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NG0R - K2 Build/Alignment Issue

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John Hoaglun-2

NG0R - K2 Build/Alignment Issue

Hello,

I am working on the receiver and transmitter alignment at the end of the build process. I used a signal generator to peak up all of the band pass filters and they works as expected. When I try to check the transmit alignment I am not getting to the proper power output. Even peaked up for max smoke I am not getting the proper power out.

3.750mhz 2.5w Hi Cur

7.100mhz 6.1w Hi Cur

10.100mhz 0.3w Hi Cur

14.100mhz 0.3w Hi Cur

18.100mhz 9.5w

21.100mhz 4.1w

24.900mhz 0.5w

28.200mhz 6.0w

All of these were tested with a external wattmeter & the internal meter. I also validated that dummy load not the issue by testing this using a triband antenna on 20m and the measurements matched.

Do you have any suggests on some places to look?

It is possible that it could be an issue with the low pass filters but I find it hard to believe that I messed up all five filters. You would think that at least one of them would be ok. :-)

Thoughts?

Please respond direct as well as to the list... I get the digest version so it could be a while before I see next digest email.

Thanks, JH

-----------------------------

John Hoaglun

NG0R - EN25

http://www.hoaglun.com

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Don Wilhelm-4

Re: NG0R - K2 Build/Alignment Issue

JH,

I would definitely say the 20/30 meter low pass filter needs to be
checked. Low power output combined with HI CURR messages normally
indicate a low pass filter problem.
I am not certain how you are getting power output on 10 meters, but not
on 12. That may be a bandpass filter problem.
The low power on 80 may be a bandpass problem too, or it could be a
lowpass filter problem - that lowpass is only used on 80.

Look carefully at all the toroid leads - there should be a bit of tinned
lead above the top of the board, and when you look down on the soldered
connection, the joints should look like mountains, but not volcanoes.
If there is a ring around the wire lead, it was not properly tinned -
remove it, clean the lead and re-tin.

Since some of the bands transmit at 6 watts, that may be an indication
that only one of the PA transistors is working. Do the Hi Curr messages
on 40m cease if you set the power at 5 watts? If so, suspect one of the
PA transistors is bad.

Repeat the transmit tuning for the bandpass filters for all bands that
you can obtain some output - you should find a definite peak, if you do
not, that is an indication of a bandpass filter problem.

If you don't find anything substantial in the above steps, build the RF
probe from the parts that came with your K2 and do the Transmit Signal
Tracing steps in Appendix E of the manual to find the failing stage.
Once you identify that stage, do the DC Voltages checks for that stage.
If you have not figured out the failure by that time, ask about it again
on the reflector.

73,
Don W3FPR

John Hoaglun wrote:

> Hello,
>
> I am working on the receiver and transmitter alignment at the end of
> the build process. I used a signal generator to peak up all of the
> band pass filters and they works as expected. When I try to check the
> transmit alignment I am not getting to the proper power output. Even
> peaked up for max smoke I am not getting the proper power out.
>
> 3.750mhz 2.5w Hi Cur
> 7.100mhz 6.1w Hi Cur
> 10.100mhz 0.3w Hi Cur
> 14.100mhz 0.3w Hi Cur
> 18.100mhz 9.5w
> 21.100mhz 4.1w
> 24.900mhz 0.5w
> 28.200mhz 6.0w
>
> All of these were tested with a external wattmeter & the internal
> meter. I also validated that dummy load not the issue by testing this
> using a triband antenna on 20m and the measurements matched.
>
> Do you have any suggests on some places to look?
>
> It is possible that it could be an issue with the low pass filters but
> I find it hard to believe that I messed up all five filters. You would
> think that at least one of them would be ok. :-)
>
> Thoughts?
>
> Please respond direct as well as to the list... I get the digest
> version so it could be a while before I see next digest email.
>
> Thanks, JH
>
> -----------------------------
> John Hoaglun
> NG0R - EN25
> http://www.hoaglun.com
>
> ------------------------------------------------------------------------
>
> _______________________________________________
> Elecraft mailing list
> Post to: [hidden email]
> You must be a subscriber to post to the list.
> Subscriber Info (Addr. Change, sub, unsub etc.):
> http://mailman.qth.net/mailman/listinfo/elecraft
>
> Help: http://mailman.qth.net/subscribers.htm
> Elecraft web page: http://www.elecraft.com
> ------------------------------------------------------------------------
>
>
> No virus found in this incoming message.
> Checked by AVG - http://www.avg.com
> Version: 8.0.176 / Virus Database: 270.9.13/1828 - Release Date: 12/4/2008 8:05 AM
>
>

