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[K2] Lost 80m recieve.

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Alan Davenport

[K2] Lost 80m recieve.

Hello,

I have lost 80m receive on my K2 S/N:7012. I had this problem during the build but it "fixed itself" by the time I sorted out some other problems. 80m was working just fine for 6-7 months. The problem has returned.

Injecting a signal starting at the antenna, I get nothing on either side of K8, nothing if I inject at W1, and very weak signal if I inject at the output of relay K2. Strangely, it will TRANSMIT on 80m with normal power levels but it outputs a signal at approximately 3712 and that does not change when the VFO is changed. The VFO digits change as expected as the dial is rotated.

I re-soldered all connections for 80m from in the band pass and the low pass filters. I temporarily removed the ATU to remove that from the equation with no effect on the results.

It seems significant to me that it will transmit and that the transmit frequency is fixed at an incorrect value. Honestly though I am at a loss and need some advice as to how to proceed. Any help will be greatly appreciated.

73 de Al, W2GZN
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Don Wilhelm-4

Re: [K2] Lost 80m recieve.

Alan,

First of all, transmission at a fixed frequency of 3712 is indicative of
a problem with the VCO/PLL.
Are the R30 (VCO voltage) values within range on all bands? That is the
starting point.

Next put the internal probe into TP1 and measure the frequency when the
K2 is tuned to 3500, and also at 4000 kHz. The measured frequency
should be near 4913 kHz above the frequency shown on the K2 display.

If the frequency is not correct, the K2 will transmit on the wrong
frequency.

Give us the results from the above tests and we can proceed from there.

73,
Don W3FPR

On 9/5/2011 8:40 PM, Alan Davenport wrote:

> Hello,
>
> I have lost 80m receive on my K2 S/N:7012. I had this problem during the build but it "fixed itself" by the time I sorted out some other problems. 80m was working just fine for 6-7 months. The problem has returned.
>
> Injecting a signal starting at the antenna, I get nothing on either side of K8, nothing if I inject at W1, and very weak signal if I inject at the output of relay K2. Strangely, it will TRANSMIT on 80m with normal power levels but it outputs a signal at approximately 3712 and that does not change when the VFO is changed. The VFO digits change as expected as the dial is rotated.
>
> I re-soldered all connections for 80m from in the band pass and the low pass filters. I temporarily removed the ATU to remove that from the equation with no effect on the results.
>
> It seems significant to me that it will transmit and that the transmit frequency is fixed at an incorrect value. Honestly though I am at a loss and need some advice as to how to proceed. Any help will be greatly appreciated.
>
> 73 de Al, W2GZN
> ______________________________________________________________
> 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
>

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Don Wilhelm-4

Re: [K2] Lost 80m recieve.

In reply to this post by Alan Davenport

Alan,

Additional information:
The fact that it failed at one point earlier, and "fixed itself" for a
while strongly suggests a bad solder connection in the PLL/VCO area. It
works one time and not another is usually an intermittent solder
connection problem.

73,
Don W3FPR

On 9/5/2011 8:40 PM, Alan Davenport wrote:

Alan Davenport

Re: [K2] Lost 80m recieve.

In reply to this post by Don Wilhelm-4

Good Morning Don,

     Well it certainly looks like it is a VCO issue. On all bands except 80m, it is working correctly however on 80m here are the results:

3.5 MHz = 11038.61 MHz
4.0 MHz = 11038.51 MHz

Subtracting 4913 KHz gives me ~ 6125.6 KHz.

No wonder 80m isn't working. What surprises me is that this issue is confined to just one band. What is your suggestion on what to check?

    Thank you again Don,
     73 de Al, W2GZN

From: Don Wilhelm <[hidden email]>
To: Alan Davenport <[hidden email]>
Cc: "[hidden email]" <[hidden email]>
Sent: Monday, September 5, 2011 9:04 PM
Subject: Re: [Elecraft] [K2] Lost 80m recieve.

Alan,

First of all, transmission at a fixed frequency of 3712 is indicative of a problem with the VCO/PLL.
Are the R30 (VCO voltage) values within range on all bands? That is the starting point.

Next put the internal probe into TP1 and measure the frequency when the K2 is tuned to 3500, and also at 4000 kHz. The measured frequency should be near 4913 kHz above the frequency shown on the K2 display.

If the frequency is not correct, the K2 will transmit on the wrong frequency.

Give us the results from the above tests and we can proceed from there.

