Hi All,
Barrie, I'm going to let Shannon take this one, as it's his baby, but I just want you not to get too discouraged with the DC resistance measurements you got on the power transformer. Alternating current is interesting stuff; what would appear to be a dead short when measuring with an ohmmeter could actually have several (or even dozens) ohms impedance when measured at 50 or 60 cycles, or Hertz.
One quick and inexpensive test you can make requires a 15 or 25 watt 120 volt light bulb and socket, a line cord and an AC receptacle (you brethren living in countries with 240V mains should obviously use a 240V lamp). Wire the lamp socket in series with the receptacle and the line cord, so that the black (or brown) lead of the cord goes to one terminal of the socket, the other socket terminal is connected to one terminal (say brass) of the receptacle, and the other (silver) terminal of the recept. is connected to the white (blue) lead of the line cord. Forget about the green or green/yellow lead on the line cord if you're using a three wire cord; if you're using a 2 wire cord, follow the above instructions but ignore the colors.
THE FOLLOWING PROCEDURE INVOLVES DANGEROUS, PERHAPS LETHAL, VOLTAGES. IF YOU HAVE ANY DOUBTS OR QUESTIONS REGARDING THE TEST PROCEDURE, DO NOT PERFORM IT YOURSELF. SEEK HELP FROM A PERSON WHO IS EXPERIENCED WITH WORKING AROUND HIGH VOLTAGES. THIS DISCLAIMER IS TO PROTECT SHANNON'S AND MY RESPECTIVE REAR ENDS.
Screw the lamp into the socket, disconnect ALL the secondary wires from the circuit board and make sure none of them can contact one another, plug the amp into the recept. and plug the line cord into the wall. If the lamp lights brightly, you have a shorted turn(s) on one of the windings and are proud owner of an expensive paperweight. If the lamp lights up faintly, or not at all, it's probably OK. You can verify this by CAREFULLY--use clip leads and not your fingers--shorting one winding at a time with power removed, and reconnecting power each time.
The lamp should light at near to full brilliance in each case, indicating that excessive current is flowing in the secondary winding, and, therefore, also in the primary. The lamp acts as a ballast, soaking up the excess current and preventing damage to the transformer (assuming it passed muster in the first place).