So, everything is still switching, but...when I was attempting to adjust the bias, which was about 800mA in receive, and about 1.2A with PTT engaged, in USB, 40m drive at 1 mic at 0. When I began to adjust cw from the full ccw position, the
pot didn't do anything until over half a turn, and immediately jumped to 3-5A, and proceeded to pop D7.
?If it's not one thing, it's another!!! Anyway, both D30 and D31 are both OK, dropping about .6v each. Aside from checking Q28 and the 2 finals, what else could be the issue, other than the likely blown pot for the bias?
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-------- Original message --------
From: "Evan Hand via groups.io" <elhandjr@...>
Date: 3/14/25 2:00 PM (GMT-05:00)
Subject: Re: [BITX20] reviving my sbitx v3
Mike,
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As Gordon points out, there is most likely a problem with the receiver TR switch.? As with the transmitter switching, verify the operation of Q28.
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You can also try removing the RF from the circuit with a low drive setting.? Set it up as shown on the voltage measurement sheet.
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If Q28 turns on and off with the PTT signal, then look at the diodes themselves.? You should be able to check the diode in the circuit without power.
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It is good you found this before being forced to replace another set of finals and other components.
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73
Evan
AC9TU
?
--
Mike - K8MCB?
