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Post by niftyyetthrifty on Aug 5, 2023 16:04:01 GMT -5
So bought this secondhand, seller noted that the volume control randomly wouldn't work as it should but it worked most of the time. I figured possibly a dirty potentiometer and I paid a relatively small sum so was worth a go. When it arrived, gave it a cleanup, cleaned the pot and tested, all worked. Got it all plugged in and all worked, so far so good. However next day went to turn it on and the power led went from solid red to flashing red, tried the onkyo suggested remedy of turning it off for an hour and resetting it but no luck Pressing the power button i can hear the transformer hum and then a relay click.
Any advice on locating the culprit? Seller refunded me the cost of the amp so if I can fix it, then its a bonus. Thanks in advance
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Post by serafis on Aug 11, 2023 17:09:39 GMT -5
Flashing standby LED usually indicates protection mode. When power is applied, a standby power circuit powers up the main processor, which does some initial checks, turns on the main relay (the click you heard) to power the amplifier stage, and looks for any abnormal voltage/current flow such as DC offset on the speaker outputs before activating the speaker relays. If it finds any issues, it immediately shuts power down to avoid any further damage and flashes the LED to indicate that there is a fault.
A common cause of protection mode is a failed output stage (blown output transistors) on one or more channels, most often caused by a speaker short.
You can check the output transistors (the big ones attached to the heatsink) with a multimeter - there are two for each channel. If any of them show a short between their legs, or measure differently from the others, then there's the likely culprit. Or another way is to check the big white 5W ceramic resistors near the power transistors - if any of them show open circuit between the center pin and either of the outside pins, that's a problem channel.
Power transistor failures will often (usually) cause other components to fail, such as fusible resistors, transistors and (sometimes) capacitors on the amplifier board and also on the preamp driver board (the vertical board that plugs into the main board). You'd need to download the service manual and measure each component on the driver and amp board for the failed channel and compare with a good channel, replacing any that look bad or don't measure up.
Also check the preamp driver board for dry or cracked solder joints especially around the legs of the larger transistors (wiggle them gently while inspecting the underside of the board), as I've found that on Onkyos the heat these generate over time can cause the PCB tracks to lift or break - these can usually be repaired by scraping the enamel off the PCB track where it's still good, and soldering a piece of stiff copper wire from there back to the failed joint. Messy, but it works!
Hope that's helpful and good luck!
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