K2 - Low output during initial TX alignment

[JT Croteau]

During the initial TX alignment of my K2, I can't seem to get the
output power above 0.2W - it fluctuates between 0.1 and 0.2 and
doesn't change as I adjust L1 and L2.  I am, however, able to tune L1
and L2 for RX just fine.  I am showing 350 mV at my dummy load so some
RF seems to be getting through.

I don't see any obvious soldering problems and T1 through T4 appear to
be wound correctly.  I have not done any signal tracing yet but
initial voltage check of the driver and finals appear fine.  However,
I am concerned about the voltage of the drivers collector.  It jumps
up to 14V at transmit but it's supposed to be 13.3V.

I have to go out and buy a new DMM so I can do signal tracing (my
cheap DMM has fixed probes and I can't adapt them properly).  Any
other ideas before I dive into signal tracing?

Thanks

--
JT Croteau, N1ESE - Manchester, NH
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[JT Croteau]

On 9/4/07, John Graf <[hidden email]> wrote:
> One thing you might try is a relay reset.

Thanks John, this was one of the first things I tried.  No luck.  I've
done most of the checks in the 155 section of the troubleshooting
guide.  I'm at a loss as everything appears to be fine.

Back to it..

--
JT Croteau, N1ESE - Manchester, NH
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[Don Wilhelm-4]

JT,

The quickest and IMHO the easiest way to find the problem is to build up
the RF Probe (the parts were included with your K2 kit).  Then turn the
manual to Preparing for Transmit Signal Tracing in the troubleshooting
appendix.  Follow the steps until you find a place where you have
significantly lower RF voltage than expected - then *stop* because you
have located the failing stage.

Once you have found the failing stage, find it on the schematic and look
to see which components are used in that stage - check them all for
proper values and good soldering.

If that effort did not solve the problem, we can be of further help.  
Right now, the list of things that could possibly be wrong is very long
and we could only offer wild guesses.  Once narrowed to the failing
stage, the isolation of the failing part becomes much easier.

73,
Don W3FPR

JT Croteau wrote:

> On 9/4/07, John Graf <[hidden email]> wrote:
>  
>> One thing you might try is a relay reset.
>>    
>
> Thanks John, this was one of the first things I tried.  No luck.  I've
> done most of the checks in the 155 section of the troubleshooting
> guide.  I'm at a loss as everything appears to be fine.
>
> Back to it..
>
>  

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[JT Croteau]

On 9/4/07, Don Wilhelm <[hidden email]> wrote:
> The quickest and IMHO the easiest way to find the problem is to build up
> the RF Probe (the parts were included with your K2 kit).

Yeah, I need to go buy a new DMM as I have no way to connect the RF
probe to my current DMM.

However, I just checked the ALC circuit and found that VPWR is reading
high.  It is reading 4.9V on pin 2 of U8 (control board) during key
down.  According to the manual, this indicates a potential problem in
the RF detector stage.  I'm going to poke around the detector a bit
more and see if I can find any problems there.

--
JT Croteau, N1ESE - Manchester, NH
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[JT Croteau]

Don and others,

I just returned from buying a new DMM at RS and I didn't get very far
in signal tracing the transmitter before I started getting some
strange readings.

In my previous email, I mentioned that VPWR was reading high at 4.9V.
This can sometimes point to a problem in the RF output detector so I
checked all the components here and didn't find anything wrong so,
following the instructions, continued on with the signal tracing.

Transmit Mixer, Buffer, Band-Pass Filter, T-R Switch section - I am
finding some odd voltages here.  Voltages that do not match the
expected results listed.

These are all key-down voltages.

Xmit Mixer Output: 0.181  (Expected: 0.016)
Buffer Output: 2.05 (Expected: 0.200)
Band-Pass Filter Output: 0.444 (Expected: 0.030)
T-R Switch #1 Output: 0.439 (Expected: 0.029)

I am doing the signal tracing using 40M.

Do I need to worry about these?

Thanks

--
JT Croteau, N1ESE - Manchester, NH
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[Don Wilhelm-4]

JT,

If you have little or no RF output, do not be concerned about the early
stages having more RF voltage than is expected when the power is normal
(and that is your case).  Continue onward.

