Another FT-757GXII - Won't turn ON, no lights

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Another FT-757GXII - Won't turn ON, no lights

Postby w6nfu » Sat May 19, 2018 2:55 am

In that there seems to be a lot of interest in the Yaesu FT-757GX, the following may be of help to others. I received this non-working, dead radio last night:

Problems
: Would not turn ON, No Display, no lights except ON-AIR light would illuminate when pressed.
Symptoms: Fan would temporarily spin when the Power button was pressed IN, could hear main relay click.

Voltage Tests: T8 and R8 Voltages on RF Board at PB 1011 were right on (Red wire 7+V on Rx, 0V on Tx, Brn wire 0V Rx, 8V Tx).
Pin 2 of J-4001 on the Display did not show minus(-) 8-volts on Receive. It must show -8V or nothing will work.
Q-4001 Base and Collector both measured 13.2-Volts. This transistor was bad....a common fault in the FT-757GX's.
Cure: Q-4001 (2SC496Y) is very difficult to change so it was done another way. The Display was unscrewed from the front panel with all
the cables still connected. Four side screws were loosened to allow the front panel to slide forward and the Display placed where
it could be worked on easily.
The body of the transistor was crushed with needle-nosed pliers and the remaining pins trimmed to about 1/4" height. A new
BD139 Transistor with its three long leads, was soldered to the three short pins on the pcb. Then the leads and transistor were
folded over 90-degrees on top of other components to allow the top cabinet cover clearance.
Ops Test: With Display still detached but connected, the radio was turned ON and everything works like normal.
Power Output is set to 100-watts in CW Mode, MOX pressed IN. There is a small metal tab sticking down in the center of the front
panel which makes it difficult to re-install the Display. I cut it off with diagonals, then put everything back together.

Dave - w6nfu
w6nfu
 
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Location: Saugus, California, USA

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