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K3 died again

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Martin Sole-3

K3 died again

Hi,

My K3 is quite an early unit, S/N 298. Recently upgraded with new synths
KRX3A and KXV3, I also have a P3 connected to the radio. A while back it
failed with a shorted smd capacitor on the K3REF board causing loss of
TX bias voltage. Today it has lost both receive and transmit and I am
thinking it might be from the same module. Here's the situation.

Rig powers on and appears to work normally except soft noise from the
speaker, no band noise to speak of and no signals. P3 shows plenty of
signals, S9 plus on FT8 freqs but nothing heard other than soft noise.
Tuning works as signals move in the band scope. No sub receiver signals
either and no TX output. Have not checked transverter output but expect
to find nothing there.

P3 take off at IF output so everything is clearly working up to there.
DSP seems to be working as width and shift cause the expected changes in
audio. S meter reads dead zero, no movement.

About the only common point I can see is the K3REF board so it would
appear a second failure on this module. Since this is where I had to do
earlier work I wouldn't put it past being a user inflicted fault, but
that repair was a month or more ago.

Anyone care to have a guess or share thoughts?

Martin, HS0ZED

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Don Wilhelm

Re: K3 died again

Martin,

I recommend you email [hidden email] because the support folks
have handy access to the K3 techs if they are not able to diagnose the
problem themselves, and can best assist you with the analysis.

73,
Don W3FPR

On 11/12/2019 7:48 AM, Martin Sole wrote:

> Hi,
>
> My K3 is quite an early unit, S/N 298. Recently upgraded with new synths
> KRX3A and KXV3, I also have a P3 connected to the radio. A while back it
> failed with a shorted smd capacitor on the K3REF board causing loss of
> TX bias voltage. Today it has lost both receive and transmit and I am
> thinking it might be from the same module. Here's the situation.
>
> Rig powers on and appears to work normally except soft noise from the
> speaker, no band noise to speak of and no signals. P3 shows plenty of
> signals, S9 plus on FT8 freqs but nothing heard other than soft noise.
> Tuning works as signals move in the band scope. No sub receiver signals
> either and no TX output. Have not checked transverter output but expect
> to find nothing there.
>
> P3 take off at IF output so everything is clearly working up to there.
> DSP seems to be working as width and shift cause the expected changes in
> audio. S meter reads dead zero, no movement.
>
> About the only common point I can see is the K3REF board so it would
> appear a second failure on this module. Since this is where I had to do
> earlier work I wouldn't put it past being a user inflicted fault, but
> that repair was a month or more ago.
>
> Anyone care to have a guess or share thoughts?
>
> Martin, HS0ZED
>
> ______________________________________________________________
> 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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Martin Sole-3

Re: K3 died again and fixed

In reply to this post by Martin Sole-3

A few days ago I posted the below message but had not had time until
today to dig a little deeper. I took as my starting point the loss of
both receive and transmit as an indicator that the culprit would likely
be something common to both and given the lack of receiver noise whilst
the P3 panadaptor showed normal signals and band noise suggested it
would be after the first conversion.

This suggested something in the second LO as a likely possibility and
with the first intent being to measure the oscillator signals. I used my
SDRplay RSP1 with the Steve Andrews spectrum analyser software as this
was handy and is easy to use. BTW, this is a great tool if you have any
of the RSP devices. Going to the KREF3 board between the synthesisers
and probing the 49.380MHz reference showed a healthy signal close to
0dBm, as expected since the P3 confirmed tuning works, so I moved to the
output of U2 the divide by 6, hmm, nothing, nada, zilch. Worries of a
dead 74VHC175 with no replacement on hand was the first thought but
rapidly followed by my knowledge that this board had not so long ago
suffered a capacitor failure causing loss of the 7 volt transmit bias.

With the KREF3 on the bench a quick measure from the 5 volt line to
ground showed 82 ohms after L2, 87 ohms between L1 and L2 and about 91
before L1. Way too low for sure. There are 3 components here C7, C19 and
U1. Having had a 0.1uF fail on this board already I was ready to bet the
farm on either C7 or C19. C19 was the first to be removed and I hit pay
dirt right off, shoulda bought that lottery ticket today! Another dud
0.1uF then. Measuring the 5v to ground showed it now at a much more
respectable 1.3k ohms. Replacement was with a 1206 0.1 as I had done
earlier with C6.

Normal service is resumed. It's all back working as it should but I do
wonder now about the possible longevity of the other 0.1uF capacitors
both on this board and possibly in other parts of the radio. I count 12
more on this board alone.

I should mention that my K3 is an early unit, S/N 298 so I presume circa
2008-ish. More than 10 years is not bad in my book and the faults have
been fairly straight forward. It might be surface mount but it's
eminently repairable.

