Sony STR-DE845 Surround Receiver
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Most Helpful First | Newest First | + ShareExcellent Beginer's surround sound receiver
No regrets whatsoever
good but with problem
First the center speaker quit and I heard clicking noise from the receiver. Such noise can only come from a relay. So I just switch it to 2-CH mode, since I did not have time to fix it. Then in last week, the receiver finally gave up. It stoped working either right after power-on or after working a several minutes. So I have to take it apart to do something. Here is what I found out. By the way, I am quite an experienced electrical engineer.
The Op-amps in the pre-amp stage were overheated. There are three of these NEC op-amp chips on the main board. They are black big chips mounted vertically. I touched the chips after power-on for 2-3 minutes. They are hot, feels about 55-60 degree C. This is with the cover open, no input signal, no speaker hook-up. Then I noticed some of the leads of the op-amps were de-soldered and the board was black around the chips(open the bottom cover, looking from the back side of the main circuit board). It takes ~160 degree C to soften solder. So the silicon in these chip must be above 180 degree C at that time!
Here is what I think happened. The designer did not give the op-amp chips enough heat sinking. So the chips over-heat. Not hot enough to fail immediately... robust NEC chip design! The solder points got soft when temperature got to ~160 degree C and hardened again when cooled down. After several years of execise, the solder joints became unstable, sometime touch sometimes not. This caused the protection functions to kick in. Then relays started to click on and off, folowed by shut off.
Here is how I fixed it. These op-amp chips have metal slug on back and screw holes for heat sink mounting. SONY did not put in any heat sinks for them. (Come on, it costs <$0.3!) So I resoldered the IC leads. Then I cut three pices of 30mm X 50mm X 0.8mm from a copper sheet, drilled screw holes. Then mounted the copper pieces to the back of the op-amp ICs. Some silicon greese or thermal pad between copper and IC will be very helpful. I used some phase-change material, if you know what it is.
After done that, I hooked up speakers and DVD players and turned it on for about one hour. It was fine. These op-amps are still hot, but should be cooler than before. Someday they may fail just because of running hot for too long. If they fail, I may buy replacement from ebay for $7 each.
Hope you find it helpful. Good luck!
I love my 845, well, not literally!!
The controls were set flat "as always for music" using only the two main speakers, the bass treble and midrange blended really well, the low bass notes common in jungle music were deep and low, and kept good pace with the music, the treble sounded rich and clear. An audiophile "if there really is such a thing" would no doubt think the sound was just brute power with no class, besides you cant get a great sounding receiver for just a few hundred dollars right!!! wrong, you can, and this receiver if you are lucky enough to find one, would be a great place to start.
I found mine in mint condition, I have seen the new 875 and appreciate some of the changes sony have made, banana plugs, front panel hookup, great, but the remote, the front panel nahhhh dont like em! the 845 for looks and that awesome remote wins me over easily, and I intend keeping it for a long long time, just wish I could have found the silver version, WOW I really like those but you dont see that many of them around, hope this helped you.