Hi-Fi Stereo went BOOM

[JOHNNY LARGE]

Originally Posted by Mooly

This isn't easy at the end of a keyboard.
I would try comparing one channel against the other, and it may be worth seeing if the other channel actually works OK. That means taking the output from pin 15 to a speaker, not directly, maybe through a 100 ohm to begin with, or a cap to protect it if anything happens. Assuming thats OK it should be possible to compare then.

So i came across this thread as i had the same problem with my garage stereo. It turns on, but the relay won't kick over. I followed the thread through, and have a few questions.

First of all, my amp is a different model, but very similar it is a st4221II
here is the diagram


here are my readings at the pins when energized
1= 46
2=47
3=0
4=7
5=0
6=-50
7=50
8=3
9=-53
10=-53
11=-54
12=54
13=54
14=46
15=2
16=-54
17=44
18=0
19=2
20=0
21=47
22=47

SO i tried what was quoted above, wiring the speaker directly to pin 15, and the speaker worked but it was very quiet, and it could not be adjusted. what does this tell me? Does that mean my amp is cooked? both not producing enough power, and shorting out somewhere causing the protection to block power to the relay?

Or is there something after the amp that controls volume, and is the fault somewhere in between either pin 15 or 12 and the relay?

any help/advise would be appreciated.

[Mooly]

Pin 12 voltage is incorrect. DO NOT attempt to connect a speaker to this. Looks like the STK is faulty as a first guess.
The IC contains two identical channels, outputs on 12 and 15.

[JOHNNY LARGE]

good point, i just tried it on 15, as the voltage was low. if i disconnect the other channel (pin 12) my relay should in theory kick on, if all other components are in working order.

I have 53 volts across the relay, and both contacts are open. one contact is holding 2 vdc, and the other 53. so prtoection is telling it to hold both contacts open?

[JOHNNY LARGE]

so I interrupted voltage coming from pin 12, and the relay kicks over. but the sound coming from the speakers is still nothing more than a whisper. is the voltage in pin 12 suggesting that the amp is shorted on one channel, and the voltage in pin 15 suggesting that the second channel is just to weak to produce and sound?