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Post by Deleted on Feb 3, 2021 13:46:18 GMT -5
I have acquired a faulty Onkyo TX-NR545 to replace my dead Pioneer VSX-2021, which I was unable to repair due to the faulty DSP chip.
The Onkyo seemed a good bet as it's newer and 'just' showing 'NG SL' on the display. Pressing Enter shows this as 'Detect Protect I'.
I stripped the unit down to remove the main amp board so I had access to the full SL stage circuit as it is clear from the manual that a large proportion is surface mount on the PCB underside. I worked through the circuit and have tested all transistors and diodes with my meter in diode test mode and they all look fine and compare well to the other channels. All power resistors and fuses are intact, so the SL amp stage looks good to me.
I tried clearing the error by pressing the Enter and Power buttons together but it remains the same. I must be missing something but I cannot find any problem with the channel that's being flagged as faulty.
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Post by tjmotter on Feb 4, 2021 19:51:42 GMT -5
These types of issues are often caused by a failure on the pre-amp board. This board sits vertically right in front of the power transistors. The good news is that you know that the Surround Left circuit is bad so you should be able to compare measurements of all the transistors/resistors to any of the other channel (they are all the same). IIRC There are a couple of transistors in that design that typically fail but the failure is usually caused by a blown capacitor (you would see a bunch of debris in the area if this was the case). Resistors on this board also fail pretty often.
In my experience, most of these types of failures occur on components closest to the bottom of the board so I would focus there first.
HTH
Todd
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Post by Deleted on Feb 5, 2021 5:08:08 GMT -5
Thanks for the reply Todd. This design has the pre amp on the same board as the power output stage and uses a lot of surface mount parts on the underside.
I went through the circuit several times and still couldn't find any reason for that channel to flag up a failure.
I tried a couple of times to clear the fault with the front panel buttons and eventually got it to run the amp self diagnostic. That came up as a pass on all channels with the message, check speaker wires.
After a factory reset, the amp now powers up fine, the fault has cleared and it works. I can only assume the previous owner had a shorted speaker lead on that channel, which caused the issue.
Either way it was a bargain and and I now have a working replacement for my faulty Pioneer 🙂
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Post by tjmotter on Feb 5, 2021 9:35:11 GMT -5
Congrats!
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