Behringer Eurolive B205D

[Enzo]

So the power amp seems able to make some sort of sound, but no signal leaves the preamp.

That leads me to re-ask if there is proper power supply at the ICs on the preamp.

You mention no signal at pin 7 in channel 3. You have two other input channels, is there signal present at the output of either of those when input to? That would be pin 14 or IC6 and IC7.

If all three channels make no output, then I stress that power supply is critical. And by no output, I mean right at the circuit, not the speaker. If those channels do work, then something in common to them all is involved. All the circuitry upper right on page 1 of the schematic.

[techie]

IC1 ( 7815 ), IC2 ( 7915 ) and IC3 (OP1 ), voltages.

[techie]

Thank You Sir.

[The Dude]

IC2 (7915) is a -15V regulator. This is your negative supply to the op amps. You have -23.7V in, but no -15V output. Either the regulator is bad, or there is a short on the -15V line. I would start by changing the regulator. If you still have no -15V, you likely have a short on the -15V line. Given that you have a positive voltage there, it could be that an op amp is "leaking" positive rail to negative rail.

[techie]

Thank You Sir.

[techie]

I replaced D3, D4 ( which were shorted ), these are connected to X10 5P ( FROM_REAR ) and R15, R17 and IC2B, still no change in -Vcc = +1.6v

When I disconnect X12 4P connector ( which connects to the Power Supply Board ) from the Pre Amp circuit board the connector has Vcc Red = +14.8v, and -Vcc Brown = - 15.2v.

When I re-connect X12 4P connector to the Pre Amp circuit board Vcc = +14.8 and -Vcc = +1.6v.

Removing X10 5P and /or X11 3P has no effect on the Vcc = +14.8 and -Vcc = +1.6v

[Jazz P Bass]

Quote:"When I re-connect X12 4P connector to the Pre Amp circuit board Vcc = +14.8 and -Vcc = +1.6v."

Something on that board is loading down your -15V rail.

[techie]

Do you have any idea what kind of short would give this -Vcc = +1.6v?
Diodes?
Op-Amp?

Thank You.

[g1]

As it is actually going positive, I would suspect something that is connected to both the + and - supplies, like an op amp.
Feel around for any hot ones.

[techie]

Thank you Sirs!

[Enzo]

Fell all the op amps with your fingertip. ANy getting hot?

[techie]

There is nothing over-heating on the pre-amp board ( op amps , diodes, transistors, etc) .
I do have C48 testing short.
I removed C48 and the C48 circuit pads test short.
C48 is to the left of Pin 1 of IC1 and is connected to X11 3P, Pin2 (BLK ).
The schematic has C48 connected between X4 ( power amp ) and X16 but I do not see X16 on the schematic.

[Enzo]

Took me forever to spot C48. next time maybe some clues as to where to look. Lower left of page 1. X16 might be a ground wire. The cap looks to me like it connects sub-grounds together, and so would measure shorted.

[techie]

There are no overheating components.
I have disconnected pin 4 ( -Vcc = -15v ) from op amp IC's 1, 2, 3, and 5, individually and all at once hoping this would show a short in one of those op amps,
the result was no change in the -Vcc = +1.6v.

[The Dude]

If you look at the first page of the schematic, in the lower right it shows where +-15 goes to the IC's, you should check/unsolder all of those pins. Also, IC4 isn't shown on that part of the diagram, but it is the same pins as IC6&7. It's never fun tracking down a rail short. Sometimes you get lucky and it's the first thing you try. Sometimes it might be the last connection on the board. You just have to be thorough and look at all parts that have both rails connected.