John Hoaglun-2

RE: NG0R - K2 Build/Alignment Issue

K2 gurus:

I got a note from Gary (support) and Don (w3fpr) with some ideas.

--I checked the low pass filters and the number of turns.
--I validated that T4 is oriented the right direction
--No burnt relays
--8R/8T are ~8vdc (R-7.87/T-7.815)
--8R on transmit goes to 0.245vdc
--I clipped W1 to test for PA feedback (no change)
--I removed the bottom panels and cleaned up a couple of joints as a CYA
--Removed and rewound LP for 80m
--Checked & resolder the connections of toroids for 20/30, 15/17, & 40
--Repeaked (on receive) all of the band pass filters with a signal generator
--Repeaked (on transmit) all of the band pass filters

I made some progress:

--Freq-----1 Test----1 Msg----2 Test----2 Msg
3.750mhz 2.5w Hi Cur 2.3w Hi Cur
7.100mhz 6.1w Hi Cur 6.6w Hi Cur
10.100mhz 0.3w Hi Cur 4.9w Hi Cur
14.100mhz 0.3w Hi Cur 5.7w
18.100mhz 9.5w 7.3w
21.100mhz 4.1w 5.0w
24.900mhz 0.5w 4.9w
28.200mhz 6.0w 6.3w

As you can see I am now getting ~5w on all bands except for 80m. I suspect
that the toroid cleanup might have been part of the answer for 20/30 and
tweaking the band pass brought 10/12 into better alignment.

On the three bands that I get a high current message it appears at the peak
power out and does go away if the power is reduced. Any chance that I am
only seeing power out of Q7 or Q8 instead of both of them?

Thanks, JH

-----------------------------
John Hoaglun
NG0R - EN25
http://www.hoaglun.com

-----Original Message-----
From: Don Wilhelm

--Snip--

I would definitely say the 20/30 meter low pass filter needs to be checked.
Low power output combined with HI CURR messages normally indicate a low pass
filter problem.

I am not certain how you are getting power output on 10 meters, but not on
12. That may be a bandpass filter problem.
The low power on 80 may be a bandpass problem too, or it could be a lowpass
filter problem - that lowpass is only used on 80.

--Snip--

Since some of the bands transmit at 6 watts, that may be an indication that
only one of the PA transistors is working. Do the Hi Curr messages on 40m
cease if you set the power at 5 watts? If so, suspect one of the PA
transistors is bad.

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Elecraft mailing list
Post to: [hidden email]
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Don Wilhelm-4

Re: NG0R - K2 Build/Alignment Issue

JH,

Yes, based on the data you have after the 'clean-up' tasks, I do suspect
that you have one of the PA transistors that are not working.

Try one more thing - set CAL CUR at 3.50 Amps and try again with the
power set to 5 watts only - you are likely to see no Hi Cur messages if
indeed one of the PA transistors is not working.

Check to see if you bent the leads too sharply and one has broken for
you. If that is the case, perhaps you can solder a wire 'splice' over
the break and be working again quickly. If not, you can request a
replacement set of PA transistors from [hidden email].

