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[K2] TX Issue in Part III checks

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Brian Handy

[K2] TX Issue in Part III checks

Hi All,

I've been working on my K2 and I'm on the home stretch. I had to dabble a bit
to find a cold solder joint in the Part II checks, but eventually got a
home-brewed test oscillator to reach through on 40m! Quite happy with things so
far, and learning a lot.

I still have a lot to learn about the transmitter side though, that doesn't
work. When I first hit 'tune' in the Part III checks, I noticed high current on
the power supply, high current on the front panel, and changing the power level
didn't help, it was always high draw.

It didn't take much of this to zorch the PA finals and short things straight to
ground. Nothing worked until I pulled T3, and while I had the soldering out I
took out the PAs and started looking around and reading the mail archives.

I noted one suggestion from Don to someone else and checked the voltages on base
on the finals - both are around 0.65V, which I think is OK.

I realize things won't be quite the same without the PAs there and proper
feedback happening, but ... I then started going through all the voltages on the
RF board with TUNE on. Everything looked pretty much fine except for Q24 ~

Leg - Expected - Measured:
G - 0V - 5.6V
S - 1.2 - 2.5V
D - 13V - 0V

That doesn't look right at all to me. Exploring further, I started chasing VALC
down the rabbit hole.

Pin 2 of U8 (V PWR) seems to vary between 3.8-5V as I turn the PWR knob in
TUNE. I decided that was OK.

Pin 1 of U10A doesn't move around a lot, only up and down about 0.1V. Finally
the emitter of Q8 (V ALC) seems stuck at 7.4V.

I was firmly confused at this point, so went back and started checking Control
Board voltages per the page of expected readings in the back of the manual with
CAL FCTR turned on. Everything seems turned off when I do that and I'm seeing
pretty much 0V everywhere.

I'm a bit saturated at the moment, but thought I would ask if this sounds like
I'm on the right track, or if I have to get to poking elsewhere ...

Cheers and thanks in advance,

Brian Handy
AE7JW
Tokyo, Japan

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Don Wilhelm-4

Re: [K2] TX Issue in Part III checks

On 1/8/2011 10:44 PM, Brian Handy wrote:

> Hi All,
>
> I've been working on my K2 and I'm on the home stretch. I had to dabble a bit
> to find a cold solder joint in the Part II checks, but eventually got a
> home-brewed test oscillator to reach through on 40m! Quite happy with things so
> far, and learning a lot.
>
> I still have a lot to learn about the transmitter side though, that doesn't
> work. When I first hit 'tune' in the Part III checks, I noticed high current on
> the power supply, high current on the front panel, and changing the power level
> didn't help, it was always high draw.
>
> It didn't take much of this to zorch the PA finals and short things straight to
> ground. Nothing worked until I pulled T3, and while I had the soldering out I
> took out the PAs and started looking around and reading the mail archives.
>
> I noted one suggestion from Don to someone else and checked the voltages on base
> on the finals - both are around 0.65V, which I think is OK.
>
> I realize things won't be quite the same without the PAs there and proper
> feedback happening, but ... I then started going through all the voltages on the
> RF board with TUNE on. Everything looked pretty much fine except for Q24 ~
>
> Leg - Expected - Measured:
> G - 0V - 5.6V
> S - 1.2 - 2.5V
> D - 13V - 0V
>
> That doesn't look right at all to me. Exploring further, I started chasing VALC
> down the rabbit hole.
>
> Pin 2 of U8 (V PWR) seems to vary between 3.8-5V as I turn the PWR knob in
> TUNE. I decided that was OK.
>
> Pin 1 of U10A doesn't move around a lot, only up and down about 0.1V. Finally
> the emitter of Q8 (V ALC) seems stuck at 7.4V.
>
> I was firmly confused at this point, so went back and started checking Control
> Board voltages per the page of expected readings in the back of the manual with
> CAL FCTR turned on. Everything seems turned off when I do that and I'm seeing
> pretty much 0V everywhere.
>
> I'm a bit saturated at the moment, but thought I would ask if this sounds like
> I'm on the right track, or if I have to get to poking elsewhere ...
>
>
>
> Cheers and thanks in advance,
>
> Brian Handy
> AE7JW
> Tokyo, Japan
>
>
>
> ______________________________________________________________
> 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
>

______________________________________________________________
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] TX Issue in Part III checks

In reply to this post by Brian Handy

Brian,

The DC voltages on Q24 are based on a properly working K2 at the 5 watt
power level.
What you now have is a K2 that will not develop power to the RF
Detector, so the power control circuits will react to force the RF
voltages to their maximum - the control element for that is the VALC
voltage to Q24, and that will go to its maximum since there is zero
power detected.

I note that you measure zero volts at the drain of Q24, but VALC at the
source (CB emitter of Q8) is at 7.4 volts. Something is broken (not
soldered) between those two points because the only component between
the two is R98 which should not be drawing any current and therefore
should not have any voltage drop (given your situation with no power
output).