If the K2 senses no power output, VPWR will ramp up to a high level
trying to obtain more power output, and the RF voltage produced by the
*working* stages will be higher than normal until the proper amount of
RF is detected at the output.

An added note - measure the RF voltage across your dummy load.  If there
is lots of RF voltage there, then the transmitter is working and the
problem is with the detector (D9 and associated components) rather than
the transmitter stages, but if there really is no power output (or very
little) then look to the transmitter stages for the problem. - Do heed
the *if*s in the proceeding statement, they are very important.

Make the measurements in order and methodically as instructed in the
manual and the steps will lead you to the failing stage.

73,
Don W3FPR

JT Croteau wrote:

> Don and others,
>
> I just returned from buying a new DMM at RS and I didn't get very far
> in signal tracing the transmitter before I started getting some
> strange readings.
>
> In my previous email, I mentioned that VPWR was reading high at 4.9V.
> This can sometimes point to a problem in the RF output detector so I
> checked all the components here and didn't find anything wrong so,
> following the instructions, continued on with the signal tracing.
>
> Transmit Mixer, Buffer, Band-Pass Filter, T-R Switch section - I am
> finding some odd voltages here.  Voltages that do not match the
> expected results listed.
>
> These are all key-down voltages.
>
> Xmit Mixer Output: 0.181  (Expected: 0.016)
> Buffer Output: 2.05 (Expected: 0.200)
> Band-Pass Filter Output: 0.444 (Expected: 0.030)
> T-R Switch #1 Output: 0.439 (Expected: 0.029)
>
> I am doing the signal tracing using 40M.
>
> Do I need to worry about these?
>
> Thanks
>
>  

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[JT Croteau]

On 9/4/07, Don Wilhelm <[hidden email]> wrote:
> If you have little or no RF output

Exactly, this is my problem.  Continuing onward.

> An added note - measure the RF voltage across your dummy load.

I'm not seeing any RF voltage across the dummy load.  I am only seeing
about 350 mV of DC voltage across the DL1 on key-down.

I have just completed the Pre-driver, Driver, and PA signal tracing.
Things are very interesting here.  Driver voltages are very high,
especially the output voltage but the PA Inputs and Detector Input are
very low.

Pre-Driver Output: 1.841 V (Expected: 0.120 V)
Driver Input: 0.355 V (Expected: 0.026 V)
Driver Output: 8.04 V (Expected: 1.8 V)
PA Input (Q7): 0.030 V (Expected: 0.38 V)
PA Input (Q8): 0.002 V (Expected: 0.38 V)
RF Detector Input: 0.040 V (Expected: 2.0 V)

Does this mean I have a problem between the Driver and PA or do I have
a different problem area due the the high output of the Driver?

Thanks

--
JT Croteau, N1ESE - Manchester, NH
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[Don Wilhelm-4]

JT,

Fine information.  You have a problem between the collector of Q6 and
the bases of Q7 and Q8.

Your next step is to turn to the schematic RF Board sheet 4 of 4 and
locate Q6, Q7 and Q8 and all the components between them.  Check all for
good soldering and be certain the 3 and 4 (green) leads of T2 are well
tinned and soldered.
You should have zero ohms between the end of R54 and the end of R53 (the
ends that are connected to the T2 winding) - if not, T2 is not well
tinned and soldered - if that is the problem, remove T2, re-strip the
leads and re-install it, it is next to impossible to correct a poor lead
tinning condition with the leads connected on the board (I have tried
that and failed many times).  The T2 3/4 winding is the most likely
source of your problem.

If you want to check  the components with your ohmmeter, you will have
to lift one end of many of the components (RF Chokes and resistors),
with the RF chokes paralleling the resistors it is just not possible to
check the actual resistance in-circuit, but you can usually trust the
color code markings - but be certain the correct resistor is in the
right place.

