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K2: High SWR On Dummy Load

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ny4g

K2: High SWR On Dummy Load

My. K2/100 is acting up in that it is showing high SWR even on a dummy load. Any ideas on whether the K2 finals may be blown? It behaves the same way on all the bands. It displays high current with the power set to 3 watts or more. My K2 is SN7105.

Will appreciate diagnostic help.

Ariel NY4G

Sent from my iPad
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Jim Wiley

Re: K2: High SWR On Dummy Load

Ariel -

What options, if any, are in your K2? Can you temporarily disable the
100-watt PA and connect the 10-watt PA directly to the dummy load
(disconnecting the cables to the KPA-100 completely), and if so, what
happens then? It may be that the wattmeter diodes are damaged. If that
happens the power control circuit cannot operate properly and all sorts
of odd things may happen.

- Jim, KL7CC

On 10/24/2012 6:18 PM, Ariel Jacala wrote:

> My. K2/100 is acting up in that it is showing high SWR even on a dummy load. Any ideas on whether the K2 finals may be blown? It behaves the same way on all the bands. It displays high current with the power set to 3 watts or more. My K2 is SN7105.
>
> Will appreciate diagnostic help.
>
> Ariel NY4G
>
> Sent from my iPad
> ______________________________________________________________
> 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
>

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Vic Rosenthal

Re: K2: High SWR On Dummy Load

In reply to this post by ny4g

You probably have thought of this, but make sure you are using a different cable to the
dummy load than the one you were using with the antenna. Bad cables, or rather, bad
cable-connector junctions, are very common.

On 10/24/2012 7:18 PM, Ariel Jacala wrote:
> My. K2/100 is acting up in that it is showing high SWR even on a dummy load. Any ideas on whether the K2 finals may be blown? It behaves the same way on all the bands. It displays high current with the power set to 3 watts or more. My K2 is SN7105.
>
> Will appreciate diagnostic help.
>
> Ariel NY4G
>
> Sent from my iPad
>

--
Vic, K2VCO
Fresno CA
http://www.qsl.net/k2vco/

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Don Wilhelm-4

Re: K2: High SWR On Dummy Load

In reply to this post by ny4g

Ariel,

I would think your K2 finals are OK (for now).
My best guess is that you have a KPA100 and a static charge has damaged
diodes D16 and D17 in the KPA100. If you do not have the KPA100, then
you most likely have the KAT2 and the diodes are D1 and D2 - the same
principle applies.

To test my theory, connect an external wattmeter between the K2 and the
antenna. Set the power control to 2 watts and do a TUNE - what is the
power indicated by the external wattmeter? If it is substantially
higher than the set power, there is something wrong with the wattmeter
in the KPA100 (or KAT2) - replace the diodes.

Be aware that those diodes are damaged by a static charge on the
feedline. You should have a DC path across the feedline and the coax
shield should be grounded. In any case, install an antenna switch and
switch the K2 to a dummy load when not in use.

73,
Don W3FPR

On 10/24/2012 10:18 PM, Ariel Jacala wrote:
> My. K2/100 is acting up in that it is showing high SWR even on a dummy load. Any ideas on whether the K2 finals may be blown? It behaves the same way on all the bands. It displays high current with the power set to 3 watts or more. My K2 is SN7105.
>
> Will appreciate diagnostic help.
>
>

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ny4g

Re: K2: High SWR On Dummy Load

Thanks to Jim, Vic and Don for the return comments

I disconnected the KPA100 and put on the K2 top with the KAT2 ATU. With the K2 ATU connected and the dummy load connected - the SWR correctly reads 1:1 with menu set for CALS. With the menu set to CALP, the power levels appeared to modulate correctly with the PWR knob although this is an item i have to double check. With the ATU disconnected, the displayed power on tune differs from the power setting. This suggests to me that there is something wrong with the base K2. I still have to do what Don suggested about connection to an external watt meter.

Any additional ideas are welcome.

