Re: reviving my sbitx v3
开云体育Evan, I finally got it going! My problem was having more than one problem at a time. Once I replaced everything in the circuit, fixed dry or bridged joints, and put a new set of finals in, it now switches and has output. However, before I even
touch the bias pot, does the other pot have anything to do with this circuit? It doesn't appear to, but I mistakenly put it to full ccw with the bias pot too. What is the pot for and how should I set it?
-------- Original message --------
From: "Evan Hand via groups.io" <elhandjr@...>
Date: 3/10/25 10:10 PM (GMT-05:00)
Subject: Re: [BITX20] reviving my sbitx v3
Michael,
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The first step is to verify that the Q10 Drain goes to zero when TX goes to 3 volts (or higher).? If that happens, Q10 is OK.? If not, it is bad.
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Once Q10 works, verify that the Q9 tab (Drain) goes to 12 volts when the TX signal drives the Q10 drain low.? If that does not happen, remove Q9 and check the operation of Q101.? Do this with Q9 removed to prevent damaging both devices again.
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Q101 drain goes to zero when TX and Q10 are off.? When TX is low, the Q101 gate should go above 5 volts to make Q101 turn on.? When Q10 turns on with the TX signal, Q101 should turn off.? If Q9 is removed, you can verify that the Drain-to-source resistance
is very high with an Ohm meter.? Q101 Drain to Source resistance should be close to zero when TX and Q10 are on.
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An alternative approach is to remove Q101 so there is no short on the 12V line during receive, Verify and replace bad parts, and then install a verified working Q101.? I built a test jig on a small copper-clad board with wires to insert into a component
tester.? I hold the device with tweezers to connect each lead to a separate pad.
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73
Evan
AC9TU
-- Mike - K8MCB? |