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[K2} K2-100 Test and Alignment Issues

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William Moore-5

[K2} K2-100 Test and Alignment Issues

I am now into the test and alignment phases of my just constructed KPA-100
amplifier to be integrated into K2 #3842. Right from the start of this
phase, I have run headlong into a two issues I just can't figure out.

I am constructing from the Revision G September 2010 manual. On the page 47,
the voltage test chart, all measurements are in accordance with the ranges
in the chart except for J3+ lead where instead of 0 volts, I am reading a
stable and consistent 0.044 volts; certainly not a significant voltage but
none the less, it is not zero as called for in the chart.

The second issue is with reference to the C1 SWR Bridge Null Adjustment
described on page 48. Adjusting C1 varies the power output reading on the K2
LCD but does not vary the SWR readout which remains at 9.9 to 1. However,
the SWR/watt meter on my Kenwood AT-200 antenna tuner indicates the K2 is
running 15 watts with an SWR of 1 to 1 into the dummy load, a Heathkit
Cantenna. Twisting the power pot has no effect on the actual power output as
measured on the Kenwood AT-200. Removing the all connections between the K2
and the KPA-100, the K2 functions normally with the power setting pot.

I would really appreciate hearing from anyone who can offer any clues to
what I am doing wrong in conducting these measurements and adjustments or
perhaps identifying a possible construction mistake but gee, I checked so
carefully.

Thank you,

Bill, VE2WMA

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Don Wilhelm-4

Re: [K2} K2-100 Test and Alignment Issues

Bill,

For the J3+ lead, I think the PA transistors may be producing that
voltage in response to light shining on them. Shield the transistors
from light and see if the voltage changes - if so, ignore it.

As for the C1 adjustment - do the following steps in order. Preset R26
and R27 to about mid-range. If you want a closer setting, measure the
resistance to ground from the center pin on the pot and set it close to
43k - you can measure from U5 pin 3 and pin 5 for easier access than the
actual potentiometer.

Balance the wattmeter by adjusting C1 - monitor the voltage at TP4 while
sending 40 meter power through the wattmeter. You should be able to
obtain a very near zero voltage if all is well. If you cannot obtain a
very low voltage, there is a problem with one or more of the following:
T4, D16, D17, R28, R29, C95 or C1.
Check the windings of T4 first to be certain the correct leads are in
the right holes and have been well stripped and tinned (if there is any
question, rewind T4 with new wire). Then check the orientation of D16
and D17 against the parts placement diagram at the back of the manual.
Be certain all the parts I mentioned are well soldered and there are no
solder bridges.
T4 does have a 3rd winding, and that is the red wire from the center of
the SO-239 jack to the board for T4-6 and the bare wire from the center
of the SO-239 to the board hole marked T4-5. Be certain the bare wire
is not touching the shell of the SO-239 and was trimmed so it is not
grounding against the heatsink.

Once you have achieved the balance point for C1, do not change its position.
Adjust R26 during a TUNE to indicate the same power on the K2 display as
you read on your external wattmeter.
Then adjust R27 to the same position as R26 unless you have a load which
can produce a known SWR below 2.0:1, in which case you can use that load
and adjust R27 until the K2 shows that known SWR.

You can initially set R26 and R27 with the low power from the base K2
(do not connect the APP power cable). Later you may want to refine the
R26 setting using 80 or 100 watts.

Let us know how you make out.

73,
Don W3FPR

On 1/27/2014 2:02 PM, William Moore wrote:

> I am now into the test and alignment phases of my just constructed KPA-100
> amplifier to be integrated into K2 #3842. Right from the start of this
> phase, I have run headlong into a two issues I just can't figure out.
>
> I am constructing from the Revision G September 2010 manual. On the page 47,
> the voltage test chart, all measurements are in accordance with the ranges
> in the chart except for J3+ lead where instead of 0 volts, I am reading a
> stable and consistent 0.044 volts; certainly not a significant voltage but
> none the less, it is not zero as called for in the chart.
>
> The second issue is with reference to the C1 SWR Bridge Null Adjustment
> described on page 48. Adjusting C1 varies the power output reading on the K2
> LCD but does not vary the SWR readout which remains at 9.9 to 1. However,
> the SWR/watt meter on my Kenwood AT-200 antenna tuner indicates the K2 is
> running 15 watts with an SWR of 1 to 1 into the dummy load, a Heathkit
> Cantenna. Twisting the power pot has no effect on the actual power output as
> measured on the Kenwood AT-200. Removing the all connections between the K2
> and the KPA-100, the K2 functions normally with the power setting pot.
>
> I would really appreciate hearing from anyone who can offer any clues to
> what I am doing wrong in conducting these measurements and adjustments or
> perhaps identifying a possible construction mistake but gee, I checked so
> carefully.
>
>

