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Discussion Starter · #1 ·
Bought this brand new from Circuit City a long time ago. It was my main home theater receiver for a few years. It started acting up so I tucked it away and replaced it. I have now pulled it back out and found that IC501 was the problem for the random false mute (didn't actually make the mute LED turn on, but the chip muted it self) on power up. I replaced it, and put heat sinks on all the preamp UPC2581's.
Now the audio is back and it works again.

But, the set up now is just two large front speakers, no sub or surround speakers. Now I can notice the left channel is weaker then the right. I've already swapped the speakers to rule out them as being the problem.
The left channel still sounds OK, no weird audio anomalies, just the bass is weaker then the right channel.
It could have been this way for a long time, just never noticed because a sub was used and the front speaker were smaller and crossed over.

I've done some googling and found I'm not the first person to have a weak channel on a STR receiver in the left channel. It seems to always be the left, and not the right. So there must be a common design problem and common part failing.

I don't have a schematic or service manual, so I'm hoping some one here has some knowledge one these receivers and knows the common problems. I'm guessing a failing cap or over heated resister between the pre-amp and main output transistors. I don't think it's a bad output transistor because the sound quality is still good.

Thanks for any help! I really want this working again!
 

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Discussion Starter · #2 ·
I was doing some more searching and found:

"Check the soldering on the upc2581v ICs near the outputs. They tend
to run blistering hot and desolder themselves over time. For best
results you may have to remove them, clean the pins and resolder. Any
electrolytic capacitors near them may have failed due to the heat.
I've also seen the ICs fail from heat. I don't like Sony receivers
because parts like these ICs run too hot. I've installed heat sinks
on the upc2581vs in my own receiver."
-Andy Cuffe
There are some electrolytic capacitors right next to the back of the IC501. And that chip does get really hot. So if the audio signal passes through any of those caps, and the cap is cooked, I could see that being a problem.

What do you think? anyone?
 

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Discussion Starter · #3 ·
Found it.
All the electrolytic capacitors directly next to the upc2581v heat sink were cooked. The capacitance was so low they would'nt even register on my meter.
There are a pair of 50v 22uf and one 10v 220uf cap next to the chip heat sink. Replacing the 22uf did'nt make any chances. But replacing the 220uf fixed the weak left channel. The other 220uf (for the right channel) is kiddy corner and away from the heat sink, so it did'nt get cooked.
Would be wise to replace all the cap's, both the 22 and the 220's, for all the channels.
 

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Found it.
All the electrolytic capacitors directly next to the upc2581v heat sink were cooked. The capacitance was so low they would'nt even register on my meter.
There are a pair of 50v 22uf and one 10v 220uf cap next to the chip heat sink. Replacing the 22uf did'nt make any chances. But replacing the 220uf fixed the weak left channel. The other 220uf (for the right channel) is kiddy corner and away from the heat sink, so it did'nt get cooked.
Would be wise to replace all the cap's, both the 22 and the 220's, for all the channels.
Thanks for the info If i ever pick one of these up I will have an idea of what could be the issue.
 

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Discussion Starter · #5 ·
Thanks for the info If i ever pick one of these up I will have an idea of what could be the issue.
Thanks. Seems to be a real common problem with a lot of Sony STR Receiver.
That and a bad cap in the power supply for the low voltage electronics, it will force a shut down "no power" symptom.
 
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