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Bitx40 - Not Transmitting #bitx40help #bitx40

Gary.ingle@...
 

Bitx40 - was working, but now does not transmit audio.

The device was working well with many QSOs on 40m.
All of a sudden it does not transmitt any audio.
Receiving is excellent.

To test or trouble shoot I did the following.
I attached a rf power meter to the rf out and noted that on transmission the needel jumped up initially and immediatly dropped to nil.
I suspected the microphone so I replaced it and got the same result.

It seems as though the audio is not getting into the system to trigger the carrier signal and trigger the transmitter.
(I have very limited knoledge so may be off, but this is my assumption)

I also replaced the main board (not audrino and LCD) as I had a spare - same results

Does any one have any ideas on what to test or how to trouble shoot further.

Regards
Gary
ZS5GI

Jerry Gaffke
 

That sounds like a broken mike connector.

Since it receives, the si5351 on the Raduino is doing everything it needs to on transmit.

When the Bitx40 transmits, it switches off power to the receiver audio amp
and turns on power to the transmitter audio amp for the mike.
This switching of power causes a quick surge of audio signal into the modulator
as the caps charge, and causes the characteristic Bitx pop which you see
on the meter.  So the transmitter is working from the modulator on out to the antenna.
All that's left is the mike amp, the mike, and the wires between.

Since you replaced the main board (and thus the mike amp) and also replaced the mike,
that leaves us with just the wires between.  Or perhaps you now have two bad mikes?

Could try driving the mike amp (or even the modulator directly) with some other source of audio.
Mike amp wants to see maybe 50mv pk-to-pk going in from the mike.

Jerry, KE7ER


On Thu, Dec 27, 2018 at 10:53 PM, <Gary.ingle@...> wrote:
Bitx40 - was working, but now does not transmit audio.

The device was working well with many QSOs on 40m.
All of a sudden it does not transmitt any audio.
Receiving is excellent.

To test or trouble shoot I did the following.
I attached a rf power meter to the rf out and noted that on transmission the needel jumped up initially and immediatly dropped to nil.
I suspected the microphone so I replaced it and got the same result.

It seems as though the audio is not getting into the system to trigger the carrier signal and trigger the transmitter.
(I have very limited knoledge so may be off, but this is my assumption)

I also replaced the main board (not audrino and LCD) as I had a spare - same results

Does any one have any ideas on what to test or how to trouble shoot further.

Regards
Gary
ZS5GI

Gary.ingle@...
 

Thank you , Jerry.

I am going to try a completly new mike, including the wires to the jumper on the main board.

I also thought that I could try a CW transmission test if I wire up the CW keyer. ???

PS with regards to the Pop sound that when transmitting, it is not as loud as it used to be.
When i key the PTT it does switch off the receiving and I can hear a sort of a click sound as the speaker goes quiet.
I suppos this is because the audio transmitt is not making it through.

Thank you for your help so far.

I am a beginner on the electronics side with only self taught skills.

73
Gary
ZS5GI

Timothy Fidler
 

Gary , JG has done a v good job of pointing out where you are at the moment. My tuppence worth and this is not very systematic is that if relay K1 has failed or the PTT line is not getting earthed properly  then you would see Rx and no Tx.  This could be from the relay not getting power or the relay failing in the coil (or mechanically) or  one of the components across the relay coil being in partial short and stealing power from the coil (unlikely as for this to be valid there would have to be a common decent resistance somewhere to cause the voltage to pull down.... but then this is all magic - it worked, it don't work. Electrons have changed their mind) .   You could first check power is avail to the relay K1 (not K2)

http://www.hfsignals.com/index.php/2017/11/23/bitx40-circuit-description/

And if it is then put a screwdriver on the case and to your ear  and listen to  hear it pull in as PTT goes low.  (this crudity  avoids probing the PCB too much ) .  My guess is it may not.  If it does then you need to check the Tx  line is getting power.  If yes, then it was a good idea at the time and the best idea is to fish around on the site in particular the repository run by Mike to see where the list of voltage test points and voltages is.  Mostly these relate to uBitx but you might find a Bitx40 one.   Good luck 

Timothy Fidler
 

On second thoughts, you replaced the main  board ( I re read earlier post) . The chance of having two bad K1 relays seems remote - depending on what voltage you are running the thing on and how much use they have had.

2. Bear in mind ONLY a electret,  aka ceramic mike insert will work with this Bitx40 board as it stands.  If you replaced the microphone with a dynamic microphone as part of the testing ,  it won't work. (The circuit feeds out a low dc voltage to the microphone insert which the Dynamic Microphone does NOT want to see.) If you went.  Problem - > change to Dyna mike,  Problem remains,  ->change out PCB but retain second mike , I can see  where this is heading. (?)

Gary.ingle@...
 

Thank you , Timothy

I am not using a Dynamic mike, I am using the small electret mike as was supplied with the kit.
I make up the mic with a plastic enclosure and a switch for the PTT.
4 wires, 2 for the PTT and 2 for the Mic.

Just a thought - how important is polarity on the mic ? (could it be that I have switched the Pos and Neg ??)

