Behringer cheap mixer powers up then shuts down

[fjgaston]

Hi,
I use a small cheap mixer called Behringer XENYX 802 when playing gigs in pubs.
Last Thursday, it stopped working. When I plug the psu, it just power up then shuts down after 1 or 2 minutes. (power led is still on but very slightly)
I've read in other topics that it could be because of the voltage regulators (7915 and 7815) The outuput of both regulators show -15v and +15v then +0.6v and -1v when it "shuts down" does it mean that I have to change them or could it be something else ?
I only have a multimetre (no oscilloscope).

 

[audiomixer]

you might want to check if the regulators go hot and then go in protection mode due to a failure downstream. I am thinking of excessive power draw and then shutdown. do they get hot at all?

try measure the amps drawn just after the regulator (you might have to desolder the output led)

- michael

 

[fjgaston]

The regulators are hot, yes.

Do you mean desoldering the regulator to measure current on the output ?

 

[JohnRoberts]

Regulators routinely run hot, but if they are shutting down due to overheating, there will be other hot components in the mixer to maybe feel around (with the mixer unplugged) for where the excessive current is going.

JR

 

[joaquins]

Get a more expensive one, they fail less often  In the mean time let's fix this one that's more fun and cheaper than getting a new one! (just kidding, only true is about fixin' this one)

Does the PS fail even when the mixer isn't plugged??
Maybe the PS just suffered for some reason and there's nothing wrong with the mixer, just the PS (a short on the output when unplugged from the mixer but plugged to the wall ¿?) If this is the case you just need to repair the PS. Behringer's ADA8000 is known for failing regulators, overheat because too much power for no heat sink at all, linear, same transformer for 220V and 240V, in 220V mains it runs hot (my case) in 240V they run hot for a while and then they start to run cool, very cool 


Do you have a bench PS? I'd try powering the mixer with one (limiting the current) to see if it's over specs. Maybe the mixer has something wrong that makes the PS to shut down to prevent damages (over current or over temp protections on the regulator) in which case the PS is fine and the mixer is bad.

The third option is both fails independently because the fail in one of them broke the other (let's wish this isn't the case)

Good luck!

JS

 

[fjgaston]

Hi, thank you for your answers.
I don't think there is any other componant on the mixer that gets hot except from the 2 regulators (and they are screwed to a very small heatsink)

I'm considering buying another mixer but I already have other mixers, a 48 track and a 24 tracks but this one has the avantage of being small, and I'll try to fix it if I can.

I just measured voltage at the PS (MXLU3)
The PS says :
OUTPUT : 2*18.5V~ /2*250 mA
I measured :
40.1 V AC between pin 1 and pin 3 ... but I don't get anything between pin 2 and any other pin.

 

[JohnRoberts]

Hi, thank you for your answers.
I don't think there is any other componant on the mixer that gets hot except from the 2 regulators (and they are screwed to a very small heatsink)

That does not compute... if the regulators are getting hot they a delivering even more power to the load.

I'm considering buying another mixer but I already have other mixers, a 48 track and a 24 tracks but this one has the avantage of being small, and I'll try to fix it if I can.

I just measured voltage at the PS (MXLU3)
The PS says :
OUTPUT : 2*18.5V~ /2*250 mA
I measured :
40.1 V AC between pin 1 and pin 3 ... but I don't get anything between pin 2 and any other pin.

You could get a higher current PS and just run it until the fault catches fire (kidding).

Carefully probe around with your finger to find where the fault current is going, because that current times PS voltage will make watts of heat.

JR

 

[bruno2000]

.........because that current times PS voltage will make watts of heat.

Is that an Elmer Fudd quote?
Best,
Bruno2000

 

[Andy Peters]

.........because that current times PS voltage will make watts of heat.

Is that an Elmer Fudd quote?

something I saw on the Internet last week (can't remember where):

Elmer
Fudd
Paternity
Suit

 

[walter]

That mixer uses a wall wart power supply. From what you describe, it sounds like the power supply is working, 40v across two pins for a +-18v.  prove it- take the mixer to guitar center without the power supply and ask to try one of their power supplies, If it works, get a new psu, $15.00 ebay. If it doesn't work you could try to fix the mixer.  When you power it on and it shuts down, measure voltages on an op-amp for example, you should have a positive and a negative voltage somewhere. If one of those is missing, that could indicate a bad component.  You can feel a bad op-amp get hot, you can see it with frosty freeze spray.

 

[PRR]

> 40.1 V AC between pin 1 and pin 3 ... but I don't get anything between pin 2 and any other pin.

Sounds like a 37V AC center-tap winding where the center-tap has gone missing (wire broke, disconnected, etc).

It may "center" at turn-on because it feeds two equal caps.

But the caps won't hold equality forever, and probably not for long.

Without the CT, the "+ and -" rails won't balance, the power supply gets off-center. Audio paths may mis-bias enough to pass "no" signal". If LED is on one rail (typical) then it goes bright or dim depending which way everything slides. And at some point the 60V DC into "35V" regulator may cause a regulator shut-down (and then burn-up).

Opening wall-warts is dangerous (both shock and sharp tools) and often futile. If the replacement is $15, just buy one.

 

[Whoops]

That mixer uses a wall wart power supply. From what you describe, it sounds like the power supply is working, 40v across two pins for a +-18v.  prove it- take the mixer to guitar center without the power supply and ask to try one of their power supplies, If it works, get a new psu, $15.00 ebay. If it doesn't work you could try to fix the mixer.  When you power it on and it shuts down, measure voltages on an op-amp for example, you should have a positive and a negative voltage somewhere. If one of those is missing, that could indicate a bad component.  You can feel a bad op-amp get hot, you can see it with frosty freeze spray.

1) "take the mixer to guitar center without the power supply and ask to try one of their power supplies, If it works, get a new psu"
Yes, I would advise the same, I think the fault is in the PSU.  Try another PSU with your desk

2) Are the regulators on the wall-art or inside the Desk? I remebered now that maybe the wall-art just has the transformer and that the PSU part might be inside the desk. Anyway I would replace all the Electrolytic Capacitors on the PSU and also all the regulators. They're all cheap components so it's better to replace them all. And then Try again, is it working now?