This Sony STR-DE475 multichannel receiver with MN2488 / MP1620 power transistor pairs shows lower volume level at Left channel. Balance setting is centered. At scope view, signals at equal level before µPC2581V (uPC2581V) preamp ICs, but after them signal level differs. Difficult to take live measures at that point, due to large bridges blocking access to components pins.
As noted in other threads and other forums, these Nec µPC2581V get very hot, cannot stand a finger on them.
https://www.badcaps.net/forum/showthread.php?t=6931
There're about 6 caps that almost touch these preamps: C701, C703, C653, C751, C753 and C603. C601 and C651 are related too but they "live" a bit far away. Measured ESR from these caps and they're dramatically high, some higher than 99Ω, which is the maximum that my meter can measure. All caps in this amp are 85ºC grade, which is clearly not enough for caps close to those "heaters".
Replaced mentioned caps and now audio level is equal at both channels, but we all know that it'll fail again in years, because this is a design flaw. At least now they're 105ºC grade.
Note that C701, C651, C751 and C601 (4.7uF/50V) are coupling caps where L, SL, R and SR pass through, respectively, before entering preamps. It's clear that higher ESR means higher attenuation in this case!
Forgot to say that this receiver had another failure: when knocking front side, speaker relays click. I noticed broken solder joints on connectors (CNS100 - CNP100) that connect two front boards. One pin is for headphone muting switch, that's it.
As noted in other threads and other forums, these Nec µPC2581V get very hot, cannot stand a finger on them.
https://www.badcaps.net/forum/showthread.php?t=6931
There're about 6 caps that almost touch these preamps: C701, C703, C653, C751, C753 and C603. C601 and C651 are related too but they "live" a bit far away. Measured ESR from these caps and they're dramatically high, some higher than 99Ω, which is the maximum that my meter can measure. All caps in this amp are 85ºC grade, which is clearly not enough for caps close to those "heaters".
Replaced mentioned caps and now audio level is equal at both channels, but we all know that it'll fail again in years, because this is a design flaw. At least now they're 105ºC grade.
Note that C701, C651, C751 and C601 (4.7uF/50V) are coupling caps where L, SL, R and SR pass through, respectively, before entering preamps. It's clear that higher ESR means higher attenuation in this case!
Forgot to say that this receiver had another failure: when knocking front side, speaker relays click. I noticed broken solder joints on connectors (CNS100 - CNP100) that connect two front boards. One pin is for headphone muting switch, that's it.
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