M-Audio GSR18 speaker, powers on but no sound.

[Xandros]

This is a big powered sub, it appears to power on ok (lights come on) but there's no sound from the speaker, not even crackling/pops/hissing. I took the actual speaker out and tested it passively using another amp and it did output music I played (all be it very quietly but as I say I only tested it passively) so that seems to work.

The sub has been used outside a lot and it seems to have been stored in somewhat cold/damn conditions. When I took the circuitry out to have a look I could see straight away there's lots of corrosion on many of the metallic parts and around some solder joints and there's some sort of residue (likely from damp) in places on the PCB.

The caps all look sort of ok I guess, no apparent leaking or bulging, except perhaps for one of the big ones (bottom left in the third picture). It does look ever so slightly bulged but I can't really tell if actually is or if it's just my eyes playing tricks. And there's a small one not far from it that looks a bit suspect (4th picture). Beyond testing voltages I can't do anything else (no oscilloscope) so I post here on the off-chance any of you pros could shed some light on it.

I haven't had any luck locating a schematic for the thing either. M-Audio haven't made these speakers for years apparently.

Thanks in advance!

[Khron]

Re: M-Audio GSR18 speaker, powers on but no sound.

If you don't have an oscilloscope available, do you have any (other) test equipment?

[Xandros]

Re: M-Audio GSR18 speaker, powers on but no sound.

Only a multimeter. It has a few useful capabilities but it's nothing special.

To be honest I was hoping for an easy fix, like I'd pull the board out and see something obviously wrong with it such as an exploded/leaking/buldged cap or two or perhaps broken solder joints that I could easily touch up but beyond the corrosion there doesn't seem to be anything visibly wrong with it. I knew right from the start if it was anything more complex wrong with it I was going to be out of my depth. Total hobbyist here you see.

[petehall347]

Re: M-Audio GSR18 speaker, powers on but no sound.

do you hear the relay click ?
you can build a signal tracer with a .01uf capacitor and use your working amp to listen .

[Xandros]

Re: M-Audio GSR18 speaker, powers on but no sound.

I don't hear anything when I power it on, no clicks or buzzing or... Well anything. Also I can't use the other amp though, it was just a small thing from a stereo we used to test the speaker that wasn't mine and I no longer have access to it (not for a good few weeks anyway).

[budm]

Re: M-Audio GSR18 speaker, powers on but no sound.

https://www.badcaps.net/forum/attach...0&d=1491561338
It looks like one of the transistor pin (next to c73) is not soldered proeprly, some for the one next to c69 (I know it is double-sided board so it may make contact on the bottom side). So you should look really close at the boards.
I also need good straight shot of the top and bottom side of the board to see how the power relay is driven.

[petehall347]

Re: M-Audio GSR18 speaker, powers on but no sound.

pic 2 ..
q1 looks strange and what is that above it ?
d6 looks wonky but might be ok .
also see some solder joints that might be bad .
i also noticed the big transistors arent sitting flat on the heatsink .pic 6

[Xandros]

Re: M-Audio GSR18 speaker, powers on but no sound.

https://www.badcaps.net/forum/attach...0&d=1491561338
It looks like one of the transistor pin (next to c73) is not soldered proeprly, some for the one next to c69 (I know it is double-sided board so it may make contact on the bottom side). So you should look really close at the boards.
I also need good straight shot of the top and bottom side of the board to see how the power relay is driven.

Good spot, they do seem soldered properly on the underside though;



Here's as best shot I can get with my phone camera top and bottom of both boards with a couple of closeups:

pic 2 ..
q1 looks strange and what is that above it ?

Not sure. There are a few splodges similar to it dotted across the board, it seemed to wipe off and didn't appear to be damage to the PCB under it. A not so focused closeup:



There's this weird splodge too on the other board;

d6 looks wonky but might be ok .
also see some solder joints that might be bad .
i also noticed the big transistors arent sitting flat on the heatsink .pic 6

Yea any unsoldered spots I'd seen seem to be soldered on the underside OK. Also with the big transistors I think that's just because I'd already unscrewed the clamps that were holding it down as I'd already looked at the underside of the board so it wasn't sitting flush when I took those pictures.