73,
Don W3FPR

John Hoaglun wrote:

> K2 gurus:
>
> I got a note from Gary (support) and Don (w3fpr) with some ideas.
>
> --I checked the low pass filters and the number of turns.
> --I validated that T4 is oriented the right direction
> --No burnt relays
> --8R/8T are ~8vdc (R-7.87/T-7.815)
> --8R on transmit goes to 0.245vdc
> --I clipped W1 to test for PA feedback (no change)
> --I removed the bottom panels and cleaned up a couple of joints as a CYA
> --Removed and rewound LP for 80m
> --Checked & resolder the connections of toroids for 20/30, 15/17, & 40
> --Repeaked (on receive) all of the band pass filters with a signal generator
> --Repeaked (on transmit) all of the band pass filters
>
> I made some progress:
>
> --Freq-----1 Test----1 Msg----2 Test----2 Msg
> 3.750mhz 2.5w Hi Cur 2.3w Hi Cur
> 7.100mhz 6.1w Hi Cur 6.6w Hi Cur
> 10.100mhz 0.3w Hi Cur 4.9w Hi Cur
> 14.100mhz 0.3w Hi Cur 5.7w
> 18.100mhz 9.5w 7.3w
> 21.100mhz 4.1w 5.0w
> 24.900mhz 0.5w 4.9w
> 28.200mhz 6.0w 6.3w
>
> As you can see I am now getting ~5w on all bands except for 80m. I suspect
> that the toroid cleanup might have been part of the answer for 20/30 and
> tweaking the band pass brought 10/12 into better alignment.
>
> On the three bands that I get a high current message it appears at the peak
> power out and does go away if the power is reduced. Any chance that I am
> only seeing power out of Q7 or Q8 instead of both of them?
>
> Thanks, JH
>
> -----------------------------
> John Hoaglun
> NG0R - EN25
> http://www.hoaglun.com
>
>
> -----Original Message-----
> From: Don Wilhelm
>
> --Snip--
>
> I would definitely say the 20/30 meter low pass filter needs to be checked.
> Low power output combined with HI CURR messages normally indicate a low pass
> filter problem.
>
> I am not certain how you are getting power output on 10 meters, but not on
> 12. That may be a bandpass filter problem.
> The low power on 80 may be a bandpass problem too, or it could be a lowpass
> filter problem - that lowpass is only used on 80.
>
> --Snip--
>
> Since some of the bands transmit at 6 watts, that may be an indication that
> only one of the PA transistors is working. Do the Hi Curr messages on 40m
> cease if you set the power at 5 watts? If so, suspect one of the PA
> transistors is bad.
>
>
> _______________________________________________
> Elecraft mailing list
> Post to: [hidden email]
> You must be a subscriber to post to the list.
> Subscriber Info (Addr. Change, sub, unsub etc.):
> http://mailman.qth.net/mailman/listinfo/elecraft
>
> Help: http://mailman.qth.net/subscribers.htm
> Elecraft web page: http://www.elecraft.com
> ------------------------------------------------------------------------
>
>
> No virus found in this incoming message.
> Checked by AVG - http://www.avg.com
> Version: 8.0.176 / Virus Database: 270.9.13/1828 - Release Date: 12/4/2008 8:05 AM
>
>

John Hoaglun-2

Re: NG0R - K2 Build/Alignment Issue

In reply to this post by John Hoaglun-2

K2 Gurus... still looking for your magic. :-)

Based upon some feedback from Gary I went poking around the radio with the RF probe. I looked at the low pass filters and relays to see if I stray RF floating around because maybe a relay was stuck. I only say RF where I expected it.

I tried to retune the 80m bandpass filters with the same result.

I decided to poke around the Q7/Q8 finals at low power with the probe:

14.100mhz @ ~1w

Q7 Base 154mv

Q7 Collector 5.56v

Q7 Emitter 24mv

Q8 Base 114mv

Q8 Collector 5.56v

Q8 Emitter .4mv

I am not electronics genius but it sure appears that I am seeing RF from both transistors.

Is that much variance in the Base/Emitter between Q7 and Q8 normal? That is the closet thing I can come with for a discovery on my own tonight. (I ordered another set of Q7/Q8 earlier today as a CYA.. but I think that was an unneeded exercise.)

