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KPA100 Upgrade and KAT100 Problem

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John Huffman-2

KPA100 Upgrade and KAT100 Problem

I had been having problems with my KAT100 and hoped the KPA100 upgrade
would help. I installed the upgrade and all works well with an external
tuner other than the KAT100. But, the KAT100 problems persist.

Here's the problem. The KAT100 tunes fine on all bands into my 50 ohm
dummy load if I set the power to 10 watts. But, if I set it to 11
watts, engaging the KPA100 build into my K2, the bands 160m through 40m
won't tune correctly.

On 160m I get just one LED lighting at a time and the relays search for
a match. The resulting match is 9.9:1.

On 80m no LEDs light as the relays click searching for a match. The
resulting match is 9.9:1

On 40m one LED lights as it searches for a match. The resulting match
is 1.4:1. But, when operating full power, only one LED lights at a time
and the LED that's lit changes every second or less.

On 30m and above the KAT100 tunes fine but the match can be as much as
1.4:1, though most are 1:1.

When operating full power, all LEDs light with each key stroke. On some
bands all but the last 2 or 3 light when you are keying. In QRP mode
about half light when you are keying. There is no high SWR warning.
There seems to be some power reduction at full power.

Again, all of the things above are into a 50 ohm dummy load. Using a
real antenna I get the same problems.

These symptoms are not always consistent, but there is always a problem.

Sometimes when tuning on one of the lower bands, especially 40m, if the
tuner had a tough time tuning, the KDSP2 will report that it is not
installed. Turning the K2 off and then on restores the KDSP2.

Individual component testing at 10m, 20 watts
L0 - L8 SWR = 9.9:1
C0 = 4:1
C1 = 3:1
C2 = starts at 4:1 climbs to 6:1
C3 = 8:1
C4,C5,C6,C7,n1,n2 = 9.9:1

Individual component testing at 40m, 20 watts
All components show 9.9:1

Suggestions on where to start greatly appreciated.

73 de K1ESE
John

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Don Wilhelm-3

RE: KPA100 Upgrade and KAT100 Problem

John,

I believe the problem is entirely in your KAT100.

Check all your connecting cables first thing (do a continuity test on both
the center conductor and shield and check for shorts). It sounds like your
tuner is operating into an open circuit or a shorted one.

If you have an antenna analyzer, check each cable with it while connected at
the far end to a dummy load.

After checking the cables, if you still have problems, try re-calibrating
the wattmeter in the KAT100. Also check the soldering in the KAT100 control
and wattmeter sections - particularly RP1 and the pins of U3. In fact check
all the soldering in the KAT100.

Pins 6 and 7 of U3 must go to a low level (to scale the wattmeter readings)
when high power is active. Check to be certain that is happening and that
the low level scaling signals are getting to pins 2 and 4 of RP1.

73,
Don W3FPR

> -----Original Message-----
>
>
> I had been having problems with my KAT100 and hoped the KPA100 upgrade
> would help. I installed the upgrade and all works well with an external
> tuner other than the KAT100. But, the KAT100 problems persist.
>
> Here's the problem. The KAT100 tunes fine on all bands into my 50 ohm
> dummy load if I set the power to 10 watts. But, if I set it to 11
> watts, engaging the KPA100 build into my K2, the bands 160m through 40m
> won't tune correctly.
>
>

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John Huffman-2

Re: KPA100 Upgrade and KAT100 Problem

Don -

Thanks for the guidance.

> Check all your connecting cables first thing (do a continuity test on both
> the center conductor and shield and check for shorts).
OK

> If you have an antenna analyzer, check each cable with it while connected at
> the far end to a dummy load.
OK

> After checking the cables, if you still have problems, try re-calibrating
> the wattmeter in the KAT100.
Did that and the setting, especially forward was off by quite a bit.

> Pins 6 and 7 of U3 must go to a low level (to scale the wattmeter readings)
> when high power is active.
The Logic selection on my DMM shows LO between ground and pins 6 and 7
of U3 at all times, both high and low power.

Tried again and the KAT100 works a bit better, but the higher the power,
more LEDs light. On 80m at 20W the K2 shows 1.1:1 SWR, but the KAT100
LEDs show 1.3:1. Transmit at full power and all LEDs light and the K2
locks in transmit mode requiring tapping the key several times to get
back to receive.

On 80m at 2w with KAT100 set to AUTO, all is well. With KAT100 set to
CAL, all LEDs light when the key is tapped.