Ariel NY4G
Sent from my iPad

On Oct 25, 2012, at 8:21 AM, "Don Wilhelm" <[hidden email]> wrote:

> Ariel,
>
> I would think your K2 finals are OK (for now).
> My best guess is that you have a KPA100 and a static charge has damaged diodes D16 and D17 in the KPA100. If you do not have the KPA100, then you most likely have the KAT2 and the diodes are D1 and D2 - the same principle applies.
>
> To test my theory, connect an external wattmeter between the K2 and the antenna. Set the power control to 2 watts and do a TUNE - what is the power indicated by the external wattmeter? If it is substantially higher than the set power, there is something wrong with the wattmeter in the KPA100 (or KAT2) - replace the diodes.
>
> Be aware that those diodes are damaged by a static charge on the feedline. You should have a DC path across the feedline and the coax shield should be grounded. In any case, install an antenna switch and switch the K2 to a dummy load when not in use.
>
> 73,
> Don W3FPR
>
> On 10/24/2012 10:18 PM, Ariel Jacala wrote:
>> My. K2/100 is acting up in that it is showing high SWR even on a dummy load. Any ideas on whether the K2 finals may be blown? It behaves the same way on all the bands. It displays high current with the power set to 3 watts or more. My K2 is SN7105.
>>
>> Will appreciate diagnostic help.
>>
>>
>

Don Wilhelm-4

Re: K2: High SWR On Dummy Load

Ariel,

Do not be too quick to conclude that there is something wrong with the
base K2. The basic K2 uses only an RF voltage diode to display the
power output, and it may not be exact - it depends on the load and may
vary from band to band - if it only off by a watt or two, then all is OK
That is bypassed when the KAT2 or KPA100 is installed.

Yes, do check with the external wattmeter - both with and without the
KPA100. I still think KPA100 diodes D16 and D17 are highest on the
suspect list with other KPA100 wattmeter components being second on that
list.

73,
Don W3FPR

On 10/25/2012 11:18 AM, Ariel Jacala wrote:
> Thanks to Jim, Vic and Don for the return comments
>
> I disconnected the KPA100 and put on the K2 top with the KAT2 ATU. With the K2 ATU connected and the dummy load connected - the SWR correctly reads 1:1 with menu set for CALS. With the menu set to CALP, the power levels appeared to modulate correctly with the PWR knob although this is an item i have to double check. With the ATU disconnected, the displayed power on tune differs from the power setting. This suggests to me that there is something wrong with the base K2. I still have to do what Don suggested about connection to an external watt meter.
>

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ny4g

Re: K2: High SWR On Dummy Load

Don

The K2 with the ATU behaves as expected - internal meter agrees well with the external meter, current draw is as expected, and so forth for various power levels up to 10watts checked out. It was connected to a dummy load.

Without the ATU and the dummy load connected to the base K2 antenna, things are rather strange.... At 2 watts set on the power knob, output on the external meter is 2.7 watts and current draw is 0.96 amps; at a knob setting of 2.4 watts, output is up to 7 watts on the external meter and current draw is 1.4 amps; at a knob setting of 2.5 watts, power output is 10 watts and current draw is 1.96 amps; at 3 watts knob setting, I get the high current warning, and the external meter is pegged.

This leads me to believe that the base K2 is overdriving the KPA100. At low power settings - 5 watts, I was pegging the LEDs indicating power on the LDG100 autotuner, at over 125 watts.

Ariel NY4G

Sent from my iPad

On Oct 25, 2012, at 11:51 AM, "Don Wilhelm" <[hidden email]> wrote:

> Ariel,
>
> Do not be too quick to conclude that there is something wrong with the base K2. The basic K2 uses only an RF voltage diode to display the power output, and it may not be exact - it depends on the load and may vary from band to band - if it only off by a watt or two, then all is OK That is bypassed when the KAT2 or KPA100 is installed.
>
> Yes, do check with the external wattmeter - both with and without the KPA100. I still think KPA100 diodes D16 and D17 are highest on the suspect list with other KPA100 wattmeter components being second on that list.
>
> 73,
> Don W3FPR
>
> On 10/25/2012 11:18 AM, Ariel Jacala wrote:
>> Thanks to Jim, Vic and Don for the return comments
>>
>> I disconnected the KPA100 and put on the K2 top with the KAT2 ATU. With the K2 ATU connected and the dummy load connected - the SWR correctly reads 1:1 with menu set for CALS. With the menu set to CALP, the power levels appeared to modulate correctly with the PWR knob although this is an item i have to double check. With the ATU disconnected, the displayed power on tune differs from the power setting. This suggests to me that there is something wrong with the base K2. I still have to do what Don suggested about connection to an external watt meter.
>>
>

Don Wilhelm-4

Re: K2: High SWR On Dummy Load

Ariel,

You may indeed have a problem with D9 and the 3 associated resistors in
the base K2, BUT when the KAT2 or the KPA100 is installed, that circuit
is ignored.
Both the KAT2 and the KPA100 contain a true wattmeter that is positioned
right at the output and used for power control.