Last nights testing:

--Freq-----1 Test----1 Msg----2 Test----2 Msg
3.750mhz    2.5w    Hi Cur   2.3w      Hi Cur
7.100mhz    6.1w    Hi Cur   6.6w      Hi Cur
10.100mhz    0.3w    Hi Cur   4.9w      Hi Cur
14.100mhz    0.3w    Hi Cur   5.7w
18.100mhz    9.5w             7.3w
21.100mhz    4.1w             5.0w
24.900mhz    0.5w             4.9w
28.200mhz    6.0w             6.3w

Thanks, JH

-----------------------------

John Hoaglun

NG0R - EN25

http://www.hoaglun.com

Don Wilhelm-4

Re: NG0R - K2 Build/Alignment Issue

John,

It is difficult to say because the 2 transistors are tightly coupled.

One thing I can say is that the emitter voltage is suspect. Both
emitters are tied to the ground plane and should be at the same RF
potential. OTOH, the difference between 24mv and 0.4mv could be
expained away based on RF pickup by the ground lead on the RF Probe - I
don't know how long you probe ground lead is, but if it is much more
than 3 inches, it is suspect too.

The best method of analysis is substitution, but that means changing the
PA transistors. Wait until you have the replacement transistors in hand
and just change them. If that does not fix the situation, look more
carefully at T5, T4, and the low pass filters.

I can explain the HI Cur messages by going into detail about how the K2
controls power output, but for now, 'just believe' that one failing PA
transistor can cause that as well as power output at approximately half
the expected value.

73,
Don W3FPR

John Hoaglun wrote:

> K2 Gurus... still looking for your magic. :-)
>
> Based upon some feedback from Gary I went poking around the radio with
> the RF probe. I looked at the low pass filters and relays to see if I
> stray RF floating around because maybe a relay was stuck. I only say
> RF where I expected it.
>
> I tried to retune the 80m bandpass filters with the same result.
>
> I decided to poke around the Q7/Q8 finals at low power with the probe:
> 14.100mhz @ ~1w
>
> Q7 Base 154mv
> Q7 Collector 5.56v
> Q7 Emitter 24mv
>
> Q8 Base 114mv
> Q8 Collector 5.56v
> Q8 Emitter .4mv
>
> I am not electronics genius but it sure appears that I am seeing RF
> from both transistors.
>
> Is that much variance in the Base/Emitter between Q7 and Q8 normal?
> That is the closet thing I can come with for a discovery on my own
> tonight. (I ordered another set of Q7/Q8 earlier today as a CYA.. but
> I think that was an unneeded exercise.)
>
>
> Last nights testing:
>
> --Freq-----1 Test----1 Msg----2 Test----2 Msg
> 3.750mhz 2.5w Hi Cur 2.3w Hi Cur
> 7.100mhz 6.1w Hi Cur 6.6w Hi Cur
> 10.100mhz 0.3w Hi Cur 4.9w Hi Cur
> 14.100mhz 0.3w Hi Cur 5.7w
> 18.100mhz 9.5w 7.3w
> 21.100mhz 4.1w 5.0w
> 24.900mhz 0.5w 4.9w
> 28.200mhz 6.0w 6.3w
>
> Thanks, JH
>
> -----------------------------
> John Hoaglun
> NG0R - EN25
> http://www.hoaglun.com
>
> ------------------------------------------------------------------------
>
> _______________________________________________
> Elecraft mailing list
> Post to: [hidden email]
> You must be a subscriber to post to the list.
> Subscriber Info (Addr. Change, sub, unsub etc.):
> http://mailman.qth.net/mailman/listinfo/elecraft
>
> Help: http://mailman.qth.net/subscribers.htm
> Elecraft web page: http://www.elecraft.com
> ------------------------------------------------------------------------
>
>
> No virus found in this incoming message.
> Checked by AVG - http://www.avg.com
> Version: 8.0.176 / Virus Database: 270.9.14/1832 - Release Date: 12/5/2008 9:57 AM
>
>

John Hoaglun-2

RE: NG0R - K2 Build/Alignment Issue

Hi Don & the group,

I replaced Q7, Q8, and Q11, and Q13 this morning. The initial smoke test is
showing the same results. I am probably going to take the radio to a
friend's house that has an o-scope and he is better at electrical theory
that I am.

