Hi Dinger,
You are lucky that you found the service manual for your amp, with that it is fully repairable, there is nothing exotic in that amp.
Chances are that some of the final transistors are blown and/or the driver transistors, Q134, Q145, Q235, Q245, and Q134, Q144, Q234, Q244.
Do check the same transistors of the other two channels too!
But do go through the whole amp and check it out.
Use a bench power supply (PS) with current limit for the testing, not a battery! If you do not have a PS like that, use a car battery with some light bulb connected in series with it, it will limit the current if you still have some dead short. Use a car bulb, 12V, about 20W - 30W, the brake lights and directional lights have that rating.
Do check the power supply, that inverter with the MOS-FETs. From the power rating of your amp that inveter provides about +/-30V supply to the amps.
Disconnect the power stage from the inverter (VCC1, VEE1) and see if the inverter works properly.
If I am correct, those PSs with the TL494 IC like to have some load on them to start up and operate, so add a light bulb between VCC1 and VEE1, that is a bout 60V, use 120V incandescent light bulb, 40W or so.
If the inverter does not work, do check the MOS-FETS for shorts, also do check the driver transistors, Q23, Q33. Do look up the data sheet of the TL494, there is lots of info in it about its operation.
If the TL494 is damaged, you can harvest one from an old PC power supply.
A scope would not hurt for debugging.
If the inverter works, you can move on to check the power amps. Here is a good article (and web-site) on how to debug power amps: <http://sound.westhost.com/troubleshooting.htm>
The bottom line is that it is good to check all the transistors in it, as the whole circuit is in overall feed back.
The final amp itself is a LIN-type power amp (just like an op-amp), only difference is that it uses a fully symmetrical input stage. The "Leach-amps" used that topology, you can read about that topology in details here:
<http://users.ece.gatech.edu/~mleach/lowtim/>
Good luck, Peter