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Don Wilhelm-4

Re: [K2} K2-100 Test and Alignment Issues

In reply to this post by William Moore-5

By the way - adjust C1 with a non-metallic screwdriver. Both sides of
C1 are above ground.

73,
Don W3FPR
------------------------------------------------
Bill,

For the J3+ lead, I think the PA transistors may be producing that
voltage in response to light shining on them. Shield the transistors
from light and see if the voltage changes - if so, ignore it.

As for the C1 adjustment - do the following steps in order. Preset R26
and R27 to about mid-range. If you want a closer setting, measure the
resistance to ground from the center pin on the pot and set it close to
43k - you can measure from U5 pin 3 and pin 5 for easier access than the
actual potentiometer.

Balance the wattmeter by adjusting C1 - monitor the voltage at TP4 while
sending 40 meter power through the wattmeter. You should be able to
obtain a very near zero voltage if all is well. If you cannot obtain a
very low voltage, there is a problem with one or more of the following:
T4, D16, D17, R28, R29, C95 or C1.
Check the windings of T4 first to be certain the correct leads are in
the right holes and have been well stripped and tinned (if there is any
question, rewind T4 with new wire). Then check the orientation of D16
and D17 against the parts placement diagram at the back of the manual.
Be certain all the parts I mentioned are well soldered and there are no
solder bridges.
T4 does have a 3rd winding, and that is the red wire from the center of
the SO-239 jack to the board for T4-6 and the bare wire from the center
of the SO-239 to the board hole marked T4-5. Be certain the bare wire
is not touching the shell of the SO-239 and was trimmed so it is not
grounding against the heatsink.

Once you have achieved the balance point for C1, do not change its position.
Adjust R26 during a TUNE to indicate the same power on the K2 display as
you read on your external wattmeter.
Then adjust R27 to the same position as R26 unless you have a load which
can produce a known SWR below 2.0:1, in which case you can use that load
and adjust R27 until the K2 shows that known SWR.

You can initially set R26 and R27 with the low power from the base K2
(do not connect the APP power cable). Later you may want to refine the
R26 setting using 80 or 100 watts.

Let us know how you make out.

73,
Don W3FPR

On 1/27/2014 2:02 PM, William Moore wrote:

John Oglesby-2

Re: [K2} K2-100 Test and Alignment Issues

In reply to this post by William Moore-5

Bill - I had this exact problem on my K2/100 during testing. Changing
C1 varied the power output, but the SWR was fixed at 9.9-1. The problem
was a short between the output of the two op-amps U5A and U5B that
amplify and buffer the forward and reflected voltages before they go to
the processor. There are two resistors on the outputs that are very
close to each other and the pads were shorted so the processor saw the
same voltage for forward and reflected - ergo SWR of 9.9-1. And the
voltage varied with the C1 setting as the bridge went in and out of
balance - ergo the varying power indication. Totally a build error.
When I folded over the resistor leads, they ended up looking like they
were on a single pad. I think if you look at that area you will find
the problem.

Good Luck.

73
John
N9RE
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Don Wilhelm-4

Re: [K2} K2-100 Test and Alignment Issues

As John has pointed out, the problem can be anywhere in the KPA100
wattmeter circuit consisting of T4, C1, C95. R28, R29, D16, D17, R26,
R27, U5. R24. R25, Q10, Q11, and U6. With a bit more information and
some measurements that I can suggest, the field of suspect components
(and soldering thereof) can be reduced substantially.