Your T5 is an interesting comment. Are there artifacts that we can check for
around T5?

Plan for today:
1. I am going to go repeak the band pass filters on receive and transmit.
2. Retest band by band. (I will probably still have an issue)
3. Remove the W1 jumper, solder a small piece of coax jumper into place and
test independent of the Low Pass Filters.

I really need to determine if the problem is in one of three areas: Band
Pass, RF & bias, or LowPass.

Keep your thoughts coming... so far this is kicking my butt.

Thanks, JH

-----------------------------
John Hoaglun
NG0R - EN25
http://www.hoaglun.com

-----Original Message-----
From: Don Wilhelm [mailto:[hidden email]]

John,

It is difficult to say because the 2 transistors are tightly coupled.

One thing I can say is that the emitter voltage is suspect. Both emitters
are tied to the ground plane and should be at the same RF potential. OTOH,
the difference between 24mv and 0.4mv could be expained away based on RF
pickup by the ground lead on the RF Probe - I don't know how long you probe
ground lead is, but if it is much more than 3 inches, it is suspect too.

The best method of analysis is substitution, but that means changing the PA
transistors. Wait until you have the replacement transistors in hand and
just change them. If that does not fix the situation, look more carefully
at T5, T4, and the low pass filters.

I can explain the HI Cur messages by going into detail about how the K2
controls power output, but for now, 'just believe' that one failing PA
transistor can cause that as well as power output at approximately half the
expected value.

73,
Don W3FPR

John Hoaglun wrote:

Don Wilhelm-4

Re: NG0R - K2 Build/Alignment Issue

John,

I just looked back at your prior Q7/Q8 measurements and noticed that you
have less than 6 volts on the collectors - sorry that I did not notice
that before. That may be the sole reason for your low power output.
When the voltage is low, a Hi Cur message will often appear, and the
output power may be low.

The reason -- in the way that the K2 controls power, it operates in a
closed loop that is looking for the requested power output - if the
actual power is low, the K2 increases the drive to attempt to develop
more power. At the same time, if the voltage to the PA transistors is
low, more current must be drawn to produce the requested power (P = V x
I -- reduce the voltage and the current must increase to maintain equal
power).

OK, here is my way of getting to the bottom of a problem like yours
(part thoughts/questions, part things to measure and do):

For some reason, the Q7/Q8 collector voltage is low during transmit.
Are you using a good power supply capable of more than 3 Amps output
while maintaining a voltage of 12 to 14 volts? Are you using a power
cord with an adequate size wire? I recommend #16 gauge, but #18 will
likely be OK (but no smaller). Are the connections to your power supply
tight? How about the soldering of the plug that goes into the K2? If
there are any doubts, measure the end to end resistance of the power
cord (measure both the positive and negative leads - both are involved
in conducting the current).

Check the voltage at the power supply output during transmit - if the
voltage drops substantially there, you can blame the power supply (and
there may be nothing wrong with the K2). Should you find yourself in a
situation with a bad power supply and no suitable replacement, borrow
the battery from your lawn tractor or something of that sort and run the
K2 from that to test.

If the power supply voltage is holding up (at least 11.5 volts, prefer
more) during transmit, you will have to find the place in the K2 where
the large voltage drop is occurring. During transmit, measure the
voltage at these points in order:
1) The center of the input power jack (voltage should be the same as the
supply less any drop in the wire).
2) The Anode of D10 (should be the same as above)
3) The Cathode of D10 (should be 0.1 to 0.2 volts less than above)
4) The Cathode of D12 (same as cathode of D10, but this checks the
switch too).
5) The 'C' and 'B' pads of T3 (same as the cathode of D12)
6) The 'A' and 'D' pads of T3 (more than 0.2 volt less here indicates
improper soldering of T3).
7) The collectors of Q7 and Q8 (should be the same as #6 above).

