Elecraft

VCO Alignment

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Jim K4ZMV

VCO Alignment

Hello.

I am building K2 #5731 and I have run into two problems. The first, and most serious, is in VCO alignment. When moving L30, the voltage at the left end of R30 does not change from 8.03vdc. I have been through the entire range of L30, very carefully, with no change. I pulled out T5 and rewound it. It is as nearly perfect as I can get it. When I measure vdc on T5, I see approximately 0.01vdc on 1 and 2 and 2.65 on 3 and 4. I checked voltages on U4 and U6 and they are in the range of the table in the back of the manual. I've checked all the components installed and the soldering. This is my second K2 and I have been a lot more careful. I'm stumped. Anybody got any ideas.

The second thing is that parts of the mode indicator on the display have become intermittent. Any ideas on that?

Thanks.

Jim, K4ZMV
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Don Wilhelm-3

RE: VCO Alignment

Jim,

The most common source of problems with the PLL or VCO is a solder bridge on
the thermistor board. There are other possible sources, but check there
first. You can often get to the back of the thermistor board by removing
the front panel and the control board.

You intermittent display is most likely an unsoldered connection (or poorly
soldered) - usually on the front panel itself.

So check the soldering first, then re-check the soldering, and when that is
done, check the soldering - that is the most common failure and misplaced
components runs in second place. Bad components are way down the list.

73,
Don W3FPR

> -----Original Message-----
>
> I am building K2 #5731 and I have run into two problems. The
> first, and most serious, is in VCO alignment. When moving L30,
> the voltage at the left end of R30 does not change from 8.03vdc.
> I have been through the entire range of L30, very carefully, with
> no change. I pulled out T5 and rewound it. It is as nearly
> perfect as I can get it. When I measure vdc on T5, I see
> approximately 0.01vdc on 1 and 2 and 2.65 on 3 and 4. I checked
> voltages on U4 and U6 and they are in the range of the table in
> the back of the manual. I've checked all the components
> installed and the soldering. This is my second K2 and I have
> been a lot more careful. I'm stumped. Anybody got any ideas.
>
> The second thing is that parts of the mode indicator on the
> display have become intermittent. Any ideas on that?
>
> Thanks.
>
> Jim, K4ZMV
>

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Jim K4ZMV

Re: VCO Alignment

Thanks, Don.

Found the intermittent display problem. And, it was a solder problem. I
checked the thermistor and all checks OK there. I'll keep looking ... think
I have ruled out the misplaced or misused component option. I'll just go
through all the RF board installation steps and check each one. All the
other test results are perfect. Got to be something in the synthesizer
circuits I have goofed up. Just gotta find it. Thanks again.

73,
Jim, K4ZMV

----- Original Message -----
From: "Don Wilhelm" <[hidden email]>
To: "Jim Brassell" <[hidden email]>; <[hidden email]>
Sent: Sunday, September 24, 2006 9:34 PM
Subject: RE: [Elecraft] VCO Alignment

> Jim,
>
> The most common source of problems with the PLL or VCO is a solder bridge
> on
> the thermistor board. There are other possible sources, but check there
> first. You can often get to the back of the thermistor board by removing
> the front panel and the control board.
>
> You intermittent display is most likely an unsoldered connection (or
> poorly
> soldered) - usually on the front panel itself.
>
> So check the soldering first, then re-check the soldering, and when that
> is
> done, check the soldering - that is the most common failure and misplaced
> components runs in second place. Bad components are way down the list.
>
> 73,
> Don W3FPR
>
>
>> -----Original Message-----
>>
>> I am building K2 #5731 and I have run into two problems. The
>> first, and most serious, is in VCO alignment. When moving L30,
>> the voltage at the left end of R30 does not change from 8.03vdc.
>> I have been through the entire range of L30, very carefully, with
>> no change. I pulled out T5 and rewound it. It is as nearly
>> perfect as I can get it. When I measure vdc on T5, I see
>> approximately 0.01vdc on 1 and 2 and 2.65 on 3 and 4. I checked
>> voltages on U4 and U6 and they are in the range of the table in
>> the back of the manual. I've checked all the components
>> installed and the soldering. This is my second K2 and I have
>> been a lot more careful. I'm stumped. Anybody got any ideas.
>>
>> The second thing is that parts of the mode indicator on the
>> display have become intermittent. Any ideas on that?
>>
>> Thanks.
>>
>> Jim, K4ZMV
>>
>
>

Hank Kryger

Re: VCO Alignment

In reply to this post by Jim K4ZMV

Hi
Had a similar problem. Building K2 5669, check U4 carefully, cold
solder joints etc. Check your Q in the center front of the board. I
am not at my hamshack but will look tomorrow which Q could be the
problem. In my case it was U4. good luck Hank WA9QJH

On 24, Sep 2006, at 19:49, Jim Brassell wrote:

> Hello.
>
> I am building K2 #5731 and I have run into two problems. The first,
> and most serious, is in VCO alignment. When moving L30, the voltage
> at the left end of R30 does not change from 8.03vdc. I have been
> through the entire range of L30, very carefully, with no change. I
> pulled out T5 and rewound it. It is as nearly perfect as I can get
> it. When I measure vdc on T5, I see approximately 0.01vdc on 1 and 2
> and 2.65 on 3 and 4. I checked voltages on U4 and U6 and they are in
> the range of the table in the back of the manual. I've checked all
> the components installed and the soldering. This is my second K2 and
> I have been a lot more careful. I'm stumped. Anybody got any ideas.
>
> The second thing is that parts of the mode indicator on the display
> have become intermittent. Any ideas on that?
>
> Thanks.
>
> Jim, K4ZMV
> _______________________________________________
> 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
>
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>
>