By the way if the volume control is set to the minimum end you will not get anything.? Also if you inject your 0db signal it will be shorted out at minimum setting.
Try setting about half way when you touch the centre pin with either wire or signal.? If you still get nothing but you do with putting on pin 3 of LM386 then the connection between is broken. either internally in the wire insulation,? a? dry joint where the volume control socket fits onto board or dodgy connector.
Also it is not a good idea starting at the A/e connection and working through system.? Start at the output end and work towards the A/e.
Cheers,
Will.
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On 02/10/17 12:09, Vince Vielhaber wrote:
Unplug the vol control from the board and see if touching the pin that would connect to the wiper gives you noise.? That isolates the preamp from the circuit.? If you get the noise you used to get, look at the preamp stage.? If not, look at the LM386.
Do you have a scope?
Vince.
On 10/01/2017 06:02 PM, Ken Macy wrote:
On Sun, Oct 1, 2017 at 12:00 pm, Ashhar Farhan wrote:
??? audio preamp might be busted. the LM386 seems to be working (from
??? the test that you performed). check the voltages around the audio
??? preamp's base and collector.
??? if the LM386 gives you noise, does the volume control give you noise
??? too? trace the connectivity from pin 3 of the LM386 to the volume
??? control's middle lug. if the noise ensues when you touch a wire to
??? the middle lug of the volume control, then move to the upper lug
??? (not the one connected to the ground), if that works, then, check at
??? the collector of the audio preamp. essentially, you hve to get to
??? the point beyond with the audio doesn't pick up and you have located
??? the trouble.
Farhan, thanks for replying, thanks for your patience.?? Here are the
responses to your thoughts:
audio preamp might be busted.
/*Uh-Oh!? Q16?
*/
the LM386 seems to be working (from the test that you performed). check
the voltages around the audio preamp's base and collector.
/*base: 0.7v?? collector: 1.6v?? emitter: 0v
*/
if the LM386 gives you noise,
/*just touching pin3 no longer gives noise, injecting a 1KHz audio tone
0dB there does appear out the speaker, the 386 is amplifying
*/
does the volume control give you noise too?
*/just touching middle lug no longer gives noise, injecting a 1KHz audio
tone 0dB there does appear out the speaker/*/, the 386 is amplifying/*/
/*
trace the connectivity from pin 3 of the LM386 to the volume control's
middle lug.
/*there is direct connection
*/
if the noise ensues when you touch a wire to the middle lug of the
volume control,
/*there is no noise touching wire here nor anywhere else
*/
then move to the upper lug (not the one connected to the ground),
/*there is no noise touching wire here nor anywhere else
*/
if that works, then, check at the collector of the audio preamp.
/*no noise there either
*/
essentially, you hve to get to the point beyond with the audio doesn't
pick up and you have located the trouble.
/*I agree, but there is no audio anywhere apparently*/
Given all this, should I attempt to replace Q16, audio pre-amp?
?Watching your troubleshooting video, I ran into immediate fail starting
with touching the back of the BNC antenna connector - silence! Then
silence at each and every point that you highlight.? But yet the
transmitter works!
-KG6PO