Have been running the rig on a 13.8 DCV regulated power supply with a 2amp fuse.

Jakobus van der Merwe
 

Yes it is polarity concious. If you look at the capsule 2 connection pads, you will see that one of them have tracks to the casing. That is the negative one. The one that has no tracks to the casing is the positive one. 


On Fri, 28 Dec 2018, 11:16 Gary.ingle via Groups.Io <Gary.ingle=icloud.com@groups.io> wrote:
Thank you , Timothy

I am not using a Dynamic mike, I am using the small electret mike as was supplied with the kit.
I make up the mic with a plastic enclosure and a switch for the PTT.
4 wires, 2 for the PTT and 2 for the Mic.

Just a thought - how important is polarity on the mic ? (could it be that I have switched the Pos and Neg ??)

Have been running the rig on a 13.8 DCV regulated power supply with a 2amp fuse.

Gary.ingle@...
 

Thank you, Jakobus

I am at the office at the moment.
I will check polarity as soon as i get home

Regards

Gary
ZS5GI

Timothy Fidler
 

Polarity it critical.

There is a small Linear IC equiv approx to  a u741 built into the mic insert.   Generally one of the mic solder tabs on the back will  be marked with a posittive to show correct polarity. Your mileage may vary.

If the mic insert has been reverse powered it may be toasted (there are ways to test this depending on what test gear you have) .  It may well depend on the manufacturer. Some may install a protection diode, some not.

If you wired it  exactly the same way as the previous insert assuming the back solder tabs looked the same you should be fine - they are generally build to the same pattern.  Unless you have photos of what you did originally Red to which terminal etc,  it is surprising how tricky memory can be. 

 

Timothy E. Fidler : Engineer BE Mech(1) Auckland , NDT specialist AINDT UT /RT3 , MT2 CB #2885, 
Telephone Whangarei   022  691 8405
e: Engstr@...



----- Original Message -----
From:
BITX20@groups.io

To:
<BITX20@groups.io>
Cc:

Sent:
Fri, 28 Dec 2018 01:16:00 -0800
Subject:
Re: [BITX20] Bitx40 - Not Transmitting #bitx40help #bitx40


Thank you , Timothy

I am not using a Dynamic mike, I am using the small electret mike as was supplied with the kit.
I make up the mic with a plastic enclosure and a switch for the PTT.
4 wires, 2 for the PTT and 2 for the Mic.

Just a thought - how important is polarity on the mic ? (could it be that I have switched the Pos and Neg ??)

Have been running the rig on a 13.8 DCV regulated power supply with a 2amp fuse.

Timothy Fidler
 

On a related matter, the  heat sink of the IRF 510 on this tcvr and also on the uBitx  is live to ground ( It's a feature !!) Bear that in mind when working on it or casing it.  The Fuse on the supply line is good but it is likely the IRF will be destroyed first if the heat sink touches ground (current will flow  from the PSU to the Drain , out the tab on the case ,the Heat sink and to GND).  

Gary.ingle@...
 

Thank you, Timothy

It seems that the mic may be the underlying cause and if I have connected it in reverse polarity I may have damaged it.
Then testing with a damaged mic has invalidated all the tests performed
I will go and purchase a new one as they are quite cheap (ZAR 12)
I will double check the polarity on connecting it up.

Thank you for the tip on the positive heat sink.

 

Electret and Ceramic are two different types AFAIK. Electret is not AKA ceramic.


At 28-12-18, you wrote:

On second thoughts, you replaced the main  board ( I re read earlier post) . The chance of having two bad K1 relays seems remote - depending on what voltage you are running the thing on and how much use they have had.

2. Bear in mind ONLY a electret,  aka ceramic mike insert will work with this Bitx40 board as it stands.  If you replaced the microphone with a dynamic microphone as part of the testing ,  it won't work. (The circuit feeds out a low dc voltage to the microphone insert which the Dynamic Microphone does NOT want to see.) If you went.  Problem - > change to Dyna mike,  Problem remains,  ->change out PCB but retain second mike , I can see  where this is heading. (?)

Gary.ingle@...
 

Hooray  !!!  Thank you all for the assistance.

The root cause was connecting the mic with the wrong polarity.

A new mic and correct polarity connection and I am sorted.

I have learned a valuable lesson, thank you all

Gary

Timothy Fidler
 

Which is to say the old mike failed then you put a new one in with wrong polarity ? 
 

Timothy E. Fidler : Engineer BE Mech(1) Auckland , NDT specialist AINDT UT /RT3 , MT2 CB #2885, 
Telephone Whangarei   022  691 8405
e: Engstr@...



----- Original Message -----
From:
BITX20@groups.io

To:
<BITX20@groups.io>
Cc:

Sent:
Fri, 28 Dec 2018 09:41:53 -0800
Subject:
Re: [BITX20] Bitx40 - Not Transmitting #bitx40help #bitx40


Hooray  !!!  Thank you all for the assistance.

The root cause was connecting the mic with the wrong polarity.

A new mic and correct polarity connection and I am sorted.

I have learned a valuable lesson, thank you all

Gary