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Sony STR-DE345 no display after replacing Q704

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
 
A

Andy Cuffe

Jan 1, 1970
0
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

[email protected]edu <-- Use this address until 12/31/2005

[email protected] <-- Use this address after 12/31/2005
 
M

Mark D. Zacharias

Jan 1, 1970
0
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

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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