On bally boards the transistors will need to be tested 2 ways.

For the larger square transistors:

1: On the diode test.
Put the black lead of your meter on the outside "cathode" leg (labeled "C")
Put the red lead of your meter on the outside "gate" leg (labeled "G") Your meter should read .4 to .6 volts.
Swap the meter leads. Now the meter should read 1.4 to 1.6 volts.

2: On the continuity test. Test the other sets of legs and make sure they are not shorted.

On the smaller transistors:

1: On the diode test.
Put the black lead of your meter on the "cathode" leg (labeled "C")
Put the red lead of your meter on the center "gate" leg (labeled "G") Your meter should read .4 to .6 volts.
Swap the meter leads. Now the meter should read 1.4 to 1.6 volts.

2: On the continuity test. Test the other sets of legs and make sure they are not shorted.