The K2 microprocessor reads the actual output and compares that to the
power knob setting. That result tells the microprocessor how to adjust
the drive. Unlike other ham transceivers, the K2 uses a closed loop to
control the power instead of simply adjusting the drive.

What that also means is that the wattmeter in the KPA100 is not working
(you have shown that the one in the KAT2 is working OK). As I indicated
before (and also indicated by your high SWR indication) there is a high
probability that KPA100 diodes D16 and D17 have been damaged.

When the diodes are damaged, the output back to the MCU is most likely
zero, and the MCU *thinks* there is no power output - it then increases
the drive to the maximum in an attempt to develop power. The result is a
HiCur warning and stress on the base K2 PA transistors.

Replace KPA100 D16 and D17 as the first order of business and after that
you can investigate any remaining problems. Note that those diodes can
be "half bad" and may show as good with a diode test - replacement is
the first order of business.

73,
Don W3FPR

On 10/25/2012 11:31 PM, Ariel Jacala wrote:

> Don
>
> The K2 with the ATU behaves as expected - internal meter agrees well with the external meter, current draw is as expected, and so forth for various power levels up to 10watts checked out. It was connected to a dummy load.
>
> Without the ATU and the dummy load connected to the base K2 antenna, things are rather strange.... At 2 watts set on the power knob, output on the external meter is 2.7 watts and current draw is 0.96 amps; at a knob setting of 2.4 watts, output is up to 7 watts on the external meter and current draw is 1.4 amps; at a knob setting of 2.5 watts, power output is 10 watts and current draw is 1.96 amps; at 3 watts knob setting, I get the high current warning, and the external meter is pegged.
>
> This leads me to believe that the base K2 is overdriving the KPA100. At low power settings - 5 watts, I was pegging the LEDs indicating power on the LDG100 autotuner, at over 125 watts.
>
> Ariel NY4G
>
> Sent from my iPad
>
> On Oct 25, 2012, at 11:51 AM, "Don Wilhelm" <[hidden email]> wrote:
>
>> Ariel,
>>
>> Do not be too quick to conclude that there is something wrong with the base K2. The basic K2 uses only an RF voltage diode to display the power output, and it may not be exact - it depends on the load and may vary from band to band - if it only off by a watt or two, then all is OK That is bypassed when the KAT2 or KPA100 is installed.
>>
>> Yes, do check with the external wattmeter - both with and without the KPA100. I still think KPA100 diodes D16 and D17 are highest on the suspect list with other KPA100 wattmeter components being second on that list.
>>
>> 73,
>> Don W3FPR
>>
>> On 10/25/2012 11:18 AM, Ariel Jacala wrote:
>>> Thanks to Jim, Vic and Don for the return comments
>>>
>>> I disconnected the KPA100 and put on the K2 top with the KAT2 ATU. With the K2 ATU connected and the dummy load connected - the SWR correctly reads 1:1 with menu set for CALS. With the menu set to CALP, the power levels appeared to modulate correctly with the PWR knob although this is an item i have to double check. With the ATU disconnected, the displayed power on tune differs from the power setting. This suggests to me that there is something wrong with the base K2. I still have to do what Don suggested about connection to an external watt meter.
>>>
> ______________________________________________________________
> 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
>

ny4g

Re: K2: High SWR On Dummy Load

Don and Group,

Thanks very much for the responses. I will look at the schematic and determine the associated resistors with D9 and replace it. I will also order KPA100 D16 and D17 diodes from Elecraft.