Martin, HS0ZED

On 12/11/2019 19:48, Martin Sole wrote:

> Hi,
>
> My K3 is quite an early unit, S/N 298. Recently upgraded with new
> synths KRX3A and KXV3, I also have a P3 connected to the radio. A
> while back it failed with a shorted smd capacitor on the K3REF board
> causing loss of TX bias voltage. Today it has lost both receive and
> transmit and I am thinking it might be from the same module. Here's
> the situation.
>
> Rig powers on and appears to work normally except soft noise from the
> speaker, no band noise to speak of and no signals. P3 shows plenty of
> signals, S9 plus on FT8 freqs but nothing heard other than soft noise.
> Tuning works as signals move in the band scope. No sub receiver
> signals either and no TX output. Have not checked transverter output
> but expect to find nothing there.
>
> P3 take off at IF output so everything is clearly working up to there.
> DSP seems to be working as width and shift cause the expected changes
> in audio. S meter reads dead zero, no movement.
>
> About the only common point I can see is the K3REF board so it would
> appear a second failure on this module. Since this is where I had to
> do earlier work I wouldn't put it past being a user inflicted fault,
> but that repair was a month or more ago.
>
> Anyone care to have a guess or share thoughts?
>
> Martin, HS0ZED

Earlier

Hi,

So I had some success in fixing this and thought I would write it up
here briefly for future reference.

Short version
C6 on the K3REF module had become a 12 ohm resistor.

Longer version
Finding the 7T line only going to 3.5 volts or so was suspicious.
Measuring the resistance to ground of that line showed about 20 ohms
where the 7 volts is generated at U11 on the RF board, very suspicious.
The first step then was to remove any removable item that has a
connection to the 7T line. That's most modules in the K3. Checking the
resistance of the 7T line each time I removed a plug in module showed
the fault to be somewhere on the K3REF module. The 7T line on this board
goes to Q3 via R16, R8 and R9 and also to Q2 and U3 via L5. Measuring
either side of L5 showed lower resistance on the Q2 and U3 side, now
around 12 ohms as opposed to 14 or so at pin 3 of P75. Focus then was
directed at Q2 and U3 as likely culprits being active devices likely
more prone to failure but removing Q2 showed no change nor did very
carefully lifting pin8 of U3 and confirming no connection to L5. That
left C6 as the remaining component on that line and its removal restored
a much healthier 2.7k resistance to ground on that line as formed by
R16, R8 and R9 around Q3 noted above.

I don't have any of the microscopic 0.1uF capacitors used in this
location, are they 0402? but I have a good selection of 1206 parts and
being smaller than the chokes on this board I considered it a suitable
change. The board mounts very close to the chassis so size is critical.

All restored and the rig is back to normal working order. I don't know
if these capacitors are prone generally to such failures but at least it
was on a plug in board so easy to narrow down.

So that was a fun Saturday afternoon for an hour or so, hopefully the
radio will keep on working well now.

Martin, HS0ZED
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Geoffrey Downs

Re: K3 died again and fixed

David Box-2

Re: K3 died again and fixed

In reply to this post by Martin Sole-3

If you are doing hand solder replacements of SMD capacitors you should
make sure you follow procedures to either pre-heat the component or take
extreme precautions to guarantee that the soldering iron does not touch
the capacitor electrodes. Thermal shock with cause the metal endcaps to
crack the ceramic which will eventually cause high leakage or shorts in
the capacitor.

Seeing that you have found two SMD caps on the same board have failed
then I am suspicious of the fabrication of this particular board.

You might want to reference
<www.kemet.com/Lists/TechnicalArticles/Attachments/49/F9207%20KEMET%20Hand%20Soldering%20Procedures.pdf>

There are other stresses that can cause the capacitor to crack and fail
such as board bending or contaminants under the part, BUT for home lab
work the primary reason is thermal shocking during hand solder.

de Dave K5MWR

On 11/14/2019 00:37, Martin Sole wrote:

> A few days ago I posted the below message but had not had time until
> today to dig a little deeper. I took as my starting point the loss of
> both receive and transmit as an indicator that the culprit would
> likely be something common to both and given the lack of receiver
> noise whilst the P3 panadaptor showed normal signals and band noise
> suggested it would be after the first conversion.
>
> This suggested something in the second LO as a likely possibility and
> with the first intent being to measure the oscillator signals. I used
> my SDRplay RSP1 with the Steve Andrews spectrum analyser software as
> this was handy and is easy to use. BTW, this is a great tool if you
> have any of the RSP devices. Going to the KREF3 board between the
> synthesisers and probing the 49.380MHz reference showed a healthy
> signal close to 0dBm, as expected since the P3 confirmed tuning works,
> so I moved to the output of U2 the divide by 6, hmm, nothing, nada,
> zilch. Worries of a dead 74VHC175 with no replacement on hand was the
> first thought but rapidly followed by my knowledge that this board had
> not so long ago suffered a capacitor failure causing loss of the 7
> volt transmit bias.
>
> With the KREF3 on the bench a quick measure from the 5 volt line to
> ground showed 82 ohms after L2, 87 ohms between L1 and L2 and about 91
> before L1. Way too low for sure. There are 3 components here C7, C19
> and U1. Having had a 0.1uF fail on this board already I was ready to
> bet the farm on either C7 or C19. C19 was the first to be removed and
> I hit pay dirt right off, shoulda bought that lottery ticket today!
> Another dud 0.1uF then. Measuring the 5v to ground showed it now at a
> much more respectable 1.3k ohms. Replacement was with a 1206 0.1 as I
> had done earlier with C6.
>
> Normal service is resumed. It's all back working as it should but I do
> wonder now about the possible longevity of the other 0.1uF capacitors
> both on this board and possibly in other parts of the radio. I count
> 12 more on this board alone.
>
> I should mention that my K3 is an early unit, S/N 298 so I presume
> circa 2008-ish. More than 10 years is not bad in my book and the
> faults have been fairly straight forward. It might be surface mount
> but it's eminently repairable.
>
>
> Martin, HS0ZED
>
>
> On 12/11/2019 19:48, Martin Sole wrote:
>> Hi,
>>
>> My K3 is quite an early unit, S/N 298. Recently upgraded with new
>> synths KRX3A and KXV3, I also have a P3 connected to the radio. A
>> while back it failed with a shorted smd capacitor on the K3REF board
>> causing loss of TX bias voltage. Today it has lost both receive and
>> transmit and I am thinking it might be from the same module. Here's
>> the situation.
>>
>> Rig powers on and appears to work normally except soft noise from the
>> speaker, no band noise to speak of and no signals. P3 shows plenty of
>> signals, S9 plus on FT8 freqs but nothing heard other than soft
>> noise. Tuning works as signals move in the band scope. No sub
>> receiver signals either and no TX output. Have not checked
>> transverter output but expect to find nothing there.
>>
>> P3 take off at IF output so everything is clearly working up to
>> there. DSP seems to be working as width and shift cause the expected
>> changes in audio. S meter reads dead zero, no movement.
>>
>> About the only common point I can see is the K3REF board so it would
>> appear a second failure on this module. Since this is where I had to
>> do earlier work I wouldn't put it past being a user inflicted fault,
>> but that repair was a month or more ago.
>>
>> Anyone care to have a guess or share thoughts?
>>
>> Martin, HS0ZED
>
> Earlier
>
>
> Hi,
>
> So I had some success in fixing this and thought I would write it up
> here briefly for future reference.
>
> Short version
> C6 on the K3REF module had become a 12 ohm resistor.
>
> Longer version
> Finding the 7T line only going to 3.5 volts or so was suspicious.
> Measuring the resistance to ground of that line showed about 20 ohms
> where the 7 volts is generated at U11 on the RF board, very
> suspicious. The first step then was to remove any removable item that
> has a connection to the 7T line. That's most modules in the K3.
> Checking the resistance of the 7T line each time I removed a plug in
> module showed the fault to be somewhere on the K3REF module. The 7T
> line on this board goes to Q3 via R16, R8 and R9 and also to Q2 and U3
> via L5. Measuring either side of L5 showed lower resistance on the Q2
> and U3 side, now around 12 ohms as opposed to 14 or so at pin 3 of
> P75. Focus then was directed at Q2 and U3 as likely culprits being
> active devices likely more prone to failure but removing Q2 showed no
> change nor did very carefully lifting pin8 of U3 and confirming no
> connection to L5. That left C6 as the remaining component on that line
> and its removal restored a much healthier 2.7k resistance to ground on
> that line as formed by R16, R8 and R9 around Q3 noted above.
>
> I don't have any of the microscopic 0.1uF capacitors used in this
> location, are they 0402? but I have a good selection of 1206 parts and
> being smaller than the chokes on this board I considered it a suitable
> change. The board mounts very close to the chassis so size is critical.
>
> All restored and the rig is back to normal working order. I don't know
> if these capacitors are prone generally to such failures but at least
> it was on a plug in board so easy to narrow down.
>
> So that was a fun Saturday afternoon for an hour or so, hopefully the
> radio will keep on working well now.
>
> Martin, HS0ZED
> ______________________________________________________________
> 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]