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K2 SSB, "Hi Cur" message on PTT

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Doug Heacock

K2 SSB, "Hi Cur" message on PTT

I dusted off my old K2 recently and decided to try to wire up an electret
mic and give SSB a try--I've had the SSB module since I built the K2 years
ago, but just never used it, because I had no mic at the time. I've
discovered that when I ground the PTT line with the K2 in LSB or USB mode, I
get the "Hi Cur" message, and my output power goes to well over 15W,
regardless of the setting of the power output control.

I've done some of the voltage checks recommended in the SSB module manual,
but only those for RX mode--I'm a little nervous about trying to measure
voltages in transmit mode, because I don't know how long the PA can take
that kind of current, and I don't want to fritz the final or cause other
problems. There are some voltage discrepancies associated with U2--pin 5 on
that device is supposed to have 0.6v in RX mode, but I'm seeing more like
2.5v. Pin 3 of U4--same story.

If anyone out there has any suggestions for where to look for problems, or
how to do further testing, I'm all ears. I found an old thread in the list
archives that suggested replacing Q3 and/or Q4 on the K2 control board, in
case one of those 2N7000s happened to take a static electricity hit, but I
haven't had a chance to do that yet (don't have any 7000s lying around), and
I'm somewhat hesitant to go down that path because this rig seems to work
just fine in CW mode.

Many thanks, Doug
--
Doug Heacock
AA0MS
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Don Wilhelm-4

Re: K2 SSB, "Hi Cur" message on PTT

Doug,

Start with the easy things first - it could be RF Feedback or some type
of oscillation in the mic itself - or it could be a lack of carrier
balance on the KSB2 board. To check quickly, do not connect a
microphone at all - just connect your paddles to the key jack, and in
SSB mode, close the dot paddle (the DOT line inside the K2 is the same
as PTT). Do you have any power output? You should not because there is
no audio. If you do have RF output, the first step is to adjust the
carrier balance pot on the KSB2 board for minimum RF - you may have to
compromise between LSB and USB, but the carrier level should drop to a
very low level at the correct adjustment point. That point should be
near mid-range on the pot, if it is not, then look for a problem.
Once you have the carrier balanced, it is time to try the microphone
again - since you now know the carrier balance is correct, this time
suspect RF Feedback (or audio feedback if you have a computer soundcard
also connected) if it happens when the mic is added.

There are other possibilities such as a problem in the ALC section of
the KSB2 board, but try the above before doing anything else.

73,
Don W3FPR

Doug Heacock wrote:

> I dusted off my old K2 recently and decided to try to wire up an electret
> mic and give SSB a try--I've had the SSB module since I built the K2 years
> ago, but just never used it, because I had no mic at the time. I've
> discovered that when I ground the PTT line with the K2 in LSB or USB mode, I
> get the "Hi Cur" message, and my output power goes to well over 15W,
> regardless of the setting of the power output control.
>
> I've done some of the voltage checks recommended in the SSB module manual,
> but only those for RX mode--I'm a little nervous about trying to measure
> voltages in transmit mode, because I don't know how long the PA can take
> that kind of current, and I don't want to fritz the final or cause other
> problems. There are some voltage discrepancies associated with U2--pin 5 on
> that device is supposed to have 0.6v in RX mode, but I'm seeing more like
> 2.5v. Pin 3 of U4--same story.
>
> If anyone out there has any suggestions for where to look for problems, or
> how to do further testing, I'm all ears. I found an old thread in the list
> archives that suggested replacing Q3 and/or Q4 on the K2 control board, in
> case one of those 2N7000s happened to take a static electricity hit, but I
> haven't had a chance to do that yet (don't have any 7000s lying around), and
> I'm somewhat hesitant to go down that path because this rig seems to work
> just fine in CW mode.
>
> Many thanks, Doug
>
>

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K1LI

Re: K2 SSB, "Hi Cur" message on PTT

Doug,

I have owned and used my K2/100 on SSB and CW for almost 10 years, but it
has been relegated to "second radio" duty since getting my K3 a year ago.

I've been getting the K2 ready for a DXpedition for the last few days and I
have noticed a similar symptom to what you describe, as part of a
more-general syndrome that I can't explain and that is very unnerving.

The primary problem is that I frequently turn on the K2 in USB mode but I
can't get any output. Speaking into the mic simply doesn't produce any
output, doesn't move the ALC meter and doesn't produce anything I can hear
on the K3. Even though it all worked together fine the previous day.

As part of the diagnosis procedure, I removed the mic plug from the front
panel and shorted the PTT pin to the adjacent GND pin - I was going to see
if touching the MIC pin in this configuration would create output and
indicate a faulty line from the mic itself. Lo and behold, shorting the PTT
and GND pins produced a *strong* carrier, whose output I could vary with the
POWER control.

Since this didn't produce the expected result (to say the least!), I
remembered that the "dot" side of the paddle would act as PTT, so I plugged
in a paddle and got the same behavior.

Just for grins, I switched to CW and everything worked as expected.

Switching back to USB, it too now works as expected.

At some point in this procedure, I saw both the Hi Cur and the PA Hot
warnings, but both are gone now.

Don - any thoughts on what's going on here? Do I have to do a "reboot" of
the radio?

