Need schematic for this board

Hi. I've got this old power amplifier and this stepper driver board is broken. Maybe some of you have the schematic diagram of this (with the value of parts included if possible). It uses LM311 IC. A link to where I can purchase the whole board will be appreciated as well. Thanks
 

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A technician could easily test the parts and replace bad ones, if any.
However, parts on the main board could also be bad (power transistors, etc.).
Do you have duplicate daughter boards to swap and check?
Are you sure the software is not the problem?
 
The transistor Q7 (upper right corner of your photo) looks damaged. I believe it's marked G1 like the others in the corners, which makes it an MMBT5551. See attached data sheet.
Also the trace that goes from pin 1 of U4 and under D7 and out to the header pin also looks damaged.
What amp is it?
The soldering cetainly does not look very good, which could be part of the problem as well.
 

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