73,
Don W3FPR



JT Croteau wrote:

> On 9/4/07, Don Wilhelm <[hidden email]> wrote:
>  
>> If you have little or no RF output
>>    
>
> Exactly, this is my problem.  Continuing onward.
>
>  
>> An added note - measure the RF voltage across your dummy load.
>>    
>
> I'm not seeing any RF voltage across the dummy load.  I am only seeing
> about 350 mV of DC voltage across the DL1 on key-down.
>
> I have just completed the Pre-driver, Driver, and PA signal tracing.
> Things are very interesting here.  Driver voltages are very high,
> especially the output voltage but the PA Inputs and Detector Input are
> very low.
>
> Pre-Driver Output: 1.841 V (Expected: 0.120 V)
> Driver Input: 0.355 V (Expected: 0.026 V)
> Driver Output: 8.04 V (Expected: 1.8 V)
> PA Input (Q7): 0.030 V (Expected: 0.38 V)
> PA Input (Q8): 0.002 V (Expected: 0.38 V)
> RF Detector Input: 0.040 V (Expected: 2.0 V)
>
> Does this mean I have a problem between the Driver and PA or do I have
> a different problem area due the the high output of the Driver?
>
> Thanks
>
>  

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[JT Croteau]

On 9/4/07, Don Wilhelm <[hidden email]> wrote:
> You should have zero ohms between the end of R54 and the end
> of R53 (the ends that are connected to the T2 winding) - if not, T2
> is not well tinned and soldered

Well, I am showing 12 ohms so I guess I'll have to take another look
at this bugger.

Thanks

--
JT Croteau, N1ESE - Manchester, NH
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[JT Croteau]

Holy cow!  I got it to work!

It was definitely a improperly tinned green lead on T2.  So much for
buying pre-wound/tinned 'roids to save me some grief.  Heh.

Thanks Don.  What a relief.  Time to button it back up and continue
40M TX alignment.

--
JT Croteau, N1ESE - Manchester, NH
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[Don Wilhelm-4]

JT,

The green leads of T2 are meant to be long so they can be routed under
the core as shown in the manual.  Mychael does a good job of tinning the
leads for the proper length, but if you tug on them during installation,
you can pull the untinned portion of the lead into the hole and the
result is a PTTL (poorly tinned solder lead).  If T2 is mounted right
down on the board, there is often a drop-off of maximum power on the
higher bands.  Should you encounter that difficulty, consider re-winding
T2 as a first solution and mounting it 1/8 inch above the board.

73,
Don W3FPR

JT Croteau wrote:
> Holy cow!  I got it to work!
>
> It was definitely a improperly tinned green lead on T2.  So much for
> buying pre-wound/tinned 'roids to save me some grief.  Heh.
>
> Thanks Don.  What a relief.  Time to button it back up and continue
> 40M TX alignment.
>
>  
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[Mychael Morohovich]

Hi, John-

Since I am the fellow who provides the pre wound toroids, I would like to
offer that I do include a note with my K2 sets instructing the builder not
to pull the leads too tightly while installing K2-T2 . Its design is a
little unusual insofar that the toroid is spaced slightly up off of the
PCB, its green secondary leads hidden under the core. I tin most parts up
to or onto the core itself, and with this part care must be taken not to
distort how the lengthy green leads are positioned since this could result
in pulling some enamel into the PCB.

73,

Mychael AA3WF
K2#1025


> It was definitely a improperly tinned green lead on T2.  So much for
> buying pre-wound/tinned 'roids to save me some grief.  Heh.
> JT Croteau, N1ESE - Manchester, NH




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[JT Croteau]

On 9/4/07, Mychael Morohovich <[hidden email]> wrote:
> I would like to offer that I do include a note with my K2 sets
> instructing the builder not to pull the leads too tightly while
> installing K2-T2.

Hi Mychael.

I didn't mean to sound insulting or belittle your service in anyway.
However, looking back at the email and thinking about how quickly I
wrote it, I can see how it can be construed as such.   So please
accept my apologies.

The incorrect installation of T2 was definitely my fault by pulling
the leads too tight.  However, had I taken to time to wind and tin the
toroids myself, I may have been a bit more patient with their actual
installation as well.  Who knows though, maybe not.

Thanks again.

--
JT Croteau, N1ESE - Manchester, NH
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[Mychael Morohovich]

Hi, John-

Thank you for your post, as well as for the use of my service. In rereading
what I had written, I believe that my post might have come with a terseness
that I had not intended, so my apologies as well. K2-T2 is a little tricky
to get right, as is communicating with the written word it would seem- hi!

73,

Mychael AA3WF
K2 #1025




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