Behringer GMX212 PS ?

[gtrplayr1976]

Hey folks,

Does anyone know what voltages are on the transformer secondaries, and on the PS out to CB with speaker outputs ( Red, Blue ,Black) ?
This amp will power up , but theres nothing coming through the speakers.

Here's what I read on the secondary disconnected from PS board ,one lead to ground -
o=16.2 vac , brn= .4, o=15.6
Y=40.3 , Brn= 15.8, Y= 7.9
i didn't check the two gray wires

Thanks all.

[Enzo]

Without me looking, the amp runs on positive and negative supplies for the power amp, and then also +/-15v for the preamp. What voltages are present on the Power AMP leads? Chances are they will either be missing or correct. The schematics don't specify voltages anyway, as is often the case in amplifiers.

Test the two speakers, are both OK?

PLug the guitar into the "Slave In" jack for each side. ANy sound that way? If so, the power amps work, and if not, either BOTH 3886s are blown, or the mute circuit is stuck on.

[gtrplayr1976]

Thanks Enzo. I added some voltages I took off the xfmr.

[gtrplayr1976]

ok...so no sound through the Slave In jacks. How would I check to see if it's stuck in mute ?


Thanks

[Enzo]

Not usually a transformer fault, what DC voltages are feeding to the power amp?

And you can't disconnect the secondary from the board and then measure voltages to ground from it. There is a 6 pin connector, X3, and pins 2 and 5 are the center taps for the two windings, so the only meaningful readings would be from 2 to 1 and 3, and 5 to 4 and 6. But if there is good DC< then don't bother.

If there is no good positive and negative power rails, the power amps can;t work.

Did you test the speakers themselves?


Mute? Look up the data sheet for the LM3886. There needs to be at least half a milliamp of negative current flowing into pin 8.

But find out if the main DC supplies are getting there. Pins 1 and 4 are the main power pins on those ICs. BE CAREFUL. If your meter probe slips and shorts a power pin to some other pin, you can destroy the IC in an instant.

[gtrplayr1976]

I'll check these out . Thanks Enzo

[gtrplayr1976]

Not usually a transformer fault, what DC voltages are feeding to the power amp?

And you can't disconnect the secondary from the board and then measure voltages to ground from it. There is a 6 pin connector, X3, and pins 2 and 5 are the center taps for the two windings, so the only meaningful readings would be from 2 to 1 and 3, and 5 to 4 and 6. But if there is good DC< then don't bother.

If there is no good positive and negative power rails, the power amps can;t work.

Did you test the speakers themselves?


Mute? Look up the data sheet for the LM3886. There needs to be at least half a milliamp of negative current flowing into pin 8.

But find out if the main DC supplies are getting there. Pins 1 and 4 are the main power pins on those ICs. BE CAREFUL. If your meter probe slips and shorts a power pin to some other pin, you can destroy the IC in an instant.

I really didn't see any voltage on X3, but on one of the LM3886s pin 1 to 4 was about 75vdc. It's really hard to get to the other one.

I checked the speakers with a multi meter and both read 5-6 ohms

How would you read the ma on pin 8 ? from pin 8 to ?

Thanks,

[Enzo]

Is there any negative voltage on pin 8?

Can I assume you have the power amp assembly loose from the chassis? Getting at all the pins on the 3886s might be hard, but flip the thing over, and the main filter cap terminals ought to be easy to get at. ANd the underside of the 3886s will be easier to take voltage readings at.

[gtrplayr1976]

Is there any negative voltage on pin 8?

Can I assume you have the power amp assembly loose from the chassis? Getting at all the pins on the 3886s might be hard, but flip the thing over, and the main filter cap terminals ought to be easy to get at. ANd the underside of the 3886s will be easier to take voltage readings at.

From pin 8 to ?

I have not taken the power amp out , but I will ,and see if I can get to both ICs. Does the 75v between 1 and 4 seem normal ?

[Enzo]

Oh, 75v BETWEEN 1 and 4. Sure that sounds OK. That would mean 35v or so for each power supply.

DC voltages with respect to ground unless otherwise noted.

[gtrplayr1976]

Does the heatsink need to be removed with the power amp?

The one IC I can get to shows some varying dc voltage on pin 8.

[Enzo]

I don;t remember what power amp is in there. Ins;t it a sort of heat sink with a fan on the end sitting on a circuit board slightly larger than the heat sink? If not, how about a picture?

The two ICs have their pin 8s wired together, so whatever is on one should be on the other.

[gtrplayr1976]

the heatsink is mounted on the bottom of the chassis ,and is about 10"x5"

[gtrplayr1976]

So Enzo...if the mute is stuck on...what then? Is there a voltage at the speakers ?


Thanks, Tom

[Enzo]

It is a mute. If it is stuck on, the amp stays muted. That means it makes no sound.