73,
Don W3FPR

On 1/28/2014 3:31 PM, John Oglesby wrote:

> Bill - I had this exact problem on my K2/100 during testing. Changing
> C1 varied the power output, but the SWR was fixed at 9.9-1. The
> problem was a short between the output of the two op-amps U5A and U5B
> that amplify and buffer the forward and reflected voltages before they
> go to the processor. There are two resistors on the outputs that are
> very close to each other and the pads were shorted so the processor
> saw the same voltage for forward and reflected - ergo SWR of 9.9-1.
> And the voltage varied with the C1 setting as the bridge went in and
> out of balance - ergo the varying power indication. Totally a build
> error. When I folded over the resistor leads, they ended up looking
> like they were on a single pad. I think if you look at that area you
> will find the problem.
>

William Moore-5

Re: [K2] K2-100 Test and Alignment Issues

In reply to this post by Don Wilhelm-4

Don and John,

Thank you so much for coming to my aid with these baffling (to me) problems.
I have undertaken both your suggestions but still, unfortunately, no joy.

The J3+ issue The J3+ lead now gives a voltage reading of -0.225 volts while
covering the PA transistors with a thick cardboard and a mostly darkened
room. I can also confirm, absolutely, that no 13.8 volt current has ever
passed through J3 or the Aux 12 volt line to the K2.

The Wattmeter issue. I reset R26 and 27 to 43K and tried once again to
balance the wattmeter with C1. Twisting C1 with a plastic handled screw
driver, I got the voltage at Test Point 4 down to 1.4 volts but I am not
sure if that is what you mean by "close to 0.0 volts". At the same time,
glancing at the K2 LCD it still shows a 9.9::1 swr and the watt meter on my
Kenwood AT-200 antenna tuner bypassed to a dummy load indicates the K2 is
pumping out a full 15 watts. Varying C1 while looking only at the K2 LCD, I
can get 1.0::1 SWR but the power out on the LCD registers 0.1 watts while
the AT-200 wattmeter says the K2 is still pushing 15 watts to the dummy
load. Varying C1 does not change the 15 watt output on the KAT200 watt
metre. It always remains at a constant 15 watts.

I then disassembled the KPA-100 circuit board from the heatsink. I checked
that all the components you listed were the correct values and oriented
properly i.e., D16 and D17. I checked the solder joints until my eyes
crossed with a lamp having a magnifying lens in the centre of the
fluorescent bulb. I found no solder bridges, unsoldered leads or poorly
soldered solder pads. I thinks John's problem that he referred to in his
post was a solder bridge between R24 and R26 but I found this junction was
clean of any hint of a solder bridge. I found no protruding grounding leads
anywhere. I am quite sure but, not absolutely sure, that T4 is wound (12
turns twisted wire counted inside the core), wired and soldered correctly
with no leads shorting. The T4 solder pads are full with bright silvery
solder, no craters and the solder flows through the holes to the top of the
circuit board.

The only variable that I can see left is to pull T4, rewind and reinstall.
However, before I do this, is there any other measurements, checks or
procedures that I have overlooked or new ones that can be suggested?

My career background is in the field of business and economics so I kind of
feel like I am an auto mechanic trying to diagnose and perform surgery on a
complex cardiology problem. That is to say, I really appreciate your help.

73

Bill, VE2WMA

-----Original Message-----
From: Don Wilhelm [mailto:[hidden email]]
Sent: Monday, January 27, 2014 2:58 PM
To: William Moore; [hidden email]
Subject: Re: [Elecraft] [K2} K2-100 Test and Alignment Issues

Bill,

For the J3+ lead, I think the PA transistors may be producing that voltage
in response to light shining on them. Shield the transistors from light and
see if the voltage changes - if so, ignore it.

As for the C1 adjustment - do the following steps in order. Preset R26 and
R27 to about mid-range. If you want a closer setting, measure the
resistance to ground from the center pin on the pot and set it close to 43k
- you can measure from U5 pin 3 and pin 5 for easier access than the actual
potentiometer.