[budm]

Re: M-Audio GSR18 speaker, powers on but no sound.

I will give test points once I look at all the pictures.
Looking at the bottom side of the power supply/power amp board, that black power relay should come on when the unit detects the incoming audio otherwise it will stay in standby mode so the power supply is running at very low level until the relay is turned on.
So for sure you do not hear any clicking sound coming from the relay?
This is going br tough to trace because it is double-sided board.

[Xandros]

Re: M-Audio GSR18 speaker, powers on but no sound.

So for sure you do not hear any clicking sound coming from the relay?

Not a thing, even with audio being piped into one of it's two inputs it just sits there quiet as a mouse.

[budm]

Re: M-Audio GSR18 speaker, powers on but no sound.

https://www.badcaps.net/forum/attach...6&d=1491649247
See that U3 (not used) is ? Check the DCV between cold side GND and Pin 4, cold side GND and pin 8 to see what you have.
BTW, you know how to count the pins of the IC, right?

[Xandros]

Re: M-Audio GSR18 speaker, powers on but no sound.

https://www.badcaps.net/forum/attach...6&d=1491649247
See that U3 (not used) is ? Check the DCV between cold side GND and Pin 4, cold side GND and pin 8 to see what you have.
BTW, you know how to count the pins of the IC, right?

I think so but just to be sure; I looked at the IC next to it which has a stripe on one side as do the other chips in the vicinity and based the pin layout on them.



That right?

[budm]

Re: M-Audio GSR18 speaker, powers on but no sound.

That is correct pinout for the IC.

[Xandros]

Re: M-Audio GSR18 speaker, powers on but no sound.

pin 4 seemed to hover around 1.03v, pin 8 hovered around 0.61v

[budm]

Re: M-Audio GSR18 speaker, powers on but no sound.

pin 4 seemed to hover around 1.03v, pin 8 hovered around 0.61v

You are sure that meter is good? What did you use for GND ref. point?
If it is, then those OPAmp ICs are not getting the +/- DCV run.

[Xandros]

Re: M-Audio GSR18 speaker, powers on but no sound.

Yea I must have done something wrong. I just did it again, now both pins are reading 2.6v or there abouts.

Sorry about that! Not sure if that makes any difference though, but anyway I guess before with the other readings I must have knocked the meter onto a different range or something. This time I made sure it was on dcv autorange and just let it do its thing. As for the ground, I'm using the earth wire as cold ground, presumed that was right since it's attached to one of the screwholes/chassis.

[budm]

Re: M-Audio GSR18 speaker, powers on but no sound.

Check the resistance between pin 1 and GND, pin 2 and GND on the input board.
Check the DCV between the two legs of each one of those two caps (marked in the picture) on the power supply/Amplifier board.

[budm]

Re: M-Audio GSR18 speaker, powers on but no sound.

Yea I must have done something wrong. I just did it again, now both pins are reading 2.6v or there abouts.

Sorry about that! Not sure if that makes any difference though, but anyway I guess before with the other readings I must have knocked the meter onto a different range or something. This time I made sure it was on dcv autorange and just let it do its thing. As for the ground, I'm using the earth wire as cold ground, presumed that was right since it's attached to one of the screwholes/chassis.

I expect about 12~15VDC.
See post 17.

[Xandros]

Re: M-Audio GSR18 speaker, powers on but no sound.

Hello, sorry for the extremely late reply. I went on holiday around Easter and have been really busy since I got back and sorting this thing out has been an afterthought. But anyway I got around to testing the resistance today and it just keeps reading OL on those pins and gnd. Didn't bother with the caps yet.

Unless OL was an expected result, then I think you may be right and my meter's kaput. Yet another thing goes wrong when I'm trying to fix something else. Story of my life that is.

[Xandros]

Re: M-Audio GSR18 speaker, powers on but no sound.

OK so, after another lengthy absence I've finally done the tests you suggested.

Resistance between pin 1 and gnd is 3.270kΩ and pin 2 and gnd is 2.950kΩ

I tested the voltage of those caps, one reads aprox 20v the other is approx 19v.

Cheers.