main power board and replace all of the remaining original electrolytic capacitors on the main board. The details on how to do this is contained in the previous pages, including the type of caps you should used as replacements. Until that is done, it will be nearly impossible to determine what may be causing your problem, not to mention that the potential for additional problems will still exist. It helps to have knowledge of electronics, but so far we have only been able to find schematics for the power supply and none for the amplifier boards which requires at least some background in how amplifiers work. I have made good progress in restoring the main power supply board, but I am still dealing with a high pitch squeal coming from the sub woofer, and I probably will begin replacing some caps on the amp boards, although they are not surrounded by degraded glue, but are likely to cause problems. Good luck, and let us know here how you are doing and if we can be of any help.

Is exactly what happens to mine.

Ricter, I'm back and have not given up, just had other issues. Will let you know what I find out

thx friend

I have the same problem!
For what I could figure out so far, the problem is in both the 70v output from PSU.
There seams to be short-circuit on these lines. Maybe the FETs... Haven't had time to check...

I will give my s750 amp to some electrical professional but 1 person I go to him said Its really time killing and he said its will take a lot of time to
find the problem and fix it and maybe some of chips are damaged and there is no replacement for them too , anyway if u still thinking this is because
of power supply board I will tell the repairer man only change the CAP'S and nothing else if that's works I will be so happy .
anyway I live in Iran and that's the biggest problem here Its hard to find good electric professional here .

so what did u done for ur amp ? did u change all cap's and clear the glue ? I want to know what else I can do for mine too and I will share it here and maybe help u too .

I really hope someone can help me.

After a power outage my S750's stopped working. I thought it was the fuse, so I bought new ones and replaced it, but it didn't work.

It took me a while to find a place that can repair speakers and they told me the IC's blew up etc etc... I was excited it was gonna get fixed.

After a week or so I got my speakers back and they did work. But there was a problem... I don't know how to explain it so I asked around and a few people told me the term is "humming". Forgive me if its the wrong term, but this is what happens... there is a high pitched annoying sound that comes from the sub-woofer. After the repair it continued for around 20 to 30 mins and stopped. I thought it was fine then, but the next day I switched it on again and the sound was back... again for 20 to 30 mins. I've noticed that if i keep the sub-woofer on the annoying sound stops but when I switch it off for a few hours it comes back for 20 to 30 mins.

Can somebody please tell me what the problem is and how it can be fixed?

Any help from this community will be much appreciated.

Thank you in advance.

Looking forward to some positive replies.

--content deleted, using another account to post. this account is from a friend--
ok, it seems that another account has problem to post (no one else can see my post except myself), so I post it back here.

Thanks for sharing the repair experience.


2015-04-23 Update
Damn, I use a flat knife opened the back iron plate, but, I can't open it more, only 5cm: there are wires connected to the subwoofer, I can't see inside how to detach it. Seriously, 5cm, and lots of stuffs blocked the view. I can't even put hand into it.

So how do you guys disassemble it? Can you put your back iron plate down after screw down?

@lex @dlduscg @richer , please help me


2015-04-27 Update
-- Thanks again, now, I had disassembled the the back iron plate, the 3 connectors of the woofer are actually facing inside of the box, so it makes the wire shorter



And 3 bulged capacitors: one CapXon (68μF 450V 105°C), two JunFu (1000μF 100V 105°C, like this one http://forum.lowyat.net/uploads/attach-11/...-1372785951.jpg , @lex does not replace this one because they are not bulged )







This post has been edited by asenrzhang: Apr 27 2015, 07:11 AM

To everyone having the typical problems with the Gigaworks S750 I suggest that you work on the main power supply first, and if it has not been worked on before I recommend that you start by replacing all electrolytic capacitors, then clean up the degraded (darker colored) glue as described in the previous posts. Schematics for the main PSU are available to help with this part. When that is done and you can see any other obvious indications of burnt, cracked, broken, or otherwise suspicious components, that is where you begin the process of restoration. When you are sure there is no more visible or outward damage, and everything has been properly reconnected you can consider applying the power. When the green light comes on and stays lit without any other problems, you can proceed to checking out the outputs. It has been my experience that when you get to this stage, and you have some or most of the speakers back, you will likely be looking for a bad amp output (Bash STA575). There are no specific schematics for the amp boards that I know of, but you can get detailed information about the amplifier stages by tracing the output wiring and getting data info on the Bash amps or other individual components online to help understand how the amps work and to isolate the possible defective amplifier. I would not be concerned about all white appearing glue because it is not likely to be a problem and the less you disturb things the better you will be when retracing your own tracks. I hope this has been helpful. There are some good inexpensive digital multimeters available online that can help you find defective components to assist you in the process of determining which components to replace. They include checking resistors, capacitors, diodes, transistors, as well as the current and voltage without removing them from the circuits in some cases as well. Good luck. If I find out anything new I will post it here.

Hi, I have a problem with my S750 set too. Please help

I removed almost all the glue from the main power board (biggest board), but still have following issues:
1. Plug-in all three ribbon cable and the green light is blinking continuesly
2. Remove those 2 green ribbon cables the green light blinking like 3 times and steady, I can even use the remote to power it on, but of course no sound.
3. Plug the gray and one of green ribbon cables SOMETIME (you may call it luck) the green light blinking like 8-10 times and then steady.
4. No visible physical damage can be seen with my noobs eyes.

Each time the green light steady I can use the remote.

Based on that symptoms, what to do with the set?

Very appreciate for your help.

Enha - Jakarta

This post has been edited by MasEnha: Jun 13 2015, 05:27 PM

[quote=MasEnha,Jun 13 2015, 05:24 PM]
Hi, I have a problem with my S750 set too. Please help

You did not say if you replaced any of the electrolytic capacitors...if you did not, then that is where you must start

[quote=dlduscg,Jun 14 2015, 12:12 AM]
[quote=MasEnha,Jun 13 2015, 05:24 PM]
Hi, I have a problem with my S750 set too. Please help

You did not say if you replaced any of the electrolytic capacitors...if you did not, then that is where you must start

[/quote]

In addition, but before you replace the caps, check each connector, including the main power connector for a bad connection. That may solve the problem, but you will also need to replace the caps