Re: V4 TX problems and new finals #ubitx-help


 

At 13/12/2019, you wrote:
Two ways to go forward at this time:

1 - Measure the bias voltages on the transistors
2 - Remove the transistors and do typical diode check on each junction

I would do the bias voltage checks.

You are concerned with Q911,Q912, Q92, Q93, Q96 and Q97.

When I measured the voltages relative to ground I got aproximatly 12.3 volts on Q911 and Q912 collectors, 1.13 on the base and .46 on the emitter.

For Q92, Q93, Q96 and Q97 I measured 11.4 volts on the collectors, 1.12 volts on the bases and .46 on the emitters.

See if any of these transistors have the wrong bias voltages. That would indicate which ones to pull to test.

Note, the values are approximate. The important value is the difference between the base and the emitter. Should be around .7 volts. Indicates it is conducting properly and not shorted or open.

Only real test that I know is to measure the RF voltages, That is why I use a 100 MHz oscilloscope.

Try the above and let us know.

73
Evan
AC9TU

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