dfarrington
Member
Hello, I am new to working on the SX-780 and just getting back into electronics after 30 years. My SX-780 at first had a bad STK so I replaced both. Everything was fine and I hooked it up, turned it up nearly half way with 4 speakers and the protection circuit kicked out. I opened it back up and found the right channel STK shorted. I removed the right channel STK and protection okay and left channel worked. Before I stuck another STK in, I pulled the .22ohm resisters on the right channel and replaced with new. When I went to test to see if I still had the left channel, the relay did not click. I am now lost. I have pulled both STK's and here are the voltage reading across q25, 19 and 20 (3 transistors with heat sinks)
Q25
13.6
14.1
27.3
Q19
39.9
40.4
51.4
Q20
1v
0v
-54.3v
Left Darlington pins with no STK in place
1 1v
2 -41.5v
3 0v
4 0v
5 0v
6 0v
7 41.5v
8 0v
9 41.5v
0 39.5v
Right Darlington pins with no STK in place
1 1v
2 -41.7v
3 0v
4 0v
5 0v
6 0v
7 40.8v
8 0v
9 40.8v
0 39.6v
Q25
13.6
14.1
27.3
Q19
39.9
40.4
51.4
Q20
1v
0v
-54.3v
Left Darlington pins with no STK in place
1 1v
2 -41.5v
3 0v
4 0v
5 0v
6 0v
7 41.5v
8 0v
9 41.5v
0 39.5v
Right Darlington pins with no STK in place
1 1v
2 -41.7v
3 0v
4 0v
5 0v
6 0v
7 40.8v
8 0v
9 40.8v
0 39.6v