Balance the wattmeter by adjusting C1 - monitor the voltage at TP4 while
sending 40 meter power through the wattmeter. You should be able to obtain
a very near zero voltage if all is well. If you cannot obtain a very low
voltage, there is a problem with one or more of the following:
T4, D16, D17, R28, R29, C95 or C1.
Check the windings of T4 first to be certain the correct leads are in the
right holes and have been well stripped and tinned (if there is any
question, rewind T4 with new wire). Then check the orientation of D16 and
D17 against the parts placement diagram at the back of the manual.
Be certain all the parts I mentioned are well soldered and there are no
solder bridges.
T4 does have a 3rd winding, and that is the red wire from the center of the
SO-239 jack to the board for T4-6 and the bare wire from the center of the
SO-239 to the board hole marked T4-5. Be certain the bare wire is not
touching the shell of the SO-239 and was trimmed so it is not grounding
against the heatsink.

Once you have achieved the balance point for C1, do not change its position.
Adjust R26 during a TUNE to indicate the same power on the K2 display as you
read on your external wattmeter.
Then adjust R27 to the same position as R26 unless you have a load which can
produce a known SWR below 2.0:1, in which case you can use that load and
adjust R27 until the K2 shows that known SWR.

You can initially set R26 and R27 with the low power from the base K2 (do
not connect the APP power cable). Later you may want to refine the
R26 setting using 80 or 100 watts.

Let us know how you make out.

73,
Don W3FPR

On 1/27/2014 2:02 PM, William Moore wrote:
> I am now into the test and alignment phases of my just constructed
> KPA-100 amplifier to be integrated into K2 #3842. Right from the start
> of this phase, I have run headlong into a two issues I just can't figure
out.
>
> I am constructing from the Revision G September 2010 manual. On the
> page 47, the voltage test chart, all measurements are in accordance
> with the ranges in the chart except for J3+ lead where instead of 0
> volts, I am reading a stable and consistent 0.044 volts; certainly not
> a significant voltage but none the less, it is not zero as called for in
the chart.
>
> The second issue is with reference to the C1 SWR Bridge Null
> Adjustment described on page 48. Adjusting C1 varies the power output
> reading on the K2 LCD but does not vary the SWR readout.......

______________________________________________________________
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Help: http://mailman.qth.net/mmfaq.htm
Post: mailto:[hidden email]

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Don Wilhelm-4

Re: [K2] K2-100 Test and Alignment Issues

Bill,

Regarding T4, there is one other possibility that I did not mention
before. If the direction of the windings is not as shown in the manual,
it will work "backwards" which may be what you are observing.

As for the minimum voltage of 1.4 volts, that is WAY too high. The
bridge should null to less than 14 millivolts with 15 or 20 watts
flowing through it.

You could do a sanity check on it by attempting to null the bridge by
monitoring the DC voltage at U5 pin 3 rather than U5 pin 1. The voltage
on U5 pin 1 should be the same as at pin 3 if U5 is working OK.
If you still have a high voltage at U5 pin 3, then try doing the balance
(nulling) while monitoring U5 pin 5. If you can obtain a null at U5 pin
5, then for certain T4 is wound in the wrong direction.

73,
Don W3FPR

On 1/30/2014 4:39 PM, William Moore wrote:

