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Elecraft K3 problem

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LA7NO

Elecraft K3 problem

Hello,

The K3 suddenly stopped working.
One day all OK, the next day serious problems.

Serial no.: 07818.
It has ATU and 100 W PA installed, and also a P3 connected.
Both K3 and P3 were earlier well calibrated.
Supply: 14,5 VDC.

Symptoms:
- Rx seriously reduced sensitivity, only strong signals to be heard.
- No Tx output. Tuning not successful, no SWR indicated (only the 3
hyphens).
- Same on all bands.
- All displays, controls and menus apparently working normal.
- Mic-gain & ALC normal indication on SSB.

All menu settings seem to be OK.

Connected an XG3 and injected a -73 dBm signal.
It showed up on all bands with signal level about -100 dBm, so around 30 dB
attenuation.

Connected a LP-100A and a 50 ohm dummy load.
Whatever we tried, the LP-100A indicated zero power out on all bands.
Same on both Ant1 and Ant2.
Bypassed the ATU: no change.
Set power to < 10 W, effectively bypassing the PA: no change.

It is clearly something that is common for both Rx and Tx.
It is independent of the selected band.
Apparently not related to ATU or PA.

So, it could be some relay problem, or related to the SWR bridge or
LP-filters.

Hope you can give some helpful ideas on how to proceed.

Best regards & 73 from Norway,

Per-Tore / LA7NO

-----
73,

Per-Tore / LA7NO

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73,

Per-Tore / LA7NO

Wes Stewart-2

Re: Elecraft K3 problem

May be a LO problem. Check all of the TMP cables.

Wes N7WS

On 7/27/2020 5:50 AM, LA7NO wrote:

> Hello,
>
> The K3 suddenly stopped working.
> One day all OK, the next day serious problems.
>
> Serial no.: 07818.
> It has ATU and 100 W PA installed, and also a P3 connected.
> Both K3 and P3 were earlier well calibrated.
> Supply: 14,5 VDC.
>
> Symptoms:
> - Rx seriously reduced sensitivity, only strong signals to be heard.
> - No Tx output. Tuning not successful, no SWR indicated (only the 3
> hyphens).
> - Same on all bands.
> - All displays, controls and menus apparently working normal.
> - Mic-gain & ALC normal indication on SSB.
>
> All menu settings seem to be OK.
>
> Connected an XG3 and injected a -73 dBm signal.
> It showed up on all bands with signal level about -100 dBm, so around 30 dB
> attenuation.
>
> Connected a LP-100A and a 50 ohm dummy load.
> Whatever we tried, the LP-100A indicated zero power out on all bands.
> Same on both Ant1 and Ant2.
> Bypassed the ATU: no change.
> Set power to < 10 W, effectively bypassing the PA: no change.
>
> It is clearly something that is common for both Rx and Tx.
> It is independent of the selected band.
> Apparently not related to ATU or PA.
>
> So, it could be some relay problem, or related to the SWR bridge or
> LP-filters.
>
> Hope you can give some helpful ideas on how to proceed.
>
> Best regards & 73 from Norway,
>
> Per-Tore / LA7NO
>
>
>
>
> -----
> 73,
>
> Per-Tore / LA7NO
>
> --
> Sent from: http://elecraft.365791.n2.nabble.com/
> ______________________________________________________________
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John Simmons

Re: Elecraft K3 problem

In reply to this post by LA7NO

Did you check the antenna selection?

--
73,
-John NI0K
https://www.qrz.com/db/NI0K
LA7NO wrote on 7/27/2020 7:50 AM:

George Danner-2

Re: Elecraft K3 problem

In reply to this post by LA7NO

All Bands?
If receiving a strong station, is it on frequency?

73
George AI4VZ

-----Original Message-----
From: LA7NO
Sent: Monday, July 27, 2020 8:50 AM
To: [hidden email]
Subject: [Elecraft] Elecraft K3 problem

Hello,

The K3 suddenly stopped working.
One day all OK, the next day serious problems.

Serial no.: 07818.
It has ATU and 100 W PA installed, and also a P3 connected.
Both K3 and P3 were earlier well calibrated.
Supply: 14,5 VDC.

Symptoms:
- Rx seriously reduced sensitivity, only strong signals to be heard.
- No Tx output. Tuning not successful, no SWR indicated (only the 3
hyphens).
- Same on all bands.
- All displays, controls and menus apparently working normal.
- Mic-gain & ALC normal indication on SSB.

All menu settings seem to be OK.

Connected an XG3 and injected a -73 dBm signal.
It showed up on all bands with signal level about -100 dBm, so around 30 dB
attenuation.

