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Receiver Dead

Ken Macy
 

When I first set up the Bitx40, it did seem to receive OK. ?Then there began to be various, random ¡°drop outs¡± into silence.? Cycling the power usually got it back.? Then one day it went dead and never came back.? There was noise from the speaker when touching pin3 of the LM386, or where pin3 is connected to the volume pot.? Now it doesn¡¯t even do that.? The only output is when LM386 pin3 is fed a 0 dB 1KHz audio tone; the audio amp seems to work.?

?

The Raduino, DDS and display seem to be working, also the transmitter works!?

?

While sitting there being quiet, it draws 170ma, which seems high.?

?

I¡¯ve reviewed Farhan¡¯s troubleshooting video and I get no noise whatever at any of the points in the circuit he points out.? Measuring voltage at the points shown in the table by K7AGE all match what he lists there.

?

I¡¯ve read pages and pages of postings here and I haven¡¯t read anything close to this.? Any help on where to look next is welcome.

Ken, KG6PO
 

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.

- f

On Mon, Oct 2, 2017 at 12:23 AM, Ken Macy <kmacy@...> wrote:

When I first set up the Bitx40, it did seem to receive OK.? Then there began to be various, random ¡°drop outs¡± into silence.? Cycling the power usually got it back.? Then one day it went dead and never came back.? There was noise from the speaker when touching pin3 of the LM386, or where pin3 is connected to the volume pot.? Now it doesn¡¯t even do that.? The only output is when LM386 pin3 is fed a 0 dB 1KHz audio tone; the audio amp seems to work.?

?

The Raduino, DDS and display seem to be working, also the transmitter works!?

?

While sitting there being quiet, it draws 170ma, which seems high.?

?

I¡¯ve reviewed Farhan¡¯s troubleshooting video and I get no noise whatever at any of the points in the circuit he points out.? Measuring voltage at the points shown in the table by K7AGE all match what he lists there.

?

I¡¯ve read pages and pages of postings here and I haven¡¯t read anything close to this.? Any help on where to look next is welcome.

Ken, KG6PO
Ken Macy
 

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?
?
Vince Vielhaber
 

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

--
Michigan VHF Corp.

William Kimber
 

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.

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
Ken Macy
 

Vince

I do have a scope.
KG6PO
Michael Davis
 

I too had intermittent receive. I used the very non-technical "tap" method. One of the tiny toroids had a problem either in the winding or the soldered connections. I tapped/wiggled it so that it worked, re-soldered the connections, (which didn't fix it) then glued the toroid to stabilize it. It's been fine ever since. I don't remember which toroid it was. Tap and move each one slightly while listening for signals.

Sent from Mike's iPad WA1MAD
 


I'd definitely try to remember which toroid it was.
My guess is that the insulation on the magnet wire wasn't quite properly removed,
and you have a very flaky solder joint there, waiting to fail again.


On Sun, Oct 1, 2017 at 06:31 pm, Michael Davis wrote:
re-soldered the connections, (which didn't fix it) then glued the toroid to stabilize it. It's been fine ever since.
Vince Vielhaber
 

Excellent! Use that to follow each step thru the audio with an antenna connected to it. Doesn't matter what it's receiving, even noise will show an ever increasing waveform. Actually noise is preferred in this case.

Vince.

On 10/01/2017 09:16 PM, Ken Macy wrote:
Vince

I do have a scope.
KG6PO
--
Michigan VHF Corp.

 

I would imagine the vol control is suspect at this time...
- f

On 2 Oct 2017 7:48 am, "Vince Vielhaber" <vev@...> wrote:
Excellent!? Use that to follow each step thru the audio with an antenna connected to it.? Doesn't matter what it's receiving, even noise will show an ever increasing waveform.? Actually noise is preferred in this case.

Vince.



On 10/01/2017 09:16 PM, Ken Macy wrote:
Vince

I do have a scope.
KG6PO


--
? Michigan VHF Corp.? ?? ?
? ? ? ? ? ? ? ? ? ? ? ? ?



 

... or wired AAF (Kiwi slang, arse-about-face). Measure your pot wiper-to-each-end. Rotate shaft to 'minimum' as though (or if, then as) mounted in panel. Now which end measures 0 ohms? That's the end that goes to 'earth'/0V (the black wire on Farhan's hfsigs Wire Up picture).
 

Dexter,
It went dead over time. Looks like the horrible volume control have up the ghost.
- f

On 2 Oct 2017 8:45 am, "Dexter N Muir" <dexy@...> wrote:
... or wired AAF (Kiwi slang, arse-about-face). Measure your pot wiper-to-each-end. Rotate shaft to 'minimum' as though (or if, then as) mounted in panel. Now which end measures 0 ohms? That's the end that goes to 'earth'/0V (the black wire on Farhan's hfsigs Wire Up picture).

 

My first BITX40 #66 the volume control failed. The failure happened when I resoldered one lead that came off.
The plating quality is not good IMHO.

Check the DC voltage on LM386 pin 6. The degeneration leads me to think R111 or D18 failed.

Raj

At 02/10/2017, you wrote:

I would imagine the vol control is suspect at this time...
- f

On 2 Oct 2017 7:48 am, "Vince Vielhaber" <vev@...> wrote:
Excellent!?? Use that to follow each step thru the audio with an antenna connected to it.?? Doesn't matter what it's receiving, even noise will show an ever increasing waveform.?? Actually noise is preferred in this case.

Vince.



On 10/01/2017 09:16 PM, Ken Macy wrote:
Vince

I do have a scope.
KG6PO
Ken Macy
 

OK Everyone, thanks. ?I'll go back to bench with these pointers.
Ken, KG6PO
 

Ken KG6PO wrote..

If the LM386 and the volume control check out OK,
perhaps you could check out the relay connection
between M1 & M2. On the drawing, the relay contacts
are down in the lower right corner, part of the
antenna change-over relay.

--
73 Keith VE7GDH

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