> Don and John,
>
> Thank you so much for coming to my aid with these baffling (to me) problems.
> I have undertaken both your suggestions but still, unfortunately, no joy.
>
> The J3+ issue The J3+ lead now gives a voltage reading of -0.225 volts while
> covering the PA transistors with a thick cardboard and a mostly darkened
> room. I can also confirm, absolutely, that no 13.8 volt current has ever
> passed through J3 or the Aux 12 volt line to the K2.
>
> The Wattmeter issue. I reset R26 and 27 to 43K and tried once again to
> balance the wattmeter with C1. Twisting C1 with a plastic handled screw
> driver, I got the voltage at Test Point 4 down to 1.4 volts but I am not
> sure if that is what you mean by "close to 0.0 volts". At the same time,
> glancing at the K2 LCD it still shows a 9.9::1 swr and the watt meter on my
> Kenwood AT-200 antenna tuner bypassed to a dummy load indicates the K2 is
> pumping out a full 15 watts. Varying C1 while looking only at the K2 LCD, I
> can get 1.0::1 SWR but the power out on the LCD registers 0.1 watts while
> the AT-200 wattmeter says the K2 is still pushing 15 watts to the dummy
> load. Varying C1 does not change the 15 watt output on the KAT200 watt
> metre. It always remains at a constant 15 watts.
>
> I then disassembled the KPA-100 circuit board from the heatsink. I checked
> that all the components you listed were the correct values and oriented
> properly i.e., D16 and D17. I checked the solder joints until my eyes
> crossed with a lamp having a magnifying lens in the centre of the
> fluorescent bulb. I found no solder bridges, unsoldered leads or poorly
> soldered solder pads. I thinks John's problem that he referred to in his
> post was a solder bridge between R24 and R26 but I found this junction was
> clean of any hint of a solder bridge. I found no protruding grounding leads
> anywhere. I am quite sure but, not absolutely sure, that T4 is wound (12
> turns twisted wire counted inside the core), wired and soldered correctly
> with no leads shorting. The T4 solder pads are full with bright silvery
> solder, no craters and the solder flows through the holes to the top of the
> circuit board.
>
> The only variable that I can see left is to pull T4, rewind and reinstall.
> However, before I do this, is there any other measurements, checks or
> procedures that I have overlooked or new ones that can be suggested?
>
> My career background is in the field of business and economics so I kind of
> feel like I am an auto mechanic trying to diagnose and perform surgery on a
> complex cardiology problem. That is to say, I really appreciate your help.
>
>

William Moore-5

Re: [K2] K2-100 Test and Alignment Issues

Don,

Thanks you for this tip, and yes, I now realize my windings on T4 are not
exactly as shown in the manual. However this realization raises a broader
concern.

Here is what happened. I wound my toriods using a winding tip I'm sure I
picked up on the Elecraft list some time ago. To wind the toriods, I put the
wire(s) to be wound on the core through the toroid core half way, pull up
the two ends at a 12 o'clock point on the toroid core then wind one lead
counter clockwise to about 7 o'clock and the other lead clockwise to about 5
o'clock. I now realize that this will result in the toroid being would in
reverse to probably the standard winding practice of starting only one long
lead at 7 o'clock on the toroid core and then winding all the required turns
on the core around to about 5 o'clock.

I have now pulled, T4 and rewound it exactly as shown in the manual. I am
ready to reinstall it but before I do, here is the broader concern. I have
also reverse wound T3 as well as each and every other toroid core on the
KPA-100! Do you think this will create problems such that I will have to
remove, rewind and reinstall all the toriods, just certain toriods or is it
just T4 that is an issue? What makes me wonder is that I built my entire K2
and the KBS2 using the "12 o'clock high two-lead core winding system" and
the K2 works just fine for me but then I can't verify if the my K2 is really
performing exactly to specifications because I don't have test facilities to
do so.

I would really appreciate your comments on this issue before reassembling
the circuit board back onto the heatsink in case I need to make other
changes to the toriods.

Thank you.

Bill, VE2WMA

-----Original Message-----
From: Don Wilhelm [mailto:[hidden email]]
Sent: Thursday, January 30, 2014 4:50 PM
To: William Moore; [hidden email]; [hidden email]; 'Mike Harris'
Subject: Re: [Elecraft] [K2] K2-100 Test and Alignment Issues

Bill,

Regarding T4, there is one other possibility that I did not mention before.
If the direction of the windings is not as shown in the manual, it will work
"backwards" which may be what you are observing.

As for the minimum voltage of 1.4 volts, that is WAY too high. The bridge
should null to less than 14 millivolts with 15 or 20 watts flowing through
it.

You could do a sanity check on it by attempting to null the bridge by
monitoring the DC voltage at U5 pin 3 rather than U5 pin 1. The voltage on
U5 pin 1 should be the same as at pin 3 if U5 is working OK.
If you still have a high voltage at U5 pin 3, then try doing the balance
(nulling) while monitoring U5 pin 5. If you can obtain a null at U5 pin 5,
then for certain T4 is wound in the wrong direction.