I will do some soldering remelts. Have had problems in the past with
Q3, which was replaced.

Do these symptoms lead to other conclusions?

As always, many thanks, Don.

73 de K1ESE
John

Check to be certain that is happening and that

> the low level scaling signals are getting to pins 2 and 4 of RP1.
>
> 73,
> Don W3FPR
>
>> -----Original Message-----
>>
>>
>> I had been having problems with my KAT100 and hoped the KPA100 upgrade
>> would help. I installed the upgrade and all works well with an external
>> tuner other than the KAT100. But, the KAT100 problems persist.
>>
>> Here's the problem. The KAT100 tunes fine on all bands into my 50 ohm
>> dummy load if I set the power to 10 watts. But, if I set it to 11
>> watts, engaging the KPA100 build into my K2, the bands 160m through 40m
>> won't tune correctly.
>>
>>
>
>

Don Wilhelm-3

RE: KPA100 Upgrade and KAT100 Problem

John,

Let's try that measurement of U3 pins 6 and 7 again, this time with the
KAT100 in CAL mode and after pressing TUNE. Those pins should read zero
volts during transmit when th epower is set for 11 watts or more, but should
go to a higher voltage if the power is less than 10 watts.

If that is not happening, then your wattmeter is not being scaled for both
high and low power, and if the SWR is anything other than a true 1:1, the
number of LEDs lit on the tuner will increase as the power is increased.

73,
Don W3FPR

> -----Original Message-----
> > Pins 6 and 7 of U3 must go to a low level (to scale the
> wattmeter readings)
> > when high power is active.
> The Logic selection on my DMM shows LO between ground and pins 6 and 7
> of U3 at all times, both high and low power.
>

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John Huffman-2

Re: KPA100 Upgrade and KAT100 Problem

In reply to this post by Don Wilhelm-3

Don -

I have gone from bad to worse. I remelted some solder joints, replaced
the 1n5711 diodes, and re-calibrated the tuner. It seemed to work for a
bit, but problems returned. But now the K2/100 also has problems.

With the KAT100 I tuned the antenna to 80m. It worked OK on QRP, but
with the KPA100 engaged the amp shows high reflected and locks on transmit.

I removed the KAT100 and used a manual tuner. Tunes fine at QRP, but
with the KPA100 on, it is like the K2/100 is on a different frequency.
The tuner setting that was fine in QRP now has high SWR. When I go from
20w to full power, the K2 locks in transmit at full power out. I have
to power it off to quit transmitting.

This same set-up, manual tuner, and antenna have worked fine since it
was setup weeks ago.

With a dummy load on the K2/100 all works well. Tried other cables and
yet another tuner with no success. The K2/100 locks up.

Could I have blown diodes in the KPA100 SWR bridge?

Status - KAT100 has wild LEDs and doesn't like high power.
KPA100 doesn't like 80m and locks in transmit.

73 de K1ESE
John

Don Wilhelm wrote:

> John,
>
> I believe the problem is entirely in your KAT100.
>
> Check all your connecting cables first thing (do a continuity test on both
> the center conductor and shield and check for shorts). It sounds like your
> tuner is operating into an open circuit or a shorted one.
>
> If you have an antenna analyzer, check each cable with it while connected at
> the far end to a dummy load.
>
> After checking the cables, if you still have problems, try re-calibrating
> the wattmeter in the KAT100. Also check the soldering in the KAT100 control
> and wattmeter sections - particularly RP1 and the pins of U3. In fact check
> all the soldering in the KAT100.
>
> Pins 6 and 7 of U3 must go to a low level (to scale the wattmeter readings)
> when high power is active. Check to be certain that is happening and that
> the low level scaling signals are getting to pins 2 and 4 of RP1.
>
> 73,
> Don W3FPR
>
>> -----Original Message-----
>>
>>
>> I had been having problems with my KAT100 and hoped the KPA100 upgrade
>> would help. I installed the upgrade and all works well with an external
>> tuner other than the KAT100. But, the KAT100 problems persist.
>>
>> Here's the problem. The KAT100 tunes fine on all bands into my 50 ohm
>> dummy load if I set the power to 10 watts. But, if I set it to 11
>> watts, engaging the KPA100 build into my K2, the bands 160m through 40m
>> won't tune correctly.
>>
>>
>
>

Don Wilhelm-3

RE: KPA100 Upgrade and KAT100 Problem

John,

It sounds like your KPA100 is self oscillating when on 80 meters (and
perhaps other bands too).
That fact alone will drive your KAT100 crazy.
An oscillation problem will not show up on a dummy load because the dummy
load is not frequency sensitive (an antenna and tuner will be frequency
sensitive).