73,
Don W3FPR
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Don Wilhelm-4

Re: [K2] Lost 80m recieve.

Alan,

That sounds like you tuned down from 40 meters to the 80 meter band, and
the VFO could go no lower than 11038 MHz. If so, it is easy to fix -
just do a direct frequency entry to any frequency in the 80 meter band.

If that does not fix it, then check the soldering on RF Board C72.
Another possibility is a bad relay at K13, but if all other bands are
OK, then the relay is quite low on the suspect list - but check the
soldering at K13 pin 4 since that pin only switches in C72,

73,
Don W3FPR

On 9/6/2011 8:33 AM, Alan Davenport wrote:

> Good Morning Don,
>
> Well it certainly looks like it is a VCO issue. On all bands except 80m, it is working correctly however on 80m here are the results:
>
> 3.5 MHz = 11038.61 MHz
> 4.0 MHz = 11038.51 MHz
>
> Subtracting 4913 KHz gives me ~ 6125.6 KHz.
>
> No wonder 80m isn't working. What surprises me is that this issue is confined to just one band. What is your suggestion on what to check?
>
> Thank you again Don,
> 73 de Al, W2GZN
>
>
>

Alan Davenport

Re: [K2] Lost 80m recieve.

In reply to this post by Alan Davenport

I just performed the VCO voltage checks you asked for and here are the results. It looks like it was worse than I thought. 40,30,20 and 12 meteres are all within spec. The other bands are as follows:

3.5 MHz = no output
4.0 MHz = no output
18.0 = 7.94v
18.2 = 7.94v
21.0, 21.45, 28.0 and 28.8 are all also fixed at 7.94V.

I never noticed the other bands had gone dead as I operate mostly on 40m CW some operation on 20m and 30m. "When are the higher bands ever going to open up?" hihi

    73 de Al, W2GZN

From: Alan Davenport <[hidden email]>
To: "[hidden email]" <[hidden email]>
Cc: "[hidden email]" <[hidden email]>
Sent: Tuesday, September 6, 2011 8:33 AM
Subject: Re: [Elecraft] [K2] Lost 80m recieve.

Good Morning Don,

     Well it certainly looks like it is a VCO issue. On all bands except 80m, it is working correctly however on 80m here are the results:

3.5 MHz = 11038.61 MHz
4.0 MHz = 11038.51 MHz

Subtracting 4913 KHz gives me ~ 6125.6 KHz.

No wonder 80m isn't working. What surprises me is that this issue is confined to just one band. What is your suggestion on what to check?

    Thank you again Don,
     73 de Al, W2GZN
______________________________________________________________
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Help: http://mailman.qth.net/mmfaq.htm
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Don Wilhelm-4

Re: [K2] Lost 80m recieve.

Al,

With that new information, I can say that the problem is in the VFO
Range Selection area. It could be relay(s) or it could be capacitors.
Do you have soldering iron burned cases on any of K13, K14 or K15? If
so, those relays should be replaced since that is the most likely problem.

If the relay cases look good, then it is time to measure the relay
contacts with your ohmmeter. Use the schematic (RF Board sheet 2 to
determine the pins associated with the set and reset state of the relays
- they are shown in the reset state. Then switch to each band and
consult the chart at the upper left of the Schematic Key page to see
which of relays K13, K14 and K15 are set for that band. Confirm with
your ohmmeter that there is continuity between the correct pins of the
relay. Continue for other bands until you have confirmed that the
proper relays have been set, and also check that those which are
supposed to be reset are actually in that state.

It is also possible that you have a bad output from the I/O Controller
and the relay is not getting the pulse to set, but that is a rare
occurrence.

73,
Don W3FPR

On 9/6/2011 9:03 AM, Alan Davenport wrote:

> I just performed the VCO voltage checks you asked for and here are the results. It looks like it was worse than I thought. 40,30,20 and 12 meteres are all within spec. The other bands are as follows:
>
> 3.5 MHz = no output
> 4.0 MHz = no output
> 18.0 = 7.94v
> 18.2 = 7.94v
> 21.0, 21.45, 28.0 and 28.8 are all also fixed at 7.94V.
>
> I never noticed the other bands had gone dead as I operate mostly on 40m CW some operation on 20m and 30m. "When are the higher bands ever going to open up?" hihi
>
> 73 de Al, W2GZN
>
>

Don Wilhelm-4

Re: [K2] Lost 80m recieve.