Ariel NY4G

> Date: Fri, 26 Oct 2012 08:10:37 -0400
> From: [hidden email]
> To: [hidden email]
> CC: [hidden email]
> Subject: Re: [Elecraft] K2: High SWR On Dummy Load
>
> Ariel,
>
> You may indeed have a problem with D9 and the 3 associated resistors in
> the base K2, BUT when the KAT2 or the KPA100 is installed, that circuit
> is ignored.
> Both the KAT2 and the KPA100 contain a true wattmeter that is positioned
> right at the output and used for power control.
>
> The K2 microprocessor reads the actual output and compares that to the
> power knob setting. That result tells the microprocessor how to adjust
> the drive. Unlike other ham transceivers, the K2 uses a closed loop to
> control the power instead of simply adjusting the drive.
>
> What that also means is that the wattmeter in the KPA100 is not working
> (you have shown that the one in the KAT2 is working OK). As I indicated
> before (and also indicated by your high SWR indication) there is a high
> probability that KPA100 diodes D16 and D17 have been damaged.
>
> When the diodes are damaged, the output back to the MCU is most likely
> zero, and the MCU *thinks* there is no power output - it then increases
> the drive to the maximum in an attempt to develop power. The result is a
> HiCur warning and stress on the base K2 PA transistors.
>
> Replace KPA100 D16 and D17 as the first order of business and after that
> you can investigate any remaining problems. Note that those diodes can
> be "half bad" and may show as good with a diode test - replacement is
> the first order of business.
>
> 73,
> Don W3FPR
>
> On 10/25/2012 11:31 PM, Ariel Jacala wrote:
> > Don
> >
> > The K2 with the ATU behaves as expected - internal meter agrees well with the external meter, current draw is as expected, and so forth for various power levels up to 10watts checked out. It was connected to a dummy load.
> >
> > Without the ATU and the dummy load connected to the base K2 antenna, things are rather strange.... At 2 watts set on the power knob, output on the external meter is 2.7 watts and current draw is 0.96 amps; at a knob setting of 2.4 watts, output is up to 7 watts on the external meter and current draw is 1.4 amps; at a knob setting of 2.5 watts, power output is 10 watts and current draw is 1.96 amps; at 3 watts knob setting, I get the high current warning, and the external meter is pegged.
> >
> > This leads me to believe that the base K2 is overdriving the KPA100. At low power settings - 5 watts, I was pegging the LEDs indicating power on the LDG100 autotuner, at over 125 watts.
> >
> > Ariel NY4G
> >
> > Sent from my iPad
> >
> > On Oct 25, 2012, at 11:51 AM, "Don Wilhelm" <[hidden email]> wrote:
> >
> >> Ariel,
> >>
> >> Do not be too quick to conclude that there is something wrong with the base K2. The basic K2 uses only an RF voltage diode to display the power output, and it may not be exact - it depends on the load and may vary from band to band - if it only off by a watt or two, then all is OK That is bypassed when the KAT2 or KPA100 is installed.
> >>
> >> Yes, do check with the external wattmeter - both with and without the KPA100. I still think KPA100 diodes D16 and D17 are highest on the suspect list with other KPA100 wattmeter components being second on that list.
> >>
> >> 73,
> >> Don W3FPR
> >>
> >> On 10/25/2012 11:18 AM, Ariel Jacala wrote:
> >>> Thanks to Jim, Vic and Don for the return comments
> >>>
> >>> I disconnected the KPA100 and put on the K2 top with the KAT2 ATU. With the K2 ATU connected and the dummy load connected - the SWR correctly reads 1:1 with menu set for CALS. With the menu set to CALP, the power levels appeared to modulate correctly with the PWR knob although this is an item i have to double check. With the ATU disconnected, the displayed power on tune differs from the power setting. This suggests to me that there is something wrong with the base K2. I still have to do what Don suggested about connection to an external watt meter.
> >>>
> > ______________________________________________________________
> > 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
> >
>

ny4g

Re: K2: High SWR On Dummy Load

In reply to this post by Don Wilhelm-4

Don,

I took off the shield on the KPA100 and those two diodes are tight against the back panel and the toroid. What would you recommend is the best way to desolder and replace those? It is tight against the back panel and a toroid. I do not want to risk damaging the nearby toroid - so I think I will remove the the standoffs and remove the PCB from the heat sink and desolder it from the back side (non component) side. Is this what you would do?

Thanks

Ariel NY4G

Sent from my iPad

On Oct 26, 2012, at 8:10 AM, "Don Wilhelm" <[hidden email]> wrote:

