K2 Distorted receive audio and low power output

[Denis Jackson-2]

My K2 hasn't been used for a few years but, with the intention of taking it
out for a bit of SOTA work, I powered it up today.  Alas, I have a problem.

 

The receive audio is intermittently distorted on all modes.  With a constant
carrier, it sounds like there is a warble to the note.  There is another
problem in that it has is that the RF power output is only about 6 watts
(it's the 15W version) and that seems constant on all bands.  I don't think
these two problems are related because the power is always low regardless of
whether the audio is distorted or not but thought it worth mentioning
nonetheless

 

Any suggestions as to where to start looking for the cause of the RX
distortion?  

 

73

 

Denis MW0CBC / GW8OQV

 

 



---
This email has been checked for viruses by Avast antivirus software.
https://www.avast.com/antivirus
______________________________________________________________
Elecraft mailing list
Home: http://mailman.qth.net/mailman/listinfo/elecraft
Help: http://mailman.qth.net/mmfaq.htm
Post: mailto:[hidden email]

This list hosted by: http://www.qsl.net
Please help support this email list: http://www.qsl.net/donate.html
Message delivered to [hidden email]

[Don Wilhelm]

Denis,

Do you have the KDSP2 installed in your K2?  If so, check the DSP NR.
If it is on, it can cause distortion.  It does an effective job of
reducing noise, but does introduce some distortion - and may appear
intermittent depending on the signals and their level.

If no KDSP2, then check the soldering in the PLL Reference area as well
as the BFO area.  Marginal solder connections may have been OK in the
past, but can fail after time.  Check the schematic for components in
those areas and re-flow the soldering.

You can also do the Receive Signal Tracing as indicated in the manual.
You may have to connect a strong signal generator as described in the
Troubleshooting section of the manual.  An XG1 or XG2 will not provide a
strong enough signal (the XG3 will), so construct the oscillator shown
in the troubleshooting section of the manual.

The power output problem may or may not be related.  The best way to
find the offending stage is to do Transmit Signal Tracing as described
in the Troubleshooting manual appendix.  When you get to a stage which
produces less than the expected values, that is the output of the
failing stage, and you can investigate that particular stage for the
problem.  Re-flowing the soldering may correct it.
Component failure is not the most common cause of failure (soldering
is), so do not jump to conclusions about a component being bad -
exception is if one of the PA transistors has been damaged.  If you find
everything up to the PA transistor bases OK, then replacement of the PA
transistors with the K2PAKIT from Elecraft may be in order.

73,
Don W3FPR

On 4/26/2017 5:19 PM, Denis Jackson wrote:

> My K2 hasn't been used for a few years but, with the intention of taking it
> out for a bit of SOTA work, I powered it up today.  Alas, I have a problem.
>
> The receive audio is intermittently distorted on all modes.  With a constant
> carrier, it sounds like there is a warble to the note.  There is another
> problem in that it has is that the RF power output is only about 6 watts
> (it's the 15W version) and that seems constant on all bands.  I don't think
> these two problems are related because the power is always low regardless of
> whether the audio is distorted or not but thought it worth mentioning
> nonetheless

______________________________________________________________
Elecraft mailing list
Home: http://mailman.qth.net/mailman/listinfo/elecraft
Help: http://mailman.qth.net/mmfaq.htm
Post: mailto:[hidden email]

This list hosted by: http://www.qsl.net
Please help support this email list: http://www.qsl.net/donate.html
Message delivered to [hidden email]

[Denis Jackson-2]

Hi Don,

Many thanks for this sound advice.

There is a KDSP2 installed and I found an old post of yours referring to its potential to cause distortion and had therefore already turned NR off and set it to bypass.  Alas, it made no difference to the characteristics of the problem.

I have an old HP signal generator here but the problem seems so intermittent it's going to be challenging to get to the bottom if re-flowing the solder joints doesn't do the trick.  I've been in my shack/office for a couple of hours now and the problem has come and gone more times than I can count.  I am out on site (I'm a consultant biologist/ecologist and work some strange hours) over tonight and most of tomorrow but I should have some time over the weekend to at least make a start and will post again when I have made some progress - one way or another!

73

Denis MW0CBC / GW8OQV

-----Original Message-----
From: Don Wilhelm [mailto:[hidden email]]
Sent: 26 April 2017 22:51
To: Denis Jackson; [hidden email]
Subject: Re: [Elecraft] K2 Distorted receive audio and low power output

Denis,

Do you have the KDSP2 installed in your K2?  If so, check the DSP NR.
If it is on, it can cause distortion.  It does an effective job of reducing noise, but does introduce some distortion - and may appear intermittent depending on the signals and their level.

If no KDSP2, then check the soldering in the PLL Reference area as well as the BFO area.  Marginal solder connections may have been OK in the past, but can fail after time.  Check the schematic for components in those areas and re-flow the soldering.

You can also do the Receive Signal Tracing as indicated in the manual.
You may have to connect a strong signal generator as described in the Troubleshooting section of the manual.  An XG1 or XG2 will not provide a strong enough signal (the XG3 will), so construct the oscillator shown in the troubleshooting section of the manual.

The power output problem may or may not be related.  The best way to find the offending stage is to do Transmit Signal Tracing as described in the Troubleshooting manual appendix.  When you get to a stage which produces less than the expected values, that is the output of the failing stage, and you can investigate that particular stage for the problem.  Re-flowing the soldering may correct it.
Component failure is not the most common cause of failure (soldering is), so do not jump to conclusions about a component being bad - exception is if one of the PA transistors has been damaged.  If you find everything up to the PA transistor bases OK, then replacement of the PA transistors with the K2PAKIT from Elecraft may be in order.

73,
Don W3FPR

On 4/26/2017 5:19 PM, Denis Jackson wrote:

> My K2 hasn't been used for a few years but, with the intention of
> taking it out for a bit of SOTA work, I powered it up today.  Alas, I have a problem.
>
> The receive audio is intermittently distorted on all modes.  With a
> constant carrier, it sounds like there is a warble to the note.  There
> is another problem in that it has is that the RF power output is only
> about 6 watts (it's the 15W version) and that seems constant on all
> bands.  I don't think these two problems are related because the power
> is always low regardless of whether the audio is distorted or not but
> thought it worth mentioning nonetheless

---
This email has been checked for viruses by Avast antivirus software.
https://www.avast.com/antivirus

______________________________________________________________
Elecraft mailing list
Home: http://mailman.qth.net/mailman/listinfo/elecraft
Help: http://mailman.qth.net/mmfaq.htm
Post: mailto:[hidden email]

This list hosted by: http://www.qsl.net
Please help support this email list: http://www.qsl.net/donate.html
Message delivered to [hidden email]