In reply to this post by Alan Davenport

Al,

Just to add a little to the "sensibility" of the VCO (R30) voltage readings:
The range of voltages possible is from 0 to about 8 volts. Your high
voltage readings indicate that the PLL is trying to increase the voltage
to the varactors in order to reduce the capacity - and the op amp has
simply "run out of steam" and can go no higher. Voltages between 1.5
and 7 volts are workable, but outside that range, the varactors are not
linear.

A higher than normal voltage means there is excess capacity in the VFO
range select controls, and a low voltage means that there is not enough
capacity in the circuit.
Relays K13, K14, and K15 control which fixed capacitors are placed in
the circuit, and are in parallel with varactors D23 through D26.

On 9/6/2011 9:03 AM, Alan Davenport wrote:

Alan Davenport

Re: [K2] Lost 80m recieve.

In reply to this post by Don Wilhelm-4

Don,

    No, the relays are not damaged. I was extra careful with them as the build instructions said to be.

     I just re-flowed the solder on C72 and all K13 pins. The rig is now working on all bands and the VCO is in spec on all bands EXCEPT 80m. 80 was working briefly and just quit as I was typing my response. I switched bands and when I switched back to 80 it was dead again. Direct frequency entry does not help.

I think I had two seperate issues. 80M had been dead since I was away on vacation this June and the other bands were working fine. I do not know when they went dead but I do know I spent 7 weeks at a remote cabin and I used the K2 extensively on all bands up there. 80 went dead while I was there. (3 days after I put up a dipole to get on a net!)
.....

I just took it apart again, I reflowed the solder on all relays for 80m, K2,K3,K8,K13 and also K14 & K15 as well while I had it apart. 80m is currently working as are all other bands. I have switched bands many times and 80m continues to work. Looks like I may have fixed it with your help. As always Don, thank you very much for taking the time to help me and everyone else who asks for help.

    Take care,
Al, W2GZN
From: Don Wilhelm <[hidden email]>
To: Alan Davenport <[hidden email]>
Cc: "[hidden email]" <[hidden email]>
Sent: Tuesday, September 6, 2011 9:34 AM
Subject: Re: [Elecraft] [K2] Lost 80m recieve.

Al,

With that new information, I can say that the problem is in the VFO Range Selection area. It could be relay(s) or it could be capacitors. Do you have soldering iron burned cases on any of K13, K14 or K15? If so, those relays should be replaced since that is the most likely problem.

If the relay cases look good, then it is time to measure the relay contacts with your ohmmeter. Use the schematic (RF Board sheet 2 to determine the pins associated with the set and reset state of the relays - they are shown in the reset state. Then switch to each band and consult the chart at the upper left of the Schematic Key page to see which of relays K13, K14 and K15 are set for that band. Confirm with your ohmmeter that there is continuity between the correct pins of the relay. Continue for other bands until you have confirmed that the proper relays have been set, and also check that those which are supposed to be reset are actually in that state.

It is also possible that you have a bad output from the I/O Controller and the relay is not getting the pulse to set, but that is a rare occurrence.

73,
Don W3FPR
______________________________________________________________
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Don Wilhelm-4

Re: [K2] Lost 80m recieve.

Al,

Yes, the solder reflow should fix it. relay K15 must have a path to K14
before K13 is connected, and K13 then connects C72 for 80 meters - the
whole path must be intact.
Sounds like you got it.

73,
Don W3FPR

On 9/6/2011 11:16 AM, Alan Davenport wrote:

> Don,
>
> No, the relays are not damaged. I was extra careful with them as the build instructions said to be.
>
> I just re-flowed the solder on C72 and all K13 pins. The rig is now working on all bands and the VCO is in spec on all bands EXCEPT 80m. 80 was working briefly and just quit as I was typing my response. I switched bands and when I switched back to 80 it was dead again. Direct frequency entry does not help.
>
> I think I had two seperate issues. 80M had been dead since I was away on vacation this June and the other bands were working fine. I do not know when they went dead but I do know I spent 7 weeks at a remote cabin and I used the K2 extensively on all bands up there. 80 went dead while I was there. (3 days after I put up a dipole to get on a net!)
> .....
>
> I just took it apart again, I reflowed the solder on all relays for 80m, K2,K3,K8,K13 and also K14& K15 as well while I had it apart. 80m is currently working as are all other bands. I have switched bands many times and 80m continues to work. Looks like I may have fixed it with your help. As always Don, thank you very much for taking the time to help me and everyone else who asks for help.
>
> Take care,
> Al, W2GZN
>