Amplifier repair, some pointers please?

[Aragorn]

Hi there,

I've been trying to repair one output on my 2 year old AV Reciever, and i'm hoping someone can provide some assistance in suggesting where to look next.

The unit is an Onkyo TX-SR607, and i discovered a few days ago that the centre channel had stopped working.

I opened it up and traced the signal and ensured the output relays and suchlike were functioning correctly which took me to the power amplifer itself.

The board has test headers on each channel (these can be seen in the schematic below labelled ID), which allow you to measure the voltage across the two output transistors and this can be used to adjust the idle current draw. Checking the working channels showed a voltage of around 10mv, however the centre channel was jumping around between -3mv and +3mv.

Upon closer inspection i discovered some damaged tracks on the PCB near some other transistors, and i repaired these, and now the voltage on the ID header has stabilised and is around 9mv as per the specifications.

However the channel still isnt working. I discovered that if i crank the volume to max, the channel is outputting sound, but at a hugely reduced volume compared with the others.

I suspect therefore that some of the components have become damaged due to the broken tracks and the resulting oddness.

I have a service manual for the amp, and below are some excerpts from the manual showing the schematic for the power amp and its driver stage. The damaged tracks were around Q6042, on the lower right of the "driver" stage schematic.

Power amp:


Driver stage:


I should point out that all the connections on the driver stage diagram are sourced from the multipin connector on the left of the power stage diagram.

Hope someone can assist!

Cheers
Kevin

[sjdemark]

Was the damage to the traces caused by a burn or a cracked PCB?