Sony Receiver shows TV/DBS Protect

Discussion in 'AV Receivers' started by Chris Dawley, Aug 16, 2004.

  1. Chris Dawley

    Chris Dawley Auditioning

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    Hi,

    I am working on a Sony STR-DE515 Receiver. When I turn it on, it comes up as TV/DBS Protect. How do I fix it? While I was poking around on the inside of the receiver to find out what would be causing it, I turned the receiver over and noticed about 5 burnt components, but I am able to get ohm readings off of he components. Any ideas on how I can fix the TV/DBS Protect problem?

    Thanks,

    Chris
     
  2. Steve Berger

    Steve Berger Supporting Actor

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    You probably have shorted output transistors. First , after you take the bottom panel off , get a 1000 ohm 2 watt resistor and discharge the large power supply filters before you measure anything else. You would need to check the output transistors for shorts and the emitter resistor for an open connection. (the three legged ceramic resistor , usually .22 ohm) If the outputs are not shorted then you would need to check bias on the outputs (+1.0 vdc and -1.0 vdc on the base leads) If bias is off then the driver IC and/or feed resistors are bad. Don't forget to check for open fuses but don't replace any before checking for shorted outputs.

    If you crossed a speaker lead the outputs will short out instantly. High temperation operation will sometimes cause the driver ICs to fail.

    If all of this is Greek to you or you're not comfortable changing components or circuit tracing then you're not likely to solve the problem. I service these units and there are no nuisance problems that will put them into protect. Sorry to be so pessimistic but be very carefull of the filters , they carry enough of a charge to weld a screwdriver.
     
  3. Chris Dawley

    Chris Dawley Auditioning

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    Where are the power supply filters located? I am assuming near the power supply. This receiver used to be my aunt's. I am guessing that they must have crossed a wire or shorted something out during hooking the receiver up to short it out. The only panel that I see that will come off is the one with the lightning bolt on it. There, I see a voltage regulator that I measured voltage across and found it around 15V. The part number is 78M15. That is also the area that I found the burnt components. What color are the power supply filters? I see 2 large caps that are both 71V 10000 micro-farads. To the left of those if looking from the receiver display facing you, is a big square block that is black and has a white label that reads BD21A11G. Behind that is an upside down circuit board. Under that is where the power comes in at. I do see a black transformer looking component in the same area as the power plug. It has a part number of M7C-2M. Hope this information helps.

    Thanks for your help.

    Chris
     
  4. Chris Dawley

    Chris Dawley Auditioning

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    I found out what my problem was. I was looking on the web for a schematic and ran across another post about someone having the same problem. It turns out that their problem was related to 3 pairs of transistors underneath the bottom cover, labeled MN2488 & MP1620. I found the 2 bad ones by measuring the voltage across them and the pair with the voltage not matching what the other pairs had across them were bad. I de-soldered the transistors and the unit started functioning like normal. No more flashing protect. Hope this helps.

    Thanks,

    Chris
     

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