Evan and others who may be following.
The TP1 and TP2 I mentioned below was a typo, they were TP20 and TP21. I did the same this morning. With volume control fully clockwise. Nice loud hum at Pin 3. Considerably lower hum at TP21, and almost no hum at TP21. Turning the volume control made difference.
This morning I checked the resistance measurements you mentioned at TP20. With radio on it measured 70 ohms RX, 2.36K TX. From what you mentioned then I guess Q74 is faulty? I did not make voltage measurement yet. Where exactly is Q74? I don't see it.
73, Richard AG5M
On Tuesday, November 19, 2024 at 05:09:11 PM PST, Evan Hand via groups.io <elhandjr@...> wrote:
On Tue, Nov 19, 2024, at 01:10 PM, Richard AG5M wrote:
Evan
This morning I fired up the radio again. Very low volume, but after half a minute, the volume came blasting back. That lasted for some 10 seconds, then went low again. Stayed low.
I have touched TP1, TP2, and Pin 3 of the LM386. I hear a faint hum at TP1, slightly louder at TP2, and a very nice loud hum at Pin 3. So, it's not in the audio chain - would that be right? If right, where to look next? Time to bring out the freq counter and Oscope?
73, Richard AG5M
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Was that TP1 and TP2, or TP21 and TP20?? All are on the board.? TP1 tests the antenna input, TP20 tests the audio after the demodulator, and TP21 is the input to the audio amp with muting.
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With the volume control fully clockwise, the AC hum should be the same when touching pin 3 of the LM386 as TP21.? If not, then there may be an issue with the volume control.? Try turning it back and forth to see if there is a broken connection.
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Another test is to verify that the mute MOSFET (Q74) is switching correctly.? Measure the gate voltage of Q74.? It should be zero when receiving and 5 volts when transmitting.? Also, you can measure the resistance from TP20 to ground with the radio on.? It should be higher than 5kOhms while receiving and less than 200 Ohms when transmitting.? If not, then Q74 may be bad.
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Another problem I have seen with low signal strength is related to the Raduino board.? The Si5351 chip failed to lock at the right frequency, which would appear as a jittery signal on any of the three clocks to the mixers and demodulator.? In particular, the BFO seems to drop in and out of sync.? This could be the case for any of the three clock signals.? To test the Raduino, I removed it from the radio, powered it from a USB connection to my PC, and measured the outputs on the mainboard connection.
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73
Evan
AC9TU
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Richard AG5M