Connected a LP-100A and a 50 ohm dummy load.
Whatever we tried, the LP-100A indicated zero power out on all bands.
Same on both Ant1 and Ant2.
Bypassed the ATU: no change.
Set power to < 10 W, effectively bypassing the PA: no change.

It is clearly something that is common for both Rx and Tx.
It is independent of the selected band.
Apparently not related to ATU or PA.

So, it could be some relay problem, or related to the SWR bridge or
LP-filters.

Hope you can give some helpful ideas on how to proceed.

Best regards & 73 from Norway,

Per-Tore / LA7NO

-----
73,

Per-Tore / LA7NO

--
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Mike K8CN

Re: Elecraft K3 problem

In reply to this post by LA7NO

You might check the PIN diode T/R switch. The high attenuation in RX mode
and no output power even when the 100 W PA is bypassed suggest that one or
more of the PIN diodes in the T/R switch have failed "open."

Mike, K8CN

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LA7NO

Re: Elecraft K3 problem

Thanks, Mike.

I guess this is the MA4P PIN diodes D26 & D27.
Is there an easy way to check those?

P-T

-----
73,

Per-Tore / LA7NO

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73,

Per-Tore / LA7NO

Martin Sole-3

Re: Elecraft K3 problem

In reply to this post by LA7NO

Hi,

What Serial number?

I have found on my own and a friends K3, both very low S/N around 300,
that the KREF3 board has been the culprit for this exact problem.
First check the all the TMP cables to and from the KREF3 board and the
synths. If all look good you should examine the K3REF board.

In both cases I have found 100nF (0.1uF) capacitors on this board to be
essentially a low DC resistance. Look in particular at the 5 volt line.
This supply affect IC6 the divide by 6 which provides both the second LO
for the receivers and one input to the mixer for the TXIF1. Measure the
resistance to ground from either side of L1 and L2 to figure out which
capacitor is likely the cause of the problem.

Please keep the list posted on what you find.

Martin, HS0ZED

On 27/7/63 19:50, LA7NO wrote:

Martin Sole-3

Re: Elecraft K3 problem

Apologies, I just saw the serial number 7818, quite a bit newer so
maybe not a failed capacitor, yet :)

Martin, H0ZED

On 27/7/63 23:32, Martin Sole wrote:

> Hi,
>
> What Serial number?
>
> I have found on my own and a friends K3, both very low S/N around 300,
> that the KREF3 board has been the culprit for this exact problem.
> First check the all the TMP cables to and from the KREF3 board and the
> synths. If all look good you should examine the K3REF board.
>
> In both cases I have found 100nF (0.1uF) capacitors on this board to
> be essentially a low DC resistance. Look in particular at the 5 volt
> line. This supply affect IC6 the divide by 6 which provides both the
> second LO for the receivers and one input to the mixer for the TXIF1.
> Measure the resistance to ground from either side of L1 and L2 to
> figure out which capacitor is likely the cause of the problem.
>
> Please keep the list posted on what you find.
>
> Martin, HS0ZED
>
>
>
> On 27/7/63 19:50, LA7NO wrote:
>> Hello,
>>
>> The K3 suddenly stopped working.
>> One day all OK, the next day serious problems.
>>
>> Serial no.: 07818.
>> It has ATU and 100 W PA installed, and also a P3 connected.
>> Both K3 and P3 were earlier well calibrated.
>> Supply: 14,5 VDC.
>>
>> Symptoms:
>> - Rx seriously reduced sensitivity, only strong signals to be heard.
>> - No Tx output. Tuning not successful, no SWR indicated (only the 3
>> hyphens).
>> - Same on all bands.
>> - All displays, controls and menus apparently working normal.
>> - Mic-gain & ALC normal indication on SSB.
>>
>> All menu settings seem to be OK.
>>
>> Connected an XG3 and injected a -73 dBm signal.
>> It showed up on all bands with signal level about -100 dBm, so around 30 dB
>> attenuation.
>>
>> Connected a LP-100A and a 50 ohm dummy load.
>> Whatever we tried, the LP-100A indicated zero power out on all bands.
>> Same on both Ant1 and Ant2.
>> Bypassed the ATU: no change.
>> Set power to < 10 W, effectively bypassing the PA: no change.
>>
>> It is clearly something that is common for both Rx and Tx.
>> It is independent of the selected band.
>> Apparently not related to ATU or PA.
>>
>> So, it could be some relay problem, or related to the SWR bridge or
>> LP-filters.
>>
>> Hope you can give some helpful ideas on how to proceed.
>>
>> Best regards & 73 from Norway,
>>
>> Per-Tore / LA7NO
>>
>>
>>
>>
>> -----
>> 73,
>>
>> Per-Tore / LA7NO
>>
>> --
>> Sent from:http://elecraft.365791.n2.nabble.com/
>> ______________________________________________________________
>> 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 [hidden email]
>

