Hafler P300 weak channel

[Axtman]

I have a Hafler P300 PA amplifier that I am working on for a friend. He bought it at a thrift store and is planning to flip it.

I tested the amp out and Channel 1 works fine (with a very slight crossover distortion notch in the sine wave). Channel 2 produces a very weak soutput signal and does not increase very much with the volume control.

I am hoping that someone has experience with this amp and problem.

Service Manual: P3000.pdf

[g1]

A good place to start would be checking that you have equal signal level coming out of both volume controls.

[x-pro]

maybe it's set in bridge mode ?

[The Dude]

Certainly worth checking, but in bridge mode, the two channels would be out of phase yet still each producing the same output level. I don't think it would cause the symptoms described.

[x-pro]

maybe it's set in bridge mode ?

The schematic tells us that there is no switch to bridge mode.

So, the schematic is given only for 1 channel, so we will be guided by it.

To start by measuring all power supply voltages, both power amplifier and chip power.
Then, apply a balanced signal to the channel 2 input and check its presence on pins 1 and 7 of U1.
SW1 in STEREO position.
Do not connect any load to the amplifier output.