The black box is the Q1. you need to test this Main transistor (Q1) with the DIODE tester function of the multimeter as it "works" the transistor. All other diodes need to be checked the same way. On diode test, you look for "open" or zero in one direction, and.3 to.5 volts in the other direction. A good diode or Q1 will show this with the leads one way, then reversed. A burned heat sink insulator is common and should always be checked on code 23. Remove the heat sink and check the insulator for cuts or holes. You should get a Raymond manual