Look for unsoldered connections (don't forget the connectors) or solder
bridges in that signal path.
Look critically at you soldering - if the solder did not flow out to an
almost invisible edge on the solder pad, it is suspect, and the likely
cause is that the solder pad did not receive enough heat. Re-flow the
solder on all suspect connections using a hot (750 deg F) iron, and add
a bit of flux if necessary.

73,
Don W3FPR

On 1/8/2011 10:44 PM, Brian Handy wrote:

Don Wilhelm-4

Re: [K2] TX Issue in Part III checks

In reply to this post by Brian Handy

Brian,

Looking again at your Q24 measurements, I think you reversed the leads.
Check against the J310 basing diagram on the Schematic Key page and
remeasure.

5.6 volts on the drain is well within reason when there is no output -
VALC will go to its maximum value when there is no output sensed and
tries to make Q24 conduct harder so more BFO signal is delivered to the
Transmit Mixer. That is how the power control works - the conduction of
Q24 is the controlling element.

The voltages listed in the DC voltage chart are for a properly working
K2 at 5 watts output.

73,
Don W3FPR

On 1/8/2011 10:44 PM, Brian Handy wrote:

Don Wilhelm-4

Re: [K2] TX Issue in Part III checks

In reply to this post by Brian Handy

Brian,

I did not respond to your original problem of high current. A HiCur
problem combined with low or zero output normally indicates a problem in
the Low Pass filter and/or T4.

Your voltage on the base of the PA transistors is a bit high - I do not
like to see anything higher than 0.64 volts, so check the resistor
values connecting to Q11 and Q13. When you receive the K2PAKIT from
Elecraft, it will have replacement transistors for Q11 and Q13, and I
would suggest using them.

73,
Don W3FPR

On 1/8/2011 10:44 PM, Brian Handy wrote:

Brian Handy

Re: [K2] TX Issue in Part III checks

In reply to this post by Don Wilhelm-4

Don,

You're absolutely right, I checked again across R98 just to confirm and you are
on the money....5.6V at the drain. It seems possible this part may be working
fine.

I understand the voltages are going to be different, the whole feedback loop
isn't there. I'm just hopeful to identify the problem before nuking another set
of finals ... !

I'll keep looking. Thanks!

Brian AE7JW

----- Original Message ----
From: Don Wilhelm <[hidden email]>
To: Brian Handy <[hidden email]>
Cc: [hidden email]
Sent: Sun, January 9, 2011 11:27:58 PM
Subject: Re: [Elecraft] [K2] TX Issue in Part III checks

Brian,

Looking again at your Q24 measurements, I think you reversed the leads.
Check against the J310 basing diagram on the Schematic Key page and
remeasure.

5.6 volts on the drain is well within reason when there is no output -
VALC will go to its maximum value when there is no output sensed and
tries to make Q24 conduct harder so more BFO signal is delivered to the
Transmit Mixer. That is how the power control works - the conduction of
Q24 is the controlling element.

The voltages listed in the DC voltage chart are for a properly working
K2 at 5 watts output.

73,
Don W3FPR

On 1/8/2011 10:44 PM, Brian Handy wrote:

level
> didn't help, it was always high draw.
>
> It didn't take much of this to zorch the PA finals and short things straight
to

> ground. Nothing worked until I pulled T3, and while I had the soldering out I
> took out the PAs and started looking around and reading the mail archives.
>
> I noted one suggestion from Don to someone else and checked the voltages on
>base
> on the finals - both are around 0.65V, which I think is OK.
>
> I realize things won't be quite the same without the PAs there and proper
> feedback happening, but ... I then started going through all the voltages on
>the
> RF board with TUNE on. Everything looked pretty much fine except for Q24 ~
>
> Leg - Expected - Measured:
> G - 0V - 5.6V
> S - 1.2 - 2.5V
> D - 13V - 0V
>
> That doesn't look right at all to me. Exploring further, I started chasing
>VALC
> down the rabbit hole.
>
> Pin 2 of U8 (V PWR) seems to vary between 3.8-5V as I turn the PWR knob in
> TUNE. I decided that was OK.
>
> Pin 1 of U10A doesn't move around a lot, only up and down about 0.1V. Finally
> the emitter of Q8 (V ALC) seems stuck at 7.4V.
>
> I was firmly confused at this point, so went back and started checking Control
> Board voltages per the page of expected readings in the back of the manual

with

> CAL FCTR turned on. Everything seems turned off when I do that and I'm seeing
> pretty much 0V everywhere.
>
> I'm a bit saturated at the moment, but thought I would ask if this sounds like
> I'm on the right track, or if I have to get to poking elsewhere ...
>
>
>
> Cheers and thanks in advance,
>
> Brian Handy
> AE7JW
> Tokyo, Japan
>
>
>
> ______________________________________________________________
> 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
>

Brian Handy

Re: [K2] TX Issue in Part III checks

In reply to this post by Don Wilhelm-4

I checked the resistors, and they all look right.

Seems like the plan of attack is to replace Q11 and Q13, and have a hard look at
T4 ... I may rewind that just to take the moral high ground. Check the base
voltage on the finals again and make sure it's below 0.64 before installing the
high-ticket items.

Thanks a bunch!

