I figured I would post this for anyone out there having the same problems as I did for this HT receiver...
The Sony STR-DE597 started to act up when going from A speakers to B speakers or even going to or from headphones. The left channel would usually cut out until I turned the volume up loud enough then it would POP back into action. This got worse and worse until I had no audio in the front L and R channels when I turned the unit on. The volume up trick stopped working. This receiver has pre driver IC's feeding output transistors and I feared that the IC's were cooked or something expensive to fix like that.
To take the main board out, take the top off (straight up, don't break the tabs) then the back panel needs to come off. From there disconnect the cables to the power supply and front panel, unscrew the board and heat sink and take the whole deal out. Fun right? I wanna beat these engineers up too.
I opened her up and took out the main board (the one the heat sink is attached to). The bottom of the board was discolored like it was getting too hot in two main places. The worst place was where the predriver ICs were. There are two ICs that are dual channel for the front LR and surround channels and then there are two separate ones for the center and surround back channels. These ICs get WAY too hot even at idle, they don't have heat sinks on them and there are electro capacitors really close to them. No excuse for that at all SONY, that's just piss poor engineering.
The soldering job on it was complete dog crap -it looks terrible. A lot of the smaller joints were not filled in enough and it all looked like unleaded cheap solder. I figured the solder was cracking due to heat so I went through it and removed the old and started over. I suggest to anyone doing this to use some kind of desoldering iron to limit heat to your chips. You can get one for under 20 bucks at Radioshack. Don't work one chip too long and flux is going to be your friend for both desoldering and for the new stuff. Make sure that you don't let the new solder drip down the leads of the output trannys and short the lead to the heat sink cause they don't bend the transistor leads at all.
Anyway, I did new solder on the output trannys, the pre driver ICs and to a lot of the other cold looking joints on the main board. There are a few transistors that also get hot on that board which are worth redoing. Didn't fix my problem though, UUHG! Turns out it is the relays. The contacts went bad. These relays are not fully sealed and to open them, you have to get something in the seam at the bottom of them and pop the covers off of them. There are 4 relays you have to clean and each one has two contacts. One main one close to the HP jack, then three close to the speaker terminals that are for front LR-A, front LR-B and I forget what the other one is... center and surround back I think. Not that easy to take off the covers sometimes so check the solder didn't crack after fighting with them.
I tried just using a piece of grocery bag paper with alcohol on it to clean them but it didn't work at all. I had to get some 220 grit sand paper and stick it in the middle of the contacts, then manually close them (push down on the top of the metal part) and move it back and forth. I went up and down on one side of the contact and side to side on the other. Then I blew out the dust with compressed air and hit it with some contact cleaner/lube. I tested them by sticking an adapter in the head phone jack a bunch of times to open and close them while hooking a test speaker up to each channel to make sure that they were working well.
This fixed my problem. I then got a grinder and cut a circle out of the top of the chassis lid and attached a 120mm computer fan to it right over where those ICs are. I aimed it straight down at them. I tapped into the switched main 120v line feeding the transformer in the receiver then ran a cord out that plugs into a little wall wart that feeds the fan. So far so good.
I don't abuse any of my audio stuff and even though this isn't the highest end receiver I don't think there is any reason that it should fail this soon or run so hot so I think I'll be avoiding SONY receivers in the future. Hope this helps someone out there. If it doesn't work, don't forget to test each transistor while you have the solder removed to eliminate them failing from the equation. Also test if you have DC coming out of the speaker outs before connecting any speaker you care about to them. DC should not be present. If it ends up being a problem with the predriver ICs then throw the thing away and get another receiver with discrete transistors because the part cost will probably not be worth the fix. You can also check your positive and negative power rails for your main output stage and the op amps but it won't be all that easy cause there is no removable bottom of the chassis.
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