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Sony STR-DB940 pulled back from the brink

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    #61
    Re: Sony STR-DB940 pulled back from the brink

    Thanks for the photo Furball...I have had my STR-DB940 since 2004 and it just started clicking last year...I have been searching for info and more importantly pictures of the areas to touch up the soldering...will give it a shot.
    Much appreciated...
    Rob

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      #62
      Re: Sony STR-DB940 pulled back from the brink

      I have bought a second hand Sony STR-DB940 that was advertised as being in working status but it turns out it can work only in stereo mode / 2ch direct mode.

      When I try to send a test tone it tries to burn down the speakers! Same happens when I just set it on 5.1 input mode , dobly prologic, custom sony soundstage etc.
      There is a terribly loud sound coming from center and rear speakers and the volume of this sound is totally independent from the setting of the volume control.

      So there is something definitely wrong there:

      I opened both the cover of the amp and the service door on the underside and upon closer inspection noticed some possibly cold solder joints on the AMP pcb. But the digital board had serious discoloration due to heat and some roasted capacitors around the area of 5V regulator and 3.3V regulator.

      I took out the caps and they are indeed bad.

      While it was on mains and powered on I couldn't keep but notice that this area was getting very hot.

      I know that there is already reference about those 2 issues.

      But what I discovered and couldn't find reference in any online forum is that there is also an aera on the AMP pcb that gets so hot that the regulators can get cold solder joints and this can cause issues too.

      This area is not accessible, without totally removing the AMP pcb outside the amp and this required practically removing , FM tuner, digital board, svideo board, rca video board and the output speaker board.

      Then, one can carefully remove the amp board and have access to the area of the regulators and especially the -5V that is mounted without a heatsing because Sony engineers did a terrible job designing this thing.

      But wait, there is more!

      IC501 and IC701 also have cold solder joints on my unit and the board has signs of overheating.

      Finally, I decided to desolder the 3 remaining boards: the board of the 2 huge primary capacitors 15000uF 71V, DC1 and the AC board and DC2 board. Surprisingly I found cold solder joints on DC2 as well and pcb discoloration.

      What a terrible job Sony!

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        #63
        Re: Sony STR-DB940 pulled back from the brink

        Some pics
        Attached Files

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          #64
          Re: Sony STR-DB940 pulled back from the brink

          I know this is an old post but maybe you guys cam help me. I have a Sony STR-K840 (110 volts-US version) and it started to enter protect mode. I opened up the case and got rid of the dust with compressed air, tighten all the screws and powered up the device. Nothing changed, still in protect after first relay and before second relay. So I disassembled the board and reflow all the solders on power mosfets, IC501 (STK350-230) and IC 701 and 702 pins in case of any cold solders. In the second try the relays started to chatter continuously. After a couple of attempts, glass fuse blew up on the power board. Then I desolder all of the power mosfets (MN2488 and MP1620) from the pcb and tested with multimeter. one pair of the mosfets shorted. I know those need to be replaced. What I wonder is situation of IC 701 and IC 702. Just before fuse blow, I sensed a heat from upc2581V (IC701 and 702) with my finger. I know those components get really hot when they run. But I wonder whether I fried upc2581v? Because, from what I see, it is really hard to find replacements for that IC.

          Is there a way to test that IC with multimeter? Any ideas? Thanks in advance

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