Sony STR-DE345 no display after replacing Q704

Jun 18, 2005 2 Replies

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.



Sidney Dartmouth,Nova Scotia Canada



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

snipped-for-privacy@psu.edu

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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