On 03/02/2018 22:11, Kent Berglund PhD wrote:
Hi Alan,
I get 0v at the other end of R42, which is the drain of Q4, with 5v on the gate with Key Down Tx mode.? I have checked connections in this area and all seem to be good.? ? Please note the DC voltages that I have measured. (Keydown current is 111ma (w/o the LCD display)? Rx current is 88mA.? Voltage at 12.3vDC.
Kent,
Your picture makes it clear!
Either R42 is open circuit, test with ohmmeter.
Or Q6 is open circuit. Unusual, they usually fail short circuit but either way is possible.
I'm thinking this is what you will find, Q6 is open circuit.
You must be careful, it is possible that one, or more of the output BS170s Q1, 2, 3 has shorted and caused Q6 to fail. This has happened before but in all other cases Q6 failed short-circuit.
Measure the resistance from the drains to ground, it should be high, maybe 10K or more.
A low reading will certainly indicate a shorted BS170 but I'm not sure if a high reading will definitely mean the BS170s are good.
If a high reading is obtained I'd still recommend changing the BS170s for safety. But in fact I would probably first test carefully. After replacing Q6 and attaching power meter and dummy load a very quick key should produce 12V on Q6 collector and power out shown on the meter. Current taken by the CQX should be the normal around 500mA.
Failed BS170s are usually caused by inadvertently transmitting with no dummy load or matched antenna connected.
73 Alan G4ZFQ