73,
Don W3FPR

On 1/30/2014 4:39 PM, William Moore wrote:
> Don and John,
>
> Thank you so much for coming to my aid with these baffling (to me)
problems.
> I have undertaken both your suggestions but still, unfortunately, no joy.
>
> The J3+ issue The J3+ lead now gives a voltage reading of -0.225 volts
while
> covering the PA transistors with a thick cardboard and a mostly darkened
> room. I can also confirm, absolutely, that no 13.8 volt current has ever
> passed through J3 or the Aux 12 volt line to the K2.
>
> The Wattmeter issue. I reset R26 and 27 to 43K and tried once again to
> balance the wattmeter with C1. Twisting C1 with a plastic handled screw
> driver, I got the voltage at Test Point 4 down to 1.4 volts but I am not
> sure if that is what you mean by "close to 0.0 volts". At the same time,
> glancing at the K2 LCD it still shows a 9.9::1 swr and the watt meter on
my
> Kenwood AT-200 antenna tuner bypassed to a dummy load indicates the K2 is
> pumping out a full 15 watts. Varying C1 while looking only at the K2 LCD,
I

> can get 1.0::1 SWR but the power out on the LCD registers 0.1 watts while
> the AT-200 wattmeter says the K2 is still pushing 15 watts to the dummy
> load. Varying C1 does not change the 15 watt output on the KAT200 watt
> metre. It always remains at a constant 15 watts.
>
> I then disassembled the KPA-100 circuit board from the heatsink. I checked
> that all the components you listed were the correct values and oriented
> properly i.e., D16 and D17. I checked the solder joints until my eyes
> crossed with a lamp having a magnifying lens in the centre of the
> fluorescent bulb. I found no solder bridges, unsoldered leads or poorly
> soldered solder pads. I thinks John's problem that he referred to in his
> post was a solder bridge between R24 and R26 but I found this junction was
> clean of any hint of a solder bridge. I found no protruding grounding

leads
> anywhere. I am quite sure but, not absolutely sure, that T4 is wound (12
> turns twisted wire counted inside the core), wired and soldered correctly
> with no leads shorting. The T4 solder pads are full with bright silvery
> solder, no craters and the solder flows through the holes to the top of
the
> circuit board.
>
> The only variable that I can see left is to pull T4, rewind and reinstall.
> However, before I do this, is there any other measurements, checks or
> procedures that I have overlooked or new ones that can be suggested?
>
> My career background is in the field of business and economics so I kind
of
> feel like I am an auto mechanic trying to diagnose and perform surgery on
a
> complex cardiology problem. That is to say, I really appreciate your help.
>
>

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

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Please help support this email list: http://www.qsl.net/donate.html

William Moore-5

Re: [K2] K2-100 Test and Alignment Issues

In reply to this post by Don Wilhelm-4

Don,

I am finally able to get back to my KPA-100 construction project and this
email is to complete this thread with the result.

Yes the problem was T4. I removed, rewound and replaced it. You were
correct, I had wound T4 backwards. With the correction I was able to easily
null the bridge to 12 millivolts. R26 and R27 required almost no adjustment
to set the correct values. The rest of the setup and test process went
perfectly.

So, to those who are or will be building the KPA-100, keep in mind that T4
must be wound exactly as illustrated and instructed in the manual.

Thanks again for your help, Don.

Bill, VE2WMA

-----Original Message-----
From: Don Wilhelm [mailto:[hidden email]]
Sent: Thursday, January 30, 2014 4:50 PM
To: William Moore; [hidden email]; [hidden email]; 'Mike Harris'
Subject: Re: [Elecraft] [K2] K2-100 Test and Alignment Issues

Bill,

Regarding T4, there is one other possibility that I did not mention before.
If the direction of the windings is not as shown in the manual, it will work
"backwards" which may be what you are observing.

As for the minimum voltage of 1.4 volts, that is WAY too high. The bridge
should null to less than 14 millivolts with 15 or 20 watts flowing through
it.

You could do a sanity check on it by attempting to null the bridge by
monitoring the DC voltage at U5 pin 3 rather than U5 pin 1. The voltage on
U5 pin 1 should be the same as at pin 3 if U5 is working OK.
If you still have a high voltage at U5 pin 3, then try doing the balance
(nulling) while monitoring U5 pin 5. If you can obtain a null at U5 pin 5,
then for certain T4 is wound in the wrong direction.

73,
Don W3FPR

>

______________________________________________________________
Elecraft mailing list
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