If all is working correctly, you should have a voltage on the Q7/Q8
collectors that is only 0.3 to 0.5 volts less than at your power supply
output. Find out where the severe voltage drop is occurring and correct it.

73,
Don W3FPR

John Hoaglun wrote:

> Hi Don & the group,
>
> I replaced Q7, Q8, and Q11, and Q13 this morning. The initial smoke test is
> showing the same results. I am probably going to take the radio to a
> friend's house that has an o-scope and he is better at electrical theory
> that I am.
>
> Your T5 is an interesting comment. Are there artifacts that we can check for
> around T5?
>
>
> Plan for today:
> 1. I am going to go repeak the band pass filters on receive and transmit.
> 2. Retest band by band. (I will probably still have an issue)
> 3. Remove the W1 jumper, solder a small piece of coax jumper into place and
> test independent of the Low Pass Filters.
>
> I really need to determine if the problem is in one of three areas: Band
> Pass, RF & bias, or LowPass.
>
> Keep your thoughts coming... so far this is kicking my butt.
>
> Thanks, JH
>
> -----------------------------
> John Hoaglun
> NG0R - EN25
> http://www.hoaglun.com
>
>
> -----Original Message-----
> From: Don Wilhelm [mailto:[hidden email]]
>
> John,
>
> It is difficult to say because the 2 transistors are tightly coupled.
>
> One thing I can say is that the emitter voltage is suspect. Both emitters
> are tied to the ground plane and should be at the same RF potential. OTOH,
> the difference between 24mv and 0.4mv could be expained away based on RF
> pickup by the ground lead on the RF Probe - I don't know how long you probe
> ground lead is, but if it is much more than 3 inches, it is suspect too.
>
> The best method of analysis is substitution, but that means changing the PA
> transistors. Wait until you have the replacement transistors in hand and
> just change them. If that does not fix the situation, look more carefully
> at T5, T4, and the low pass filters.
>
> I can explain the HI Cur messages by going into detail about how the K2
> controls power output, but for now, 'just believe' that one failing PA
> transistor can cause that as well as power output at approximately half the
> expected value.
>
> 73,
> Don W3FPR
>
> John Hoaglun wrote:
>
>> K2 Gurus... still looking for your magic. :-)
>>
>> Based upon some feedback from Gary I went poking around the radio with
>> the RF probe. I looked at the low pass filters and relays to see if I
>> stray RF floating around because maybe a relay was stuck. I only saw
>> RF where I expected it.
>>
>> I tried to retune the 80m bandpass filters with the same result.
>>
>> I decided to poke around the Q7/Q8 finals at low power with the probe:
>> 14.100mhz @ ~1w
>>
>> Q7 Base 154mv
>> Q7 Collector 5.56v
>> Q7 Emitter 24mv
>>
>> Q8 Base 114mv
>> Q8 Collector 5.56v
>> Q8 Emitter .4mv
>>
>> I am not electronics genius but it sure appears that I am seeing RF
>> from both transistors.
>>
>> Is that much variance in the Base/Emitter between Q7 and Q8 normal?
>> That is the closet thing I can come with for a discovery on my own
>> tonight. (I ordered another set of Q7/Q8 earlier today as a CYA.. but
>> I think that was an unneeded exercise.)
>>
>>
>> Last nights testing:
>>
>> --Freq-----1 Test----1 Msg----2 Test----2 Msg
>> 3.750mhz 2.5w Hi Cur 2.3w Hi Cur
>> 7.100mhz 6.1w Hi Cur 6.6w Hi Cur
>> 10.100mhz 0.3w Hi Cur 4.9w Hi Cur
>> 14.100mhz 0.3w Hi Cur 5.7w
>> 18.100mhz 9.5w 7.3w
>> 21.100mhz 4.1w 5.0w
>> 24.900mhz 0.5w 4.9w
>> 28.200mhz 6.0w 6.3w
>>
>