K2 - low power/reception on 80m

[Philippe-36]

Hi,

I bought an used K2/100 with an issue on 80m:

- RF is low (less than 1 watt) even when PWR set to 100W  

- reception sensibility is low as well, I need to switch the PRE to hear
something on the band.

- all other bands are doing fine (good sensibility, 100W+)

I first though about the band filter but I didn't success to get any RF
increase when re-tuning L3/L4.

Do you have an idea where I can start?

Thanks

--
Phil
F5IYJ / NK2F
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[vk2rq]

Sticky relay?

73, Matt VK2RQ




On Thu, Sep 29, 2016 at 5:32 PM +1000, "Philippe" <[hidden email]> wrote:










Hi,

I bought an used K2/100 with an issue on 80m:

- RF is low (less than 1 watt) even when PWR set to 100W  

- reception sensibility is low as well, I need to switch the PRE to hear
something on the band.

- all other bands are doing fine (good sensibility, 100W+)

I first though about the band filter but I didn't success to get any RF
increase when re-tuning L3/L4.

Do you have an idea where I can start?

Thanks

--
Phil
F5IYJ / NK2F
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[Don Wilhelm]

Phillippe,

There are several things that could be wrong.
First determine if it is a problem with the base K2 or the KPA100. To
accomplish that, you will have to physically remove the KPA100, unplug
the 4 cables and power the base K2 from the 2.1mm coaxial power jack on
the lower rear panel.

It could be the 80 meter Low pass Filter - either in the base K2 or the
KPA100 - badly tinned toroid leads are a common cause.  It is also
possible that the LPF relay or the BPF relay for 80 meters is not
working properly - look at K3 and K8 in the base K2 and K11 and K12 in
the KPA100.  If the relay case has been damaged, replace it.

73,
Don W3FPR

On 9/29/2016 3:31 AM, Philippe wrote:

> Hi,
>
> I bought an used K2/100 with an issue on 80m:
>
> - RF is low (less than 1 watt) even when PWR set to 100W
>
> - reception sensibility is low as well, I need to switch the PRE to hear
> something on the band.
>
> - all other bands are doing fine (good sensibility, 100W+)
>
>

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[Philippe-36]

Hi,
thanks Matt & Don for your messages.
The issue is located on the K2, not on the PA
I checked K3 and K8. K3 looks fine but it looks like I have a shortcut between the pins 7-8-9.
I will get another relay and change K8.

Thanks again
Cheers,
--
Phil
F5IYJ / NK2F

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[Don Wilhelm]

Phil,

Don't be too quick to draw that conclusion.
Note that everything in the Low Pass Filter will appear to be connected
to ground at DC.  If you want to make a valid DC resistance check, you
have to lift lead 4 of T4 and re-measure.

Good that you have isolated it to the base K2.
Take a good look at the toroid leads for L16 and L17.  You should not
see any enamel on the solder side and there should not be a ring around
the toroid leads - that is an indication that the lead was not properly
stripped and tinned.  In addition, there should be a bit of tinned lead
exposed on the component side.

It would be nice to know if the prior owner operated it on 80 meters.

The relays in the base K2 are latching type, so you can set to the band
of interest and then turn power off to make resistance readings at the
relay contacts.

73,
Don W3FPR

On 9/29/2016 6:29 PM, Philippe wrote:
> Hi,
> thanks Matt & Don for your messages.
> The issue is located on the K2, not on the PA
> I checked K3 and K8. K3 looks fine but it looks like I have a shortcut between the pins 7-8-9.
> I will get another relay and change K8.
>
>

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[Philippe-36]

On Thu, Sep 29, 2016 at 07:12:58PM -0400, Don Wilhelm wrote:
> Phil,
>
> Don't be too quick to draw that conclusion.
> Note that everything in the Low Pass Filter will appear to be connected to
> ground at DC.  If you want to make a valid DC resistance check, you have to
> lift lead 4 of T4 and re-measure.
>

Thanks Don.
You was right, the 2 relays are fine (tested after I lifted T4 lead 4 as suggested).
I checked also L16 and L17. I removed L17 because I wasn't sure it was properly stripped, and re-soldered it.
I still have an issue on RX and TX on 80m. :(

I need to go 'deeper'.

73,
Phil.

--
Philippe Givet
F5IYJ / NK2F
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[Don Wilhelm]

Phil,

The next logical step is to do Transmit Signal Tracing as described in
Appendix E of the manual.  Use 80 meters instead of 40.

When you come to the first point where the RF Voltage is substatially
less than the Expected value, that is the output of the problem stage.  
You can then examine the schematic to see the components associated with
that stage and evaluate each individually.

73,
Don W3FPR

On 10/1/2016 2:00 PM, Philippe wrote:
> On Thu, Sep 29, 2016 at 07:12:58PM -0400, Don Wilhelm wrote:
> I need to go 'deeper'.

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[Don Wilhelm]

Phil,

One thing you can easily and quickly check is that the VCO signal has
not gone out of range.
Set the K2 to 4000kHz and measure the left end of R30 - it should not be
above 7.5 volts (nearer to 6 volts is better).  Then tune to 3500kHz and
again measure the left end of R30 - it should not be below 1.5 volts.  
If it is within that range, the VCO is properly locking.

If it is not within that range, do the VCO Alignment as indicated in the
manual on page 64 (if the manual is older, you will find it on page 55).

73,
Don W3FPR

On 10/1/2016 2:00 PM, Philippe wrote:

> On Thu, Sep 29, 2016 at 07:12:58PM -0400, Don Wilhelm wrote:
>> Phil,
>>
>> Don't be too quick to draw that conclusion.
>> Note that everything in the Low Pass Filter will appear to be connected to
>> ground at DC.  If you want to make a valid DC resistance check, you have to
>> lift lead 4 of T4 and re-measure.
>>
> Thanks Don.
> You was right, the 2 relays are fine (tested after I lifted T4 lead 4 as suggested).
> I checked also L16 and L17. I removed L17 because I wasn't sure it was properly stripped, and re-soldered it.
> I still have an issue on RX and TX on 80m. :(
>
> I need to go 'deeper'.
>
> 73,
> Phil.
>

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[Philippe-36]

Thanks Don,

I measured at 4000KHz (5.87V) and at 3500KHz (1.85V) so it is within the
range you gave me. I need now to take my RF probe and go further.

Again, many thanks for the help you provided. Greatly appreciated.

73,

Phil.

On 02.10.2016 00:43, Don Wilhelm wrote:

> Phil,
>
> One thing you can easily and quickly check is that the VCO signal has not gone out of range.
> Set the K2 to 4000kHz and measure the left end of R30 - it should not be above 7.5 volts (nearer to 6 volts is better).  Then tune to 3500kHz and again measure the left end of R30 - it should not be below 1.5 volts.  If it is within that range, the VCO is properly locking.
>
> If it is not within that range, do the VCO Alignment as indicated in the manual on page 64 (if the manual is older, you will find it on page 55).
>
> 73,
> Don W3FPR
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