Check your work on the KPA100 upgrade. I know that if Q6 and Q7 are not
working properly, the KPA100 can turn into a big oscillator. Check the DC
Voltages of Q6 and Q7 against the DC Voltage chart in the new KPA100 manual
(download it from the Elecraft website - the one in your older manual is not
correct after the upgrade).

Leave the KAT100 situation rest until you have the KPA100 working properly.
You might want to use only your manual tuner while testing the KPA100.

The KPA100 locking up sounds like an RF feedback problem, and if present,
that can complicate your observations.

73,
Don W3FPR

> -----Original Message-----
>
> Don -
>
> I have gone from bad to worse. I remelted some solder joints, replaced
> the 1n5711 diodes, and re-calibrated the tuner. It seemed to work for a
> bit, but problems returned. But now the K2/100 also has problems.
>
> With the KAT100 I tuned the antenna to 80m. It worked OK on QRP, but
> with the KPA100 engaged the amp shows high reflected and locks on
> transmit.
>
> I removed the KAT100 and used a manual tuner. Tunes fine at QRP, but
> with the KPA100 on, it is like the K2/100 is on a different frequency.
> The tuner setting that was fine in QRP now has high SWR. When I go from
> 20w to full power, the K2 locks in transmit at full power out. I have
> to power it off to quit transmitting.
>
> This same set-up, manual tuner, and antenna have worked fine since it
> was setup weeks ago.
>
> With a dummy load on the K2/100 all works well. Tried other cables and
> yet another tuner with no success. The K2/100 locks up.
>

John Huffman-2

Re: KPA100 Upgrade and KAT100 Problem

Don -

Yes, let's settle the KPA100 first as that's the latest changes I have
made by doing the upgrade kit.

Q6 has the correct voltages except for the drain on transmit. Manual
says 115v and I get 135v. Voltages on Q7 look the same as in the
manual. I measured R11 which feeds the Q6 drain and it is 495 ohms,
just a bit lower than the 510 ohms in the manual.

I then measured the voltage input and Q6 sides of R11. In receive the
voltage input is 128v and the Q6 side is .6v and in transmit the voltage
input is 142v and the Q6 side is 135v.

Looks like too much voltage on Q6 but not sure where to go from here.
The only change I made in this part of the board was to replace R4 with
a 100k in the upgrade kit.

73 de K1ESE
John

Don Wilhelm wrote:

> John,
>
> It sounds like your KPA100 is self oscillating when on 80 meters (and
> perhaps other bands too).
> That fact alone will drive your KAT100 crazy.
> An oscillation problem will not show up on a dummy load because the dummy
> load is not frequency sensitive (an antenna and tuner will be frequency
> sensitive).
>
> Check your work on the KPA100 upgrade. I know that if Q6 and Q7 are not
> working properly, the KPA100 can turn into a big oscillator. Check the DC
> Voltages of Q6 and Q7 against the DC Voltage chart in the new KPA100 manual
> (download it from the Elecraft website - the one in your older manual is not
> correct after the upgrade).
>
> Leave the KAT100 situation rest until you have the KPA100 working properly.
> You might want to use only your manual tuner while testing the KPA100.
>
> The KPA100 locking up sounds like an RF feedback problem, and if present,
> that can complicate your observations.
>
> 73,
> Don W3FPR
>
>> -----Original Message-----
>>
>> Don -
>>
>> I have gone from bad to worse. I remelted some solder joints, replaced
>> the 1n5711 diodes, and re-calibrated the tuner. It seemed to work for a
>> bit, but problems returned. But now the K2/100 also has problems.
>>
>> With the KAT100 I tuned the antenna to 80m. It worked OK on QRP, but
>> with the KPA100 engaged the amp shows high reflected and locks on
>> transmit.
>>
>> I removed the KAT100 and used a manual tuner. Tunes fine at QRP, but
>> with the KPA100 on, it is like the K2/100 is on a different frequency.
>> The tuner setting that was fine in QRP now has high SWR. When I go from
>> 20w to full power, the K2 locks in transmit at full power out. I have
>> to power it off to quit transmitting.
>>
>> This same set-up, manual tuner, and antenna have worked fine since it
>> was setup weeks ago.
>>
>> With a dummy load on the K2/100 all works well. Tried other cables and
>> yet another tuner with no success. The K2/100 locks up.
>>
>
>