Brian AE7JW

----- Original Message ----
From: Don Wilhelm <[hidden email]>
To: Brian Handy <[hidden email]>
Cc: [hidden email]
Sent: Sun, January 9, 2011 11:38:28 PM
Subject: Re: [Elecraft] [K2] TX Issue in Part III checks

Brian,

I did not respond to your original problem of high current. A HiCur
problem combined with low or zero output normally indicates a problem in
the Low Pass filter and/or T4.

Your voltage on the base of the PA transistors is a bit high - I do not
like to see anything higher than 0.64 volts, so check the resistor
values connecting to Q11 and Q13. When you receive the K2PAKIT from
Elecraft, it will have replacement transistors for Q11 and Q13, and I
would suggest using them.

73,
Don W3FPR

On 1/8/2011 10:44 PM, Brian Handy wrote:

level
> didn't help, it was always high draw.
>
> It didn't take much of this to zorch the PA finals and short things straight
to

with

Don Wilhelm-5

Re: [K2] TX Issue in Part III checks

In reply to this post by Brian Handy

Brian,

The PA transistors will normally take some abuse - for a short time, so
put them in and do a short test to see what happens - just be aware of
the conditions and keep the transmit times as short as possible while
still allowing some measurements to be taken. Everything in life is a
compromise, including this situation - TX time vs. potential abuse must
be compromised to come to the resolution of the problem.

73,
Don W3FPR

On 1/9/2011 7:01 PM, Brian Handy wrote:

> Don,
>
> You're absolutely right, I checked again across R98 just to confirm and you are
> on the money....5.6V at the drain. It seems possible this part may be working
> fine.
>
> I understand the voltages are going to be different, the whole feedback loop
> isn't there. I'm just hopeful to identify the problem before nuking another set
> of finals ... !
>
> I'll keep looking. Thanks!
>
> Brian AE7JW
>
>
>
>
> ----- Original Message ----
> From: Don Wilhelm<[hidden email]>
> To: Brian Handy<[hidden email]>
> Cc: [hidden email]
> Sent: Sun, January 9, 2011 11:27:58 PM
> Subject: Re: [Elecraft] [K2] TX Issue in Part III checks
>
> Brian,
>
> Looking again at your Q24 measurements, I think you reversed the leads.
> Check against the J310 basing diagram on the Schematic Key page and
> remeasure.
>
> 5.6 volts on the drain is well within reason when there is no output -
> VALC will go to its maximum value when there is no output sensed and
> tries to make Q24 conduct harder so more BFO signal is delivered to the
> Transmit Mixer. That is how the power control works - the conduction of
> Q24 is the controlling element.
>
> The voltages listed in the DC voltage chart are for a properly working
> K2 at 5 watts output.
>
> 73,
> Don W3FPR
>
> On 1/8/2011 10:44 PM, Brian Handy wrote:
>> Hi All,
>>
>> I've been working on my K2 and I'm on the home stretch. I had to dabble a bit
>> to find a cold solder joint in the Part II checks, but eventually got a
>> home-brewed test oscillator to reach through on 40m! Quite happy with things
>> so
>> far, and learning a lot.
>>
>> I still have a lot to learn about the transmitter side though, that doesn't
>> work. When I first hit 'tune' in the Part III checks, I noticed high current
>> on
>> the power supply, high current on the front panel, and changing the power
> level
>> didn't help, it was always high draw.
>>
>> It didn't take much of this to zorch the PA finals and short things straight
> to
>> ground. Nothing worked until I pulled T3, and while I had the soldering out I
>> took out the PAs and started looking around and reading the mail archives.
>>
>> I noted one suggestion from Don to someone else and checked the voltages on
>> base
>> on the finals - both are around 0.65V, which I think is OK.
>>
>> I realize things won't be quite the same without the PAs there and proper
>> feedback happening, but ... I then started going through all the voltages on
>> the
>> RF board with TUNE on. Everything looked pretty much fine except for Q24 ~
>>
>> Leg - Expected - Measured:
>> G - 0V - 5.6V
>> S - 1.2 - 2.5V
>> D - 13V - 0V
>>
>> That doesn't look right at all to me. Exploring further, I started chasing
>> VALC
>> down the rabbit hole.
>>
>> Pin 2 of U8 (V PWR) seems to vary between 3.8-5V as I turn the PWR knob in
>> TUNE. I decided that was OK.
>>
>> Pin 1 of U10A doesn't move around a lot, only up and down about 0.1V. Finally
>> the emitter of Q8 (V ALC) seems stuck at 7.4V.
>>
>> I was firmly confused at this point, so went back and started checking Control
>> Board voltages per the page of expected readings in the back of the manual
> with
>> CAL FCTR turned on. Everything seems turned off when I do that and I'm seeing
>> pretty much 0V everywhere.
>>
>> I'm a bit saturated at the moment, but thought I would ask if this sounds like
>> I'm on the right track, or if I have to get to poking elsewhere ...
>>
>>
>>
>> Cheers and thanks in advance,
>>
>> Brian Handy
>> AE7JW
>> Tokyo, Japan
>>
>>
>>
>> ______________________________________________________________
>> 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
>>
>
>
>
>