Mackie SRM450V2 no Bass

[guitardad]

Took in a pair of Mackie SRM450v2 on consignment. One was no HF out (TDA IC bad) and the other came in dead. Found the usual suspects in the SMPS. After that was restored, found there is no LF output, but the hf driver works fine, signal indicators are all good too. LF Driver tested fine, and the rails (+/- 75v) to Q11 and 12 semi's are also ok.

What I am not figuring out is IC U28 Lo / Hi Driver for this.

V1 and V2 of this 450 series sure changed..... what's different to me are their choice of commons. In that LF stage it indicates common, earth (chassis), and what looks like.. hot or live ground.

Even with an iso transformer in my variac I have not scoped this circuit as of yet.

Anyone worked on these? Any pointers? Is there a block diagram (for the amp/servo etc)?

Thanks in advance.

[diydidi]

hi, could you please post schematic...

[guitardad]

hi, could you please post schematic...

See attached