Need some help / advise please ...

[Juicer]

ANY HELP or GUIDANCE would be greatly appreciated - - My Onkyo 4500 MK II made a popping noise and I saw smoke. I took it apart and found the left channel was damaged - R518 smoked and R520 cracked open ( see attached file ) - I found that Q506 and Q506 are shorted E to C and R522 OPEN - I ordered the parts from Mouser and replaced them and powered it up - NO SMOKE

I checked the voltage at the speaker outputs ( ? DC Offset ?) and the right side is 2.5mv and the left side 6mv. The manual states to check and adjust the Idiling Current at test points ID and CT ( please the attached file ) and adjust at R517 to 40mv +- 10mv. I have 0mv on the left and is unadjustable - I checked the right side and have 45mv that can be adjusted.

The manual also states to check the Center Voltage and make sure it is +-50mv. The right side has 40mv and the left side is flucuating at 0 - 10mv. There is no mention of how to adjust this??

??? Any sugestions??? I hooked up speakers and they sound good.

 

[Binkman]

I checked the voltage at the speaker outputs ( ? DC Offset ?) and the right side is 2.5mv and the left side 6mv.

Yes that is dc offset. Very good. The center V is in spec. Not sure about idle the test points for one channel and the other... getting zero reading. I see two VR's in the schema.

 

[century tek]

Usually when a power transistor shorts, it takes out other things with it down the line as you have discovered but it can also take out the emitter resistors. Have you checked them?

 

[Binkman]

I hooked up speakers and they sound good.

@century tek I think he got parts covered just can't get a reading on his meter for the one channel. He prob. figured it out anyway.

 

[century tek]

That's why you need to check the emitter resistors.

 

[shelly_d]

Check the voltage across R522 and R523. They should be the same and should be a close match for the same voltages on the other channel. If they are, then the issue is probably somewhere between R522 and the test point ID. Check to see if that one resistor, R525 is open. If it is, that is your problem. If not, look for a open on the circuit board. With the unit unplugged, use an ohm meter to test continuity between Id and R525, then between R525 and R522. There may be an open trace on the board due to the failure or parts replacement.

Good Luck