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Realistic STA 820, assistance

Reyhifi

Reyhifi

Well-Known Member
Guys I finally got some parts to get going on the 820. Had no sound, you could clearly see, some cooked resistors and awful looking transistor. So I replaced the bad components. Power it up on the DBt, and the resistor went again. So I got a couple of filter caps, put them in and up in smokes goes the resistor. I disconnected both caps checked the rectifier. Correct 56V ac and 39,DC on both channels. So my limited skills are showing, not sure we're to go now. The left channel is the one causing all the grief.
I'm adding a photo. The schematic is pretty bad and is available at hifi. If I post a photo it would be worthless.
So any ideas
 

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Reyhifi said:
Guys I finally got some parts to get going on the 820. Had no sound, you could clearly see, some cooked resistors and awful looking transistor. So I replaced the bad components. Power it up on the DBt, and the resistor went again. So I got a couple of filter caps, put them in and up in smokes goes the resistor. I disconnected both caps checked the rectifier. Correct 56V ac and 39,DC on both channels. So my limited skills are showing, not sure we're to go now. The left channel is the one causing all the grief.
I'm adding a photo. The schematic is pretty bad and is available at hifi. If I post a photo it would be worthless.
So any ideas
Click to expand...

You have a short somewhere. Have you pulled the output transistors to check their condition? It looks like the burnt components are right before the outputs.

1692897923220.png
 
Reyhifi said:
Hi thanks for the reply, a pain to remove. But I did it, shorted all but 1. So that's next, maybe I'll finally get it done.
Click to expand...

Before installing the new outputs, I suggest replacing the obviously burnt components and testing others in the vicinity to make sure they're still good. Then power up the unit on a DBT (probably a 60 or 75W bulb). If all looks good, then install the new outputs (with insulators and thermal paste) and try again. Good luck.
 
One more thing. It's interesting that the outputs blew on your receiver since it seems to have a protection circuit. You might want to check that area too, but I'm not sure where that would be on the schematic. There doesn't seem to be a relay switch or separate protection board.

1692985328584.png
 
Last edited:
Gnesen said:
One more thing. It's interesting that the outputs blew on your receiver since it seems to have a protection circuit. You might want to check that area too, but I'm not sure where that would be on the schematic. There doesn't seem to be a relay switch or separate protection board.

View attachment 2968277
Click to expand...
Actually is not my unit, belongs to a friend and as I understanded somehow someone pulled on a speaker and dead it went.
 
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