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VOX Lockup

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John Huffman-2

VOX Lockup

I'm using a new microphone with my K2/100. It's a desk mike (Ten Tec 706) and
I'm using the VOX a lot more than in the past. Had a strange thing happen last
night.

The band was 75 meters and I had the attenuator on and the RF gain backed off by
about 75%.

The VOX worked fine during my net transmission. However, afterward I was
listening and a strong station seemed to trigger the VOX. I unplugged the mic,
but the K2 stayed in transmit mode. I had to turn off the K2 to stop
transmitting.

I know the K2 VOX doesn't have anti-VOX, but I was wearing headphones. Nothing
was coming through the speaker.

Any similar experiences or solutions?

73 de NA8M
John

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Don Wilhelm-3

RE: VOX Lockup

John,

The lockup condition might have been from some errant path created by a
firmware glitch - in which case, it will not likely happen again. But it
may be prudent to arbitrarily re-seat the socketed firmware chips (following
proper anti-static procedures).

If it should repeat itself, I would recommend that you look for the bad
solder connection. From the information available it is difficult to
speculate on where that probem area may happen to be - more data is
required.

73,
Don W3FPR

> -----Original Message-----
>
> I'm using a new microphone with my K2/100. It's a desk mike (Ten
> Tec 706) and
> I'm using the VOX a lot more than in the past. Had a strange
> thing happen last
> night.
>
> The band was 75 meters and I had the attenuator on and the RF
> gain backed off by
> about 75%.
>
> The VOX worked fine during my net transmission. However, afterward I was
> listening and a strong station seemed to trigger the VOX. I
> unplugged the mic,
> but the K2 stayed in transmit mode. I had to turn off the K2 to stop
> transmitting.
>
> I know the K2 VOX doesn't have anti-VOX, but I was wearing
> headphones. Nothing
> was coming through the speaker.
>
> Any similar experiences or solutions?
>
> 73 de NA8M
> John
>
>

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Stewart Baker

Re: VOX Lockup

In reply to this post by John Huffman-2

Hi John,

I had a similar problem a while back, where, after a time when triggered the VOX
would stay on. I finally traced the problem to a defective DAC IC (U2 MAX522).
This supplies a threshold voltage to comparator U4. I found that the voltage out
of U2 pin 5 was drifting with temperature. Eventually it got so close to the
voltage out of U3 pin 7 that ,when triggered the VOX locked up.
Fitting a new IC cured the problem.

To help you identify whether this is your problem, here are some voltage
measurements from my KSB2. These are the differential voltage readings
between U4 pins 2 & 3.

SSBA =1 =76mV
SSBA =2 =74mV
SSBA =3 =50mV

73
Stewart G3RXQ

On Sat, 31 Dec 2005 07:19:46 -0500, John Huffman wrote:

> I'm using a new microphone with my K2/100. It's a desk mike (Ten Tec 706) and
>
> I'm using the VOX a lot more than in the past. Had a strange thing happen
> last
> night.
>
> The band was 75 meters and I had the attenuator on and the RF gain backed off
> by
> about 75%.
>
> The VOX worked fine during my net transmission. However, afterward I was
> listening and a strong station seemed to trigger the VOX. I unplugged the
> mic,
> but the K2 stayed in transmit mode. I had to turn off the K2 to stop
> transmitting.
>
> I know the K2 VOX doesn't have anti-VOX, but I was wearing headphones.
> Nothing
> was coming through the speaker.
>
> Any similar experiences or solutions?
>
> 73 de NA8M
> John
>
>
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>
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> Elecraft web page: http://www.elecraft.com

John Huffman-2

Re: VOX Lockup

Stewart and Don and anyone else -

I've gotten back to trying to fix my VOX. It seems that with any microphone the
VOX wants to key the radio until shut off. Sometimes right away, sometimes
after a bit. Disconnecting the microphone doesn't help. PTT works fine.

I have followed Don's advice and reseated the firmware chip - no joy.

I followed Stewart's advice and measured the voltage between pins 2 and 3 on U4.
He suggested:

> SSBA =1 =76mV
> SSBA =2 =74mV
> SSBA =3 =50mV

I got 3.1v at all settings.

I then checked the voltages on all pin U4 pins according to the manual. All are
close with one minor and one major exception.

Minor - pin 6 reads 5.7v instead of manual listed 5.1v.

Major - pin 3 reads 5.97v instead of manual listed .6v.
And, once the PTT is pressed and released, pin 3 reads 3.1v regardless of SSBA
or SSBC setting. It then remains at 3.1v

Where to next, oh Gurus?

73 de NA8M
John

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Stewart Baker

Re: VOX Lockup

John,

Please re-measure the voltagesBETWEEN pins 2 and 3 on U4.
If it is still 3.1v then you have really got problems, and the VOX should not
work at all.

73
Stewart G3RXQ

On Sat, 7 Jan 2006 09:40:29 -0500, John Huffman wrote:

> I followed Stewart's advice and measured the voltage between pins 2 and 3 on
> U4.
> He suggested:
>
>> SSBA =1 =76mV
>> SSBA =2 =74mV
>> SSBA =3 =50mV
>>
> I got 3.1v at all settings.
>

John Huffman-2

Re: VOX Lockup

Stewart -

Remeasured. Between pins 2 and 3 I get 3.6v. But, if I press and release the
PTT, it goes to .8v. It remains at .8v regardless of SSBA setting.

73 de NA8M
John

> Please re-measure the voltagesBETWEEN pins 2 and 3 on U4.

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Stewart Baker

Re: VOX Lockup

John,

If you are on PTT and have the PTT pressed then the voltage on U4 pin 3 will be
< 0.6v.

If the voltage on U2 pin 2 is around 2.2v then when VOX operation is selected
then PIC U1 measures this voltage from the COMP OUT signal on U1 pin 3 and
commands the DAC U2 to output a similar voltage to U4 pin 3. i.e 2.2v.

I would check that the voltage on U1 pin 3 is the same as on U4 pin 2.
If that is OK, then check all the soldered connections between U1 and U2.

Then I would look at replacing U2 as it does not seem to be giving out the
correct levels either for PTT (0.8V vs 0.6V), or for VOX (3.1V vs 2.2V).

Hope this helps

73
Stewart G3RXQ

On Sat, 7 Jan 2006 09:55:28 -0500, John Huffman wrote:
> Stewart -
>
> Remeasured. Between pins 2 and 3 I get 3.6v. But, if I press and release the
> PTT, it goes to .8v. It remains at .8v regardless of SSBA setting.
>
> 73 de NA8M
> John
>
>> Please re-measure the voltagesBETWEEN pins 2 and 3 on U4.

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