Re: QMX (rev. 2 + diode) dead again...
|
Jindra, check the continuity of L508. In RX, Q508 should be turned on, but its source and drain should be approximately ground potential. If L508 is open, you will observe 12V at the drain, and perhaps a volt at L508/Q508 source. The inductor may have been mortally wounded in rework surgery.
Your measurements of bias voltage are fine. I do not see anything to worry about there.
JZ
I measured pins 9, 10, 11, 12, 13 of IC402 (band switch):
- pin 9: 2.45 volts (this is the common pin connected to voltage divider R401, R402
- 3.5, 7 and 5.3 MHz, 2.45 volts at pin 13 (Y3)
- 10.1 MHz: 2.41 V at pin 12 (Y2)
- 14 MHz: 2.38 V at pin 11 (Y1)
If I am not wrong, all three voltages should be the same, right? Channel ON resistance of FST3253 should be some 7 ohms and there are no DC connections at pins 10, 11, 12, 13. Does it mean that IC402 is dead (again)?
I also measured voltages at Q508 (2N7002) in RX mode: gate 3.28 V, drain 11.89 V. Does it mean that Q508 is dead, too? I guess, it should be open in RX mode.
j.
Jindra
|
