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Sony STR-DE345 no display after replacing Q704

Discussion in 'Electronic Repair' started by [email protected], Jun 18, 2005.

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  1. Guest

    Sony 5.1 A/V receiver model:STR-DE345,year:Jan 2000.No power I found
    Q704=MP1620-OPY-M=Sony # 8-749-010-26=2SB1620=PNP=to be shorted base to
    collector (I think) and found F901=3 amp fuse to be open.
    Well I decided to remove Q704 and power up the unit with a 100 watt
    bulb in place of F901 so when I powered up the unit I noticed I noticed
    that the bulb lit bright for about 3 seconds then dimmed down,I did
    this to see if there were any other problems before I ordered Q704.Now
    when the new Q704 finally arrived I put it in and everything works
    great in the stereo except it has no display.
    I measured the voltages at the both front faceplate (display board)
    connectors and they seem to correspond to the voltages stamped on the
    board so my assumption is that IC103=UPD780206GF=100 pin quad SMT
    display driver IC is defective,I hope not.
    Did I burn IC103? if not anyone have any common repair tips for no
    display?.Thanks in advance.

    Dartmouth,Nova Scotia
  2. Andy Cuffe

    Andy Cuffe Guest

    Check the voltage on the display tube. There's should be about 3-5v
    AC across the two end pins and both pins should be around -30v.
    Andy Cuffe

    <-- Use this address until 12/31/2005

    <-- Use this address after 12/31/2005
  3. Usually ( almost ALWAYS on these Sony's) if the one output transistor is
    bad, they both are. It's possible that you also have a bad emitter resistor
    or other small parts bad in the amp circuit.

    That said, if the main fuse(s) for the output side of the power transformer
    are blown, it will seem to turn on normally, but with no display, since
    the -30V line is derived from the power amp power supply. These fuses are
    often hidden under a circuit board attached to the power transformer.

    Mark Z.
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