Help with Yamaha A-S series amplifier failure (A-S801)

[Entropy]

Has anybody heard of Yamaha A-S series failing? My A-S801 has a strong left-leaning channel imbalance and is sounding quite thin. Servo protection circuitry kicked in at a relatively low level compared to what the amp should be capable of during demanding dynamic swings. I haven't changed anything with my system since I got the 801, and this issue only cropped up today. As far as I know, I didn't do anything that could've disturbed the amp, I probably haven't touched it at all in a few days.

Other than that, there's a few other details to mention.
-All issues are definitely isolated to the amp.
The headphone section (which runs off of the power amp but through a series of resistors afaik) is perfectly functional. Channel balance and tonality are fine, and I can get far further on the pot with my headphones plugged in than without. Not exactly a demanding load, however.
- I've spilled straight water over and into it on one occasion. This, however, was months ago and after drying the unit out and waiting a few days it was back to working perfectly.
- The amplifier sits in an open environment and is subject to a reasonable- but not extraordinary- amount of dust
- The unit has never been dropped, abused, disassembled, etc, as far as I'm aware. I purchased it secondhand about six months ago from a local audio shop.

 

[restorer-john]

It's quite possible you have damaged output transistors* in the right channel or most likely a damaged speakers A relay. The fact that the headphones sound OK and yet the speaker output is poor is a clue. It could sound fine into a high impedance, non-demanding load like headphones.

To rule out the speaker relay, connect your speakers to speakers B and select them. If the problem goes away- there's your answer. If the problem is still there, we'll need to dig in further with fault finding.

*For it to be OPTs, all four would have to fail the same way and that is incredibly unlikely.

 

[Entropy]

It's quite possible you have damaged output transistors* in the right channel or most likely a damaged speakers A relay. The fact that the headphones sound OK and yet the speaker output is poor is a clue. It could sound fine into a high impedance, non-demanding load like headphones.

To rule out the speaker relay, connect your speakers to speakers B and select them. If the problem goes away- there's your answer. If the problem is still there, we'll need to dig in further with fault finding.

*For it to be OPTs, all four would have to fail the same way and that is incredibly unlikely.

Exact same on B. My headphones- Anandas- have a moderately low impedance of 25 ohms but are also incredibly sensitive, something like 103 dBmW

 

[restorer-john]

My headphones- Anandas- have a moderately low impedance of 25 ohms but are also incredibly sensitive, something like 103 dBmW

The load the amplifier is seeing is 470R+25R, so 495R as compared to loudspeakers around 4R. Huge difference.

If you have a thermal imager, run the amp for 5 minutes and look at the output transistors with the imager. Dead ones will be colder and ones carrying excess current will be hotter than the matching ones. Compare to the working channel.

 

[GXAlan]

I've spilled straight water over and into it on one occasion. This, however, was months ago and after drying the unit out and waiting a few days it was back to working perfectly.

Where did the water spill (front of the unit, back of the unit, etc)? If we looked under the hood, maybe there was something that caused a delayed issue?

Do you live in a high humidity area?

 

[Entropy]

Where did the water spill (front of the unit, back of the unit, etc)? If we looked under the hood, maybe there was something that caused a delayed issue?

Do you live in a high humidity area?

Spilled water on the front right side of the unit, near the pot, tone controls, and power amp section. No idea how it would have taken months to manifest an issue, though. My area is relatively high humidity (73% avg. annual)

The load the amplifier is seeing is 470R+25R, so 495R as compared to loudspeakers around 4R. Huge difference.

If you have a thermal imager, run the amp for 5 minutes and look at the output transistors with the imager. Dead ones will be colder and ones carrying excess current will be hotter than the matching ones. Compare to the working channel.

View attachment 323323

Thanks for the suggestion, but I don't have one handy. Going to reach out to the local dealer that I purchased it from and get an opinion on what might be going on. Possible that I could use a multimeter to test instead?

 

[Deleted member 48726]

That you've spilled water into it might have a-something to do with it.

Corrosion related problems can take a long time to appear and even longer to identify.

 

[Entropy]

That you've spilled water into it might have a-something to do with it.

Corrosion related problems can take a long time to appear and even longer to identify.

@GXAlan @restorer-john Opened up the unit and took some photos if it helps at all. Let me know if there's another angle you'd want. There's a decent amount of dust and fuzz on the components, but I don't think I can see any evidence of water damage. https://drive.google.com/drive/folders/1vP3kaG5IrjsHmQRrmG8oloCuTRBJr4k6?usp=sharing