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Recieve audio

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When built and tested on air, V4 uBITx,? I had good audio from the speaker and good audio on transmit.. I could never get the supplied socket to work for me. I just pushed the speaker mono plug partially in. No problems. Or was this the start of the problem?. I then? built a new aluminium? box and fitted a 3.5 Nextion screen. All was working well. Then I got creative, I played around with the supplied socket to get it to work as described, it was wired exactly as shown in the instructions picture, to no avail. I then noticed I had lost 75% recieve audio.? ?I fitted a mono socket instead of the supplied socket, to no avail, I can hear close stations, but they are very quiet. On Nextion screen attn is on zero, not that. I have spiked or over loaded something pushing the speaker plug in and out of the socket, but what??
I can transmit 10 watts on 20M with good audio so don't believe transmit is a problem. Has any one, any ideas just what I have spiked, or missed, and how to rectify the fault, Please
John Graham ZL4RO
 

John,

Firstly I am thinking socket or plug wiring problem. Check by directly connecting a speaker to the two speaker leads from the board.
Next maybe some component failure in audio amp.

Connect an external amplified speaker to the top and bottom connections on the volume control and see is that is OK.

If that is fine then you have start checking audio amp voltages.

Raj

At 22-01-19, you wrote:
When built and tested on air, V4 uBITx, I had good audio from the speaker and good audio on transmit.. I could never get the supplied socket to work for me. I just pushed the speaker mono plug partially in. No problems. Or was this the start of the problem?. I then built a new aluminium box and fitted a 3.5 Nextion screen. All was working well. Then I got creative, I played around with the supplied socket to get it to work as described, it was wired exactly as shown in the instructions picture, to no avail. I then noticed I had lost 75% recieve audio. I fitted a mono socket instead of the supplied socket, to no avail, I can hear close stations, but they are very quiet. On Nextion screen attn is on zero, not that. I have spiked or over loaded something pushing the speaker plug in and out of the socket, but what?
I can transmit 10 watts on 20M with good audio so don't believe transmit is a problem. Has any one, any ideas just what I have spiked, or missed, and how to rectify the fault, Please
John Graham ZL4RO
 

John

rarely can we blame a mechanical connection for diminished audio - and you can certainly press on the connection to confirm.? is the CW sidetone still loud?? that would confirm part of the audio path - meaning then any issue would be in front of where it is injected.? we could possibly blame a degraded solder connection somewhere.?

most of us find speaker audio in the V4 to be a bit light, but headphone audio is vigorous in most modern headphones (at least the ones I have).? as for boosting audio - I am using an external audio filter for CW/SSB filtering - and it ends with a LM386 to further boost audio.?

well sometimes in inject signals to trace low receive audio - but usually before this I take my finger along the path just connected to the antenna - and often I find the issue when I touch it.?

never a bad idea to check external RF cables - that was cause of my last similar issue.?

Curt
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Hi Team, First I tested CW it works ok,? but side tone, has the very low audio output, same as the speaker. I attached a speaker to the wires from the output of the board, no improvement, No improvement at the volume control either.
I then fitted a audio pre amp, this certainly lifted the audio, but it was harsh to listen to.??
Then checked Q 70, 71, 72 73, I put my finger on top of each as instructed to see what would happen. Q71 and Q73 when touched produced a low hum. (pre amp still connected). Q70 and Q72 no hum. What do they do?, Could these two be faulty? (Q6 produced a hum and had voltage on all 3 legs? the others only had voltage on some legs or none at all). Are these the audio amp SMD transistors. How do I test them please.
 

If you touch the Q6 collector you will get hum BUT there should be NO voltage on any pin. The voltages to
Q6 is only while transmit. So investigate this.

If Q6 has DC voltage then you should hear your voice from mic through the amp!

Do the D15/D16 quiescent current mod that I have repeated posted before. It will improve the low level audio and
remove distortion if you have. The rig will sound louder and clear instead of crackly!

Raj

At 23-01-19, you wrote:
Hi Team, First I tested CW it works ok, but side tone, has the very low audio output, same as the speaker. I attached a speaker to the wires from the output of the board, no improvement, No improvement at the volume control either.
I then fitted a audio pre amp, this certainly lifted the audio, but it was harsh to listen to.
Then checked Q 70, 71, 72 73, I put my finger on top of each as instructed to see what would happen. Q71 and Q73 when touched produced a low hum. (pre amp still connected). Q70 and Q72 no hum. What do they do?, Could these two be faulty? (Q6 produced a hum and had voltage on all 3 legs? the others only had voltage on some legs or none at all). Are these the audio amp SMD transistors. How do I test them please.
 

In addition please check the resistance with a multimeter from TP21 to ground, it should be 11k from my circuit reading.

If it is low then some issue with Q74 mute FET. We'll go into that if you confirm.

Raj

At 23-01-19, you wrote:
If you touch the Q6 collector you will get hum BUT there should be NO voltage on any pin. The voltages to
Q6 is only while transmit. So investigate this.

If Q6 has DC voltage then you should hear your voice from mic through the amp!

Do the D15/D16 quiescent current mod that I have repeated posted before. It will improve the low level audio and
remove distortion if you have. The rig will sound louder and clear instead of crackly!

Raj

At 23-01-19, you wrote:
Hi Team, First I tested CW it works ok, but side tone, has the very low audio output, same as the speaker. I attached a speaker to the wires from the output of the board, no improvement, No improvement at the volume control either.
I then fitted a audio pre amp, this certainly lifted the audio, but it was harsh to listen to.
Then checked Q 70, 71, 72 73, I put my finger on top of each as instructed to see what would happen. Q71 and Q73 when touched produced a low hum. (pre amp still connected). Q70 and Q72 no hum. What do they do?, Could these two be faulty? (Q6 produced a hum and had voltage on all 3 legs? the others only had voltage on some legs or none at all). Are these the audio amp SMD transistors. How do I test them please.
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Hi Raj.. Found? T21 - 10.66 ohms by my? multi meter.? While probing around with multimeter I found the problem. I had a senior moment and put the positive and negative wires on the wrong way around to the mono speaker socket. It happens to us oldies on occasion.
Amazing how the uBITx put up with the wiring the wrong way around, without something else failing. I now have noise coming out? of the speaker.
I will search the forum to find the D15 D16? modification
It's thanks people like your self, and others on the uBITx net, that are there to point the likes of me and others in the right direction, when it comes to diagnoising. Thank you very much for taking the time to assist and reply to my questions.
Happy uBITx operator
John Graham ZL4RO


?,
 

Thanks John,

Good find!

However I am surprised at your reading at TP21 which should be TX like reading.

RX = 12K without power, 5-7K with power depending on probe polarity.
TX = 18 Ohms.

Raj

At 26-01-19, you wrote:
Hi Raj.. Found T21 - 10.66 ohms by my multi meter. While probing around with multimeter I found the problem. I had a senior moment and put the positive and negative wires on the wrong way around to the mono speaker socket. It happens to us oldies on occasion.
Amazing how the uBITx put up with the wiring the wrong way around, without something else failing. I now have noise coming out of the speaker.
I will search the forum to find the D15 D16 modification
It's thanks people like your self, and others on the uBITx net, that are there to point the likes of me and others in the right direction, when it comes to diagnoising. Thank you very much for taking the time to assist and reply to my questions.
Happy uBITx operator
John Graham ZL4RO

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