I have been in that repair/service business for over 30 years. These amps are repairable. I suggest you get a good service manual for them before you start!
Make sure you check every part in the power and driver section and replace any with equal or better rating. To check the power transistors - you have to remove them all out of circuit since they are all in parallel. One bad or leaky transistor will show a short on all of them even if the rest are good. I tell you - for me that was always a sweaty affair...... after having replaced what I could find and then switching it on. If you missed, leave one 2 cent diode in there which is shorted, you may blow the whole thing again.
Never hook up a load when you have replaced all the bad parts - do that later once the amp does not blow any more fuses and/or has no DC offset at any output. That can be trimmed usually. Check the voltage across all the .22Ohm current limiting resistors for each bank of power transistors... these are the ceramic type of 5Watt or so rating. It is advisable to start up the amp with a variac and slowly bring up the line voltage while monitoring the outputs for DC offset.
These amplifiers usually have a speaker disconnect relay built in to protect the speakers from being fried on case you have either the full positive or negative supply rail voltage present due to some short somewhere. Therefore you should measure the output before the relay at the junction between the ceramic current limiting resistors which is the actual output routed to the relay.
It is highly unlikely that both sides are blown. If one is good, make cold comparative measurements with the power off. You may also have to disconnect the B+ and B- from the board to do that.
These amps having the fault light on usually means at least one side has an offset at the output and triggered the disconnect relay to the speakers. Make sure you lift out all the power Xtors one after the other and mark them where they were and check them each out of circuit for any leakages and/or shorts!
I wish you luck!