XTZ W10.16 subwoofer repair

[mtah]

Hello!

I've had my XTZ W10.16 subwoofer for around 8 years and it has finally given in so I'm looking to try and repair it myself.

A few months ago I started noticing an issue that whenever I turned the sub on, I got a loud buzzing sound that eventually subsided over the course of about 30 seconds. After that the sub functioned normally without problems. Now the problem has gotten worse and the buzzing does not disappear after turning the sub on. Upon turning the subwoofer on, the buzzing starts very loud, and then gets lower in volume until it settles at a constant sound level, but does not disappear which means I cannot use the sub. I've recorded the sound it makes when turning it on and how it progresses to a constant sound level so you can listen to it if you want. The buzzing is unaffected by the volume knob of the amp.

I've taken the sub apart and had a look at the circuit board but cannot find any obvious visible faults. At first I thought it must be the large capacitors of the power supply going bad (despite not showing any swelling or leakage) so I bought two new ones and replaced those. Still the problem remains.

I will upload the sound I previously mentioned along with the schematics of the circuit.

I have a DMM and basic understanding of electronics, though not much experience in repairs.

Any help is appreciated!

Thanks

[Enzo]

When it wakes up buzzing, watch teh speaker cones. Does the cone move one direction and try to stay there? (We are looking for DC on the speaker)

[Jon Snell]

My guess is check/replace C5/6/17/18/122 & C123.

Also, check there is no black goop on the board, that stuff absorbs moisture from the air and can go conductive. All of the Rockit monitors went that way.

[mtah]

When it wakes up buzzing, watch teh speaker cones. Does the cone move one direction and try to stay there? (We are looking for DC on the speaker)

I will check and report back when I get home in a few hours! I guess I can just measure the DC voltage over the positive and negative pin on the speaker?

My guess is check/replace C5/6/17/18/122 & C123.

Also, check there is no black goop on the board, that stuff absorbs moisture from the air and can go conductive. All of the Rockit monitors went that way.

Will do! There is no way to test the capacitors that dosnt require desoldering right?
Also I've checked the board pretty closely for anything out of the ordinairy without finding anything, but I'll have another look at it for black goop just to make sure.

[mtah]

When it wakes up buzzing, watch teh speaker cones. Does the cone move one direction and try to stay there? (We are looking for DC on the speaker)

I've had a look at the cone movement now and it does not seem to have any DC on it, it stays in its central position.

My guess is check/replace C5/6/17/18/122 & C123.

Also, check there is no black goop on the board, that stuff absorbs moisture from the air and can go conductive. All of the Rockit monitors went that way.

I'll upload one picture of the circuit and one close up of one of the circuit board, the black stuff around the edges is not the same goo your're talking about is it?

https://imgur.com/a/UXbe9jw
https://imgur.com/a/0QckzqS

The pictures arent the sharpest.. I'll redo them if it helps.

[Jon Snell]

That RTV sealant used in your amps are slightly better, just for holding the components on the board and stop/reduce vibration.
Not the black goo of death.
Check/replace those capacitors and they cannot be tested on the board so probably, for the price of them, worth just changing them.
Use the same values and voltage ratings but try and find 105° types if possible. That will add to reliability.

[mtah]

That RTV sealant used in your amps are slightly better, just for holding the components on the board and stop/reduce vibration.
Not the black goo of death.
Check/replace those capacitors and they cannot be tested on the board so probably, for the price of them, worth just changing them.
Use the same values and voltage ratings but try and find 105° types if possible. That will add to reliability.

Good to hear, then I dont have to worry about that atleast!

I just noticed there is a capacitor named C5 in both of the schematics files i posted, and they dont seem to refer to the same capacitor. Which schematic are you refering to ASW or GSW?

[Jon Snell]

Good to hear, then I dont have to worry about that atleast!

I just noticed there is a capacitor named C5 in both of the schematics files i posted, and they dont seem to refer to the same capacitor. Which schematic are you refering to ASW or GSW?

C5 on the ASW, the low voltage smoothing capacitor with its partner C6. 1000uF.
C1 & C2 are as important to change; 10000uF at 80volts, the main smoothing capacitor. I have had those go open circuit, especially if from China.

[mtah]

C5 on the ASW, the low voltage smoothing capacitor with its partner C6. 1000uF.
C1 & C2 are as important to change; 10000uF at 80volts, the main smoothing capacitor. I have had those go open circuit, especially if from China.

Thanks for the clarification! The main smoothing capacitors are already replaced as those are the ones I initially suspected to be the problem. I'll get to work on replacing the other caps you recommended in a few days.

Someone also recommended me replacing C14 and C15 on the third pdf. Do you see any point in this?

[Jon Snell]

Thanks for the clarification! The main smoothing capacitors are already replaced as those are the ones I initially suspected to be the problem. I'll get to work on replacing the other caps you recommended in a few days.

Someone also recommended me replacing C14 and C15 on the third pdf. Do you see any point in this?

They are fitted to attemp to stop the regulators from becoming unstable. They would not come under my radar at all. 100n poly caps are extremely reliable.

[mtah]

They are fitted to attemp to stop the regulators from becoming unstable. They would not come under my radar at all. 100n poly caps are extremely reliable.

I see, interesting. I will report back when I've replaced the caps you recommended!

[mtah]

They are fitted to attemp to stop the regulators from becoming unstable. They would not come under my radar at all. 100n poly caps are extremely reliable.

Replacements for the capacitors C5,6,17,18,122,123 are ordered now and should hopefully arrive this week. I desoldered C17 och C18 and was surprised to see that the 10u electrolytic capacitor C17 was mounted AND marked on the PCB with reverse polarity in reference to the schematic. Its positive lead of the cap was connected to the 2.7k resistor. Does polarity not matter with a capacitor this size or why could this be? I guess I will solder back the replacement the same way, and not follow the schematic?

Also, I did a capacitance test on C17 and C18. C17 gave the correct value 10u, but I could not get a proper reading from C18, the reading just went back and forth between Overload and some arbitrairy capacitance number.

Once I get my components I will replace these two caps first and see if that does the trick. Replacing the other caps C5,6,122,123 forces me to cut open the sealant that attaches the foam between the PCB and backplate/heatsink and I'd prefer to avoid that if i can.

[Jon Snell]

If C18 is faulty, that would explain your issues because the amplifier will have trouble settling on a 0volt DC output.
I would say that the positive lead should be connected to the 2.7k resistor as it is more likely there could be a DC offset voltage on the input rather than on R2.
One capacitor at fault ... change the rest is my advice. RTV sealant is cheap to replace.

[mtah]

If C18 is faulty, that would explain your issues because the amplifier will have trouble settling on a 0volt DC output.
I would say that the positive lead should be connected to the 2.7k resistor as it is more likely there could be a DC offset voltage on the input rather than on R2.
One capacitor at fault ... change the rest is my advice. RTV sealant is cheap to replace.

Great! Cant wait to get the components now and see if it works and I'll make sure to replace all of 'em at once.

For the RTV sealant, can I just use normal white silicone sealant that one would use in a bathroom?

[Jon Snell]

I wouldn't as bathroom sealant is vinegar based to cure it.
I use https://www.ebay.co.uk/itm/164510389...AAAOSwGb9froLt
it is cheap and works well, plus it is non porous.