> Ariel,
>
> You may indeed have a problem with D9 and the 3 associated resistors in the base K2, BUT when the KAT2 or the KPA100 is installed, that circuit is ignored.
> Both the KAT2 and the KPA100 contain a true wattmeter that is positioned right at the output and used for power control.
>
> The K2 microprocessor reads the actual output and compares that to the power knob setting. That result tells the microprocessor how to adjust the drive. Unlike other ham transceivers, the K2 uses a closed loop to control the power instead of simply adjusting the drive.
>
> What that also means is that the wattmeter in the KPA100 is not working (you have shown that the one in the KAT2 is working OK). As I indicated before (and also indicated by your high SWR indication) there is a high probability that KPA100 diodes D16 and D17 have been damaged.
>
> When the diodes are damaged, the output back to the MCU is most likely zero, and the MCU *thinks* there is no power output - it then increases the drive to the maximum in an attempt to develop power. The result is a HiCur warning and stress on the base K2 PA transistors.
>
> Replace KPA100 D16 and D17 as the first order of business and after that you can investigate any remaining problems. Note that those diodes can be "half bad" and may show as good with a diode test - replacement is the first order of business.
>
> 73,
> Don W3FPR
>
> On 10/25/2012 11:31 PM, Ariel Jacala wrote:
>> Don
>>
>> The K2 with the ATU behaves as expected - internal meter agrees well with the external meter, current draw is as expected, and so forth for various power levels up to 10watts checked out. It was connected to a dummy load.
>>
>> Without the ATU and the dummy load connected to the base K2 antenna, things are rather strange.... At 2 watts set on the power knob, output on the external meter is 2.7 watts and current draw is 0.96 amps; at a knob setting of 2.4 watts, output is up to 7 watts on the external meter and current draw is 1.4 amps; at a knob setting of 2.5 watts, power output is 10 watts and current draw is 1.96 amps; at 3 watts knob setting, I get the high current warning, and the external meter is pegged.
>>
>> This leads me to believe that the base K2 is overdriving the KPA100. At low power settings - 5 watts, I was pegging the LEDs indicating power on the LDG100 autotuner, at over 125 watts.
>>
>> Ariel NY4G
>>
>> Sent from my iPad
>>
>> On Oct 25, 2012, at 11:51 AM, "Don Wilhelm" <[hidden email]> wrote:
>>
>>> Ariel,
>>>
>>> Do not be too quick to conclude that there is something wrong with the base K2. The basic K2 uses only an RF voltage diode to display the power output, and it may not be exact - it depends on the load and may vary from band to band - if it only off by a watt or two, then all is OK That is bypassed when the KAT2 or KPA100 is installed.
>>>
>>> Yes, do check with the external wattmeter - both with and without the KPA100. I still think KPA100 diodes D16 and D17 are highest on the suspect list with other KPA100 wattmeter components being second on that list.
>>>
>>> 73,
>>> Don W3FPR
>>>
>>> On 10/25/2012 11:18 AM, Ariel Jacala wrote:
>>>> Thanks to Jim, Vic and Don for the return comments
>>>>
>>>> I disconnected the KPA100 and put on the K2 top with the KAT2 ATU. With the K2 ATU connected and the dummy load connected - the SWR correctly reads 1:1 with menu set for CALS. With the menu set to CALP, the power levels appeared to modulate correctly with the PWR knob although this is an item i have to double check. With the ATU disconnected, the displayed power on tune differs from the power setting. This suggests to me that there is something wrong with the base K2. I still have to do what Don suggested about connection to an external watt meter.
>>>>
>> ______________________________________________________________
>> 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
>>
>

Don Wilhelm-4

Re: K2: High SWR On Dummy Load

Ariel.

While it is sometimes possible to clip the leads on the top of the board
and use the remaining leads to mount new diodes, I suggest that "is
cheating". I always remove the board from the heatsink and de-solder
the diodes from below.
Usually, the thermal pads will stay in place and can be re-used unless
they become torn.

73,
Don W3FPR
On 10/31/2012 10:34 PM, Ariel Jacala wrote:
> Don,
>
> I took off the shield on the KPA100 and those two diodes are tight against the back panel and the toroid. What would you recommend is the best way to desolder and replace those? It is tight against the back panel and a toroid. I do not want to risk damaging the nearby toroid - so I think I will remove the the standoffs and remove the PCB from the heat sink and desolder it from the back side (non component) side. Is this what you would do?
>

______________________________________________________________
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Post: mailto:[hidden email]

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ny4g

Re: K2: High SWR On Dummy Load

Don and all who helped

Diodes have been replaced. Everything is back to normal

Thanks

Ariel NY4G

Sent from my iPad

On Oct 31, 2012, at 11:02 PM, "Don Wilhelm" <[hidden email]> wrote:

> Ariel.
>
> While it is sometimes possible to clip the leads on the top of the board and use the remaining leads to mount new diodes, I suggest that "is cheating". I always remove the board from the heatsink and de-solder the diodes from below.
> Usually, the thermal pads will stay in place and can be re-used unless they become torn.
>
> 73,
> Don W3FPR
> On 10/31/2012 10:34 PM, Ariel Jacala wrote:
>> Don,
>>
>> I took off the shield on the KPA100 and those two diodes are tight against the back panel and the toroid. What would you recommend is the best way to desolder and replace those? It is tight against the back panel and a toroid. I do not want to risk damaging the nearby toroid - so I think I will remove the the standoffs and remove the PCB from the heat sink and desolder it from the back side (non component) side. Is this what you would do?
>>
>