Behringer BX1800 Power Supply Issue

[misterc57]

I have a BX1800 that does not seem to be sending the +15V positive rail to the pre-amp board. The -15V is there. There is a 4 wire jumper from the PS board to the preamp board. I believe the 4 connections are +15B, -15V, output, ground.

It looks like the PS board has been worked on before. The two large white 5 watt resistors (R4, R5) were both loose and I reflowed them. One of the traces is lifted so installed a jumper wire.

The schematic I have attached seems to be the correct layout but the component references on the power supply board do not seem to match.

There are two power transistors. T4 - MJE340 and T5 - MJE350. Schematic shows 7815, 1915. Might the MJE be replacements?

MJE350
B = - 35 V
C = - 10 V
E = - 10 V

MJE340 has negative voltages at the C and E. Does not seem right to me.
B = + 40 V
C = - 5.2 V
E = - 5.8 V

Is this a problem with the MJE340 or are other problems causing the negative readings?

Thank you, MC

Behringer-BX-1800-Preamplifier-Schematics.pdf

[Enzo]

The 340 and the 350 are not voltage regulators, they are transistors and are the drivers for the output MOSFETs. If you are referring to the transistors on either side of the two large filter caps. I can see on the board the silk screen even says 340 and 350 next to them. And schematic calls for T4, T5 to be them.

7815 and 7915 are voltage regulator ICs and are marked on the schematic as ICs. They ar IC2 and IC3 on the drawing, and I expect them to be on the heat sink. And likely 7815/7915 will be silkscreened on the board next to them.

Is your power amp the LPA1180?

One of the two power resistors appears to have a wire coming through the board, but I don't see it soldered to anything. And if the end of the resistor is not connected, that will kill one of the 15v supplies.

[misterc57]

Yes Enzo. That was the problem. Working now.

Thank you

[Enzo]

Hey, glad it worked out.