Brian K1LI
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Don Wilhelm-4

Re: K2 SSB, "Hi Cur" message on PTT

Brian,

Don't do a "re-boot" of the K2, it is not likely to solve anything and
will only lose your menu settings including the filter and PLL data.
You have an intermittent somewhere, most likely on the KSB2 board. I
have (only once or twice) seen an intermittent connection in the carrier
balance pot itself that could cause such "strange happenings". I would
suggest starting with re-flowing the solder on the KSB2 board in the
area of the carrier balance and balanced modulator stages, then
"crossing the fingers" that it does not re-occur.

The unfortunate part about intermittents is that it has to fail (and
stay failed) for one to troubleshoot it properly.

73,
Don W3FPR

Brian Machesney wrote:

> Doug,
>
> I have owned and used my K2/100 on SSB and CW for almost 10 years, but it
> has been relegated to "second radio" duty since getting my K3 a year ago.
>
> I've been getting the K2 ready for a DXpedition for the last few days and I
> have noticed a similar symptom to what you describe, as part of a
> more-general syndrome that I can't explain and that is very unnerving.
>
> The primary problem is that I frequently turn on the K2 in USB mode but I
> can't get any output. Speaking into the mic simply doesn't produce any
> output, doesn't move the ALC meter and doesn't produce anything I can hear
> on the K3. Even though it all worked together fine the previous day.
>
> As part of the diagnosis procedure, I removed the mic plug from the front
> panel and shorted the PTT pin to the adjacent GND pin - I was going to see
> if touching the MIC pin in this configuration would create output and
> indicate a faulty line from the mic itself. Lo and behold, shorting the PTT
> and GND pins produced a *strong* carrier, whose output I could vary with the
> POWER control.
>
> Since this didn't produce the expected result (to say the least!), I
> remembered that the "dot" side of the paddle would act as PTT, so I plugged
> in a paddle and got the same behavior.
>
> Just for grins, I switched to CW and everything worked as expected.
>
> Switching back to USB, it too now works as expected.
>
> At some point in this procedure, I saw both the Hi Cur and the PA Hot
> warnings, but both are gone now.
>
> Don - any thoughts on what's going on here? Do I have to do a "reboot" of
> the radio?
>
>
>

Doug Heacock

Re: K2 SSB, "Hi Cur" message on PTT

In reply to this post by Don Wilhelm-4

Thanks, Don--I do have the same symptoms when I connect paddles and hit the
dot paddle in SSB mode--I'll try the adjustment you recommended and keep
working at it.

73 de aa0ms

On Mon, Feb 8, 2010 at 6:08 PM, Don Wilhelm <[hidden email]> wrote:

> Doug,
>
> Start with the easy things first - it could be RF Feedback or some type of
> oscillation in the mic itself - or it could be a lack of carrier balance on
> the KSB2 board. To check quickly, do not connect a microphone at all - just
> connect your paddles to the key jack, and in SSB mode, close the dot paddle
> (the DOT line inside the K2 is the same as PTT). Do you have any power
> output? You should not because there is no audio. If you do have RF
> output, the first step is to adjust the carrier balance pot on the KSB2
> board for minimum RF - you may have to compromise between LSB and USB, but
> the carrier level should drop to a very low level at the correct adjustment
> point. That point should be near mid-range on the pot, if it is not, then
> look for a problem.
> Once you have the carrier balanced, it is time to try the microphone again
> - since you now know the carrier balance is correct, this time suspect RF
> Feedback (or audio feedback if you have a computer soundcard also connected)
> if it happens when the mic is added.
>
> There are other possibilities such as a problem in the ALC section of the
> KSB2 board, but try the above before doing anything else.
>
> 73,
> Don W3FPR
>
>
> Doug Heacock wrote:
>
>> I dusted off my old K2 recently and decided to try to wire up an electret
>> mic and give SSB a try--I've had the SSB module since I built the K2 years
>> ago, but just never used it, because I had no mic at the time. I've
>> discovered that when I ground the PTT line with the K2 in LSB or USB mode,
>> I
>> get the "Hi Cur" message, and my output power goes to well over 15W,
>> regardless of the setting of the power output control.
>>
>> I've done some of the voltage checks recommended in the SSB module manual,
>> but only those for RX mode--I'm a little nervous about trying to measure
>> voltages in transmit mode, because I don't know how long the PA can take
>> that kind of current, and I don't want to fritz the final or cause other
>> problems. There are some voltage discrepancies associated with U2--pin 5
>> on
>> that device is supposed to have 0.6v in RX mode, but I'm seeing more like
>> 2.5v. Pin 3 of U4--same story.
>>
>> If anyone out there has any suggestions for where to look for problems, or
>> how to do further testing, I'm all ears. I found an old thread in the
>> list
>> archives that suggested replacing Q3 and/or Q4 on the K2 control board, in
>> case one of those 2N7000s happened to take a static electricity hit, but I
>> haven't had a chance to do that yet (don't have any 7000s lying around),
>> and
>> I'm somewhat hesitant to go down that path because this rig seems to work
>> just fine in CW mode.
>>
>> Many thanks, Doug
>>
>>
>

--
Doug Heacock
Director of Media and Communications
Contemporary Worship Leader
Lawrence Free Methodist Church
Lawrence, KS
[hidden email]
http://www.lfmchurch.org
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