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Problem with KAT2 Bridge Null Adjustment

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Edward A. Dauer

Problem with KAT2 Bridge Null Adjustment

Advice requested for the following problem:

Completed and installed the KIO2. That works fine, so far as it has been tested with the outboard ("twins") KPA100 and KAT100. Next step was to put the amp and high power tuner aside and install a KAT2 in the base K2. [In case it matters, the K2 does not have the battery option.]

All went well with the KAT2 until the Bridge Null Adjustment. There are two strange symptoms:

First, adjusting C55 has no effect, and the display does not behave as it should. When Tune is held, the display first says HiCur, then it quickly changes to ATU and then, again quickly, it changes to 000 and stays there. Adjusting C55 to every possible position changes nothing. Each try produces the same display: about 2 seconds of HiCur, two seconds of ATU and then 000.

Second, the DC voltage at pin 1 of U4 is way off. In Receive Mode it reads 0.0, as it should. But in Tune mode, at 5 watts indicated, it reads only 0.69 DCV rather than the 3.0 to 4.0 expected.

I haven't put an external power meter on the rig yet but a 15-watt dummy load gets warm after a while so there does seem to be RF output.

I see no solder bridges, no cold joints, no breaks or shorts thatI can see. The plugs and sockets have been checked at least five times to assure they are properly aligned and properly assigned.

Any ideas, anyone? Thanks!

Ted, KN1CBR
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Don Wilhelm

Re: Problem with KAT2 Bridge Null Adjustment

Ted,

You will find the problem is with T1. It must be wound and installed
exactly as shown in the manual, and that includes the direction of the
winding.

Your K2 is likely putting out all the power it is capable of, so do
those TUNEs for only a short period or you will be replacing the PA
transistors.

73,
Don W3FPR

On 5/7/2016 12:02 PM, Dauer, Edward wrote:

> Advice requested for the following problem:
>
> Completed and installed the KIO2. That works fine, so far as it has been tested with the outboard ("twins") KPA100 and KAT100. Next step was to put the amp and high power tuner aside and install a KAT2 in the base K2. [In case it matters, the K2 does not have the battery option.]
>
> All went well with the KAT2 until the Bridge Null Adjustment. There are two strange symptoms:
>
> First, adjusting C55 has no effect, and the display does not behave as it should. When Tune is held, the display first says HiCur, then it quickly changes to ATU and then, again quickly, it changes to 000 and stays there. Adjusting C55 to every possible position changes nothing. Each try produces the same display: about 2 seconds of HiCur, two seconds of ATU and then 000.
>
> Second, the DC voltage at pin 1 of U4 is way off. In Receive Mode it reads 0.0, as it should. But in Tune mode, at 5 watts indicated, it reads only 0.69 DCV rather than the 3.0 to 4.0 expected.
>
> I haven't put an external power meter on the rig yet but a 15-watt dummy load gets warm after a while so there does seem to be RF output.
>
> I see no solder bridges, no cold joints, no breaks or shorts thatI can see. The plugs and sockets have been checked at least five times to assure they are properly aligned and properly assigned.
>
> Any ideas, anyone? Thanks!
>
> Ted, KN1CBR
> ______________________________________________________________
> 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
> Message delivered to [hidden email]
>

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Edward A. Dauer

Problem with KAT2 Bridge Null Adjustment

In reply to this post by Edward A. Dauer

Thanks, Don. I did check that, and redid all of T1’s solder joints. No
change. I was about to rewind T1 altogether when I decided to check the
archives. Using a search method earlier suggested by Phil, W7OX, I found
a post by you in 2013 answering the very same question. On reading it
something struck me — the person posing the question recited that he had
set the process up by, among other things, turning both R1 and R2 fully
clockwise. That hit me — I had read that instruction as full COUNTER
clockwise! I checked the manual again, and there it was - full clockwise.
So, after doing that the right way, and suffering some chagrin, all was
good. The U4 pin 1 voltage is a bit low at 2.8, but the null voltage gets
down to 006 using C55 as prescribed.

What you just wrote would have been exactly right - if I hadn’t been so
d*****d stupid. Thank you for not thinking that I could have been.

“RTFM” is now amended to read “RTFM-C” where C = carefully.

I am posting this on the reflector by way of self-discipline. If I didn’t
confess it publicly, I’d be less likely to learn from it.

Thanks, as always.

Ted, KN1CBR

On 5/7/16, 12:24 PM, "Don Wilhelm" <[hidden email]> wrote:

>Ted,
>
>You will find the problem is with T1. It must be wound and installed
>exactly as shown in the manual, and that includes the direction of the
>winding.
>
>Your K2 is likely putting out all the power it is capable of, so do
>those TUNEs for only a short period or you will be replacing the PA
>transistors.
>
>73,
>Don W3FPR
>
>On 5/7/2016 12:02 PM, Dauer, Edward wrote:
>> Advice requested for the following problem:
>>
>> Completed and installed the KIO2. That works fine, so far as it has
>>been tested with the outboard ("twins") KPA100 and KAT100. Next step
>>was to put the amp and high power tuner aside and install a KAT2 in the
>>base K2. [In case it matters, the K2 does not have the battery option.]
>>
>> All went well with the KAT2 until the Bridge Null Adjustment. There
>>are two strange symptoms:
>>
>> First, adjusting C55 has no effect, and the display does not behave as
>>it should. When Tune is held, the display first says HiCur, then it
>>quickly changes to ATU and then, again quickly, it changes to 000 and
>>stays there. Adjusting C55 to every possible position changes nothing.
>>Each try produces the same display: about 2 seconds of HiCur, two
>>seconds of ATU and then 000.
>>
>> Second, the DC voltage at pin 1 of U4 is way off. In Receive Mode it
>>reads 0.0, as it should. But in Tune mode, at 5 watts indicated, it
>>reads only 0.69 DCV rather than the 3.0 to 4.0 expected.
>>
>> I haven't put an external power meter on the rig yet but a 15-watt
>>dummy load gets warm after a while so there does seem to be RF output.
>>
>> I see no solder bridges, no cold joints, no breaks or shorts thatI can
>>see. The plugs and sockets have been checked at least five times to
>>assure they are properly aligned and properly assigned.
>>
>> Any ideas, anyone? Thanks!
>>
>> Ted, KN1CBR
>> ______________________________________________________________
>> 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
>> Message delivered to [hidden email]
>>
>