Mike K8CN

Re: Elecraft K3 problem

In reply to this post by LA7NO

Hi Per-Tore,

I don't know if there's an easy way to check the PIN diodes in the T/R
switch, especially since the SMD components of the switch are mostly on the
underside of the RF board. Here's where I would start:

1) Find spots on the RF board (top side) where you can measure the control
voltages 7R and 7T. Verify that these change in opposition to each other,
i.e. if 7R is high, 7T should be low and vice-versa, when changing from RX
mode to TX mode and back.

2) Presuming that both voltages 7R and 7T behave properly in switching from
RX to TX mode and back, I would measure the voltage on the drain of Q7, the
MOSFET switch, when 7R is high. Assertion of 7R should pull the Q7 drain
voltage low, which causes sufficient current to pass through both PIN diodes
D26 and D27 to enable the RX signal to pass through, presuming there is not
a problem with PIN diode D25.

3) It is possible that the Q7 drain voltage could be pulled low if only one
of PIN diodes D26 or D27 functions properly and the other has failed open,
so test (2) is not conclusive.

4) If you have a scope with a 10X probe, I would check for presence of RF on
the anode of PIN diode D43 when in TX mode - any frequency on the VFO within
the scope bandwidth should suffice. D43 must be forward-biased by the 7T
voltage in order for RF drive to be coupled to the low power (10 Watt) PA
assembly (Z2 on the block diagram). The fact that you have not been able to
detect any transmitted power in TX mode whether the 100 watt PA is bypassed
or not may indicate that the low power PA is not receiving drive from the
mixer. The 7T voltage is supplied to the anode of D43 via the low power PA
input connector, but it's unlikely that the simple path internal to the low
power PA board is at fault, i.e. 7T is not reaching D43.

I haven't had my K3 opened up for many years, nor have I experienced the
problem you described, so I can't easily point out where to access the
circuit points mentioned above.

There is another set of PIN diode switches around the mixer, but I would
start with those closest to the low power PA before going further back up
the signal processing chain.

73,
Mike, K8CN

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Mike K8CN

Re: Elecraft K3 problem

In reply to this post by Martin Sole-3

I agree with Martin's simpler hypothesis. The sudden change of behavior in
both TX and RX modes could well result from insufficient LO drive to either
the 1st or 2nd mixers. Check that possibility before launching into
detailed testing of the PIN diode T/R switch. It may be as simple as a
loose or corroded TMP connector.

Mike, K8CN

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Wes Stewart-2

Re: Elecraft K3 problem

I thought I said that.

On 7/27/2020 10:34 AM, Mike K8CN wrote:
> I agree with Martin's simpler hypothesis. The sudden change of behavior in
> both TX and RX modes could well result from insufficient LO drive to either
> the 1st or 2nd mixers. Check that possibility before launching into
> detailed testing of the PIN diode T/R switch. It may be as simple as a
> loose or corroded TMP connector.
>
> Mike, K8CN
>

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Mike K8CN

Re: Elecraft K3 problem

Aye, Wes, indeed you did! I wasn't thinking of LO drive levels when I first
read your post, but was thinking of common signal paths for TX and RX
through the T/R switch and no deeper into the signal processing chain.
Let's hope your and Martin's suggestion proves to be the true cause of
Per-Tore's issue.

Thanks, and 73,
Mike, K8CN

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Wes Stewart-2

Re: Elecraft K3 problem

I've had TMP connectors badly corroded in my K3. See:
https://groups.io/g/Elecraft-K3/album?id=37256

Wes N7WS

On 7/27/2020 12:04 PM, Mike K8CN wrote:
> Aye, Wes, indeed you did! I wasn't thinking of LO drive levels when I first
> read your post, but was thinking of common signal paths for TX and RX
> through the T/R switch and no deeper into the signal processing chain.
> Let's hope your and Martin's suggestion proves to be the true cause of
> Per-Tore's issue.
>
> Thanks, and 73,
> Mike, K8CN

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Don Wilhelm

Re: Elecraft K3 problem

That is why just looking for loose TMP connectors may not be sufficient.
While you are inside the K3, give all the TMP connectors a slight twist
which should clear some of the corrosion.

73,
Don W3FPR

On 7/27/2020 6:25 PM, Wes wrote:
> I've had TMP connectors badly corroded in my K3. See:
> https://groups.io/g/Elecraft-K3/album?id=37256
>
> Wes N7WS
>
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