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K2 Won't power on

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JeremyJones

K2 Won't power on

So my K2, which has been running great for almost a year, no longer powers on. I had left it powered on and connected via the serial cable to a computer so that I could do PSK-31 contacts remotely while I was away from home. Unfortunately I never got the chance, and upon my return home, my K2 was no longer working (no lights or any indication of life). I shut it off for a couple of hours, and upon turning it back on, I got a loud buzz, then everything shut down again. There was no lightning or power outages while I was gone, and unless the computer somehow put the radio into transmit, it should only have been receiving. Any ideas on where I should start to look to trouble shoot this?

Thanks for any help,
Jeremy
VA3ZTF

daleputnam

Re: K2 Won't power on

Hi Jeremy, That has the possibility of being the finals... where a bit of static, wind maybe? depending on the antenna connected, may have poked the finals too hard. A quick check would be to use an ohm meter, before replacement.

Have a great day,

--... ...--
Dale - WC7S in Wy

> Date: Tue, 11 Feb 2014 16:44:25 -0800
> From: [hidden email]
> To: [hidden email]
> Subject: [Elecraft] K2 Won't power on
>
> So my K2, which has been running great for almost a year, no longer powers
> on. I had left it powered on and connected via the serial cable to a
> computer so that I could do PSK-31 contacts remotely while I was away from
> home. Unfortunately I never got the chance, and upon my return home, my K2
> was no longer working (no lights or any indication of life). I shut it off
> for a couple of hours, and upon turning it back on, I got a loud buzz, then
> everything shut down again. There was no lightning or power outages while I
> was gone, and unless the computer somehow put the radio into transmit, it
> should only have been receiving. Any ideas on where I should start to look
> to trouble shoot this?
>
> Thanks for any help,
> Jeremy
> VA3ZTF
>
>
>
> --
> View this message in context: http://elecraft.365791.n2.nabble.com/K2-Won-t-power-on-tp7584083.html
> Sent from the Elecraft mailing list archive at Nabble.com.
> ______________________________________________________________
> Elecraft mailing list
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> Post: mailto:[hidden email]
>
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Don Wilhelm-4

Re: K2 Won't power on

In reply to this post by JeremyJones

Jeremy,

I can't recall a "loud buzz" condition, but I would suspect the PA
transistors in the base K2.
First, check the resistance from the collectors of Q7 and Q8 to ground.
If it is quite low, the PA transistors are toast - get the K2PAKIT and
install Q7, Q8 as well as Q11 and Q13.

If the K2 will not power up, you could remove T3 (easier than removing
Q7 and Q8) and see if it powers on.

The fact that it powers down usually indicates that too much current is
being drawn - the resettable fuse in the K2 trips at 5 amps.

I would suggest removing T3 and then making some measurements. Find out
if the 8R and 8T signals are behaving properly as a first step. If 8T is
present at the same time as 8R, that says the K2 is trying to transmit
at the same time it is receiving.

Try isolating the DC to Q7 and Q8 (by removing T3) and then we can help
you debug things after you get it to power up.

73,
Don W3FPR

On 2/11/2014 7:44 PM, JeremyJones wrote:

> So my K2, which has been running great for almost a year, no longer powers
> on. I had left it powered on and connected via the serial cable to a
> computer so that I could do PSK-31 contacts remotely while I was away from
> home. Unfortunately I never got the chance, and upon my return home, my K2
> was no longer working (no lights or any indication of life). I shut it off
> for a couple of hours, and upon turning it back on, I got a loud buzz, then
> everything shut down again. There was no lightning or power outages while I
> was gone, and unless the computer somehow put the radio into transmit, it
> should only have been receiving. Any ideas on where I should start to look
> to trouble shoot this?
>
> Thanks for any help,
> Jeremy
> VA3ZTF
>

JeremyJones

Re: K2 Won't power on

Q7 and Q8 both read 12.3 ohms from collector to ground.

The symptoms definitely resemble blown finals, as I experienced the same thing when I was building the kit, including the over current tripping the resettable fuse. I just didn't expect that from a receive only condition.

Jeremy
VA3ZTF

daleputnam

Re: K2 Won't power on

Depending on the antenna you are using Jeremy, it may be very very sensitive to static.IF your antenna has a dc (rf choke) to a good dc ground, that is also tied to the house power ground,the sensitivity will be lessened a lot. Without that.. a lightening strike 30 miles away can pop the finals... or a wind derived static, from a 25pmh breeze on a dipole. (voice of experience here) And.. I keep a complete set of the final replacement kit on hand all the time.

Have a great day,

--... ...--
Dale - WC7S in Wy

> Date: Tue, 11 Feb 2014 17:47:06 -0800
> From: [hidden email]
> To: [hidden email]
> Subject: Re: [Elecraft] K2 Won't power on
>
> Q7 and Q8 both read 12.3 ohms from collector to ground.
>
> The symptoms definitely resemble blown finals, as I experienced the same
> thing when I was building the kit, including the over current tripping the
> resettable fuse. I just didn't expect that from a receive only condition.
>
> Jeremy
> VA3ZTF
>
>
>
>
> --
> View this message in context: http://elecraft.365791.n2.nabble.com/K2-Won-t-power-on-tp7584083p7584087.html
> Sent from the Elecraft mailing list archive at 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

Don Wilhelm-4

Re: K2 Won't power on

In reply to this post by JeremyJones

Jeremy,

OK, Q7 and Q8 are 'toast', you might as well remove them.

With Q7 and Q8 removed, do a TUNE and measure the DC voltage at the
solder pads for the base of Q7 and Q8. The expected voltage is 0.60 to
0.64 volts. If it is out of that range, replace Q11 and Q13 too. Those
transistors come included in the K2PAKIT.

73,
Don W3FPR

On 2/11/2014 8:47 PM, JeremyJones wrote:
> Q7 and Q8 both read 12.3 ohms from collector to ground.
>
> The symptoms definitely resemble blown finals, as I experienced the same
> thing when I was building the kit, including the over current tripping the
> resettable fuse. I just didn't expect that from a receive only condition.
>
> Jeremy
> VA3ZTF
>

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Don Wilhelm-4

Re: K2 Won't power on

In reply to this post by JeremyJones

Jeremy,

One afterthought -- although Q7 and Q8 are the top suspects for your
problem, after removing them, check the resistance from the Q7/Q8
collector solder pads to ground. If it is still low, the problem is
something other than Q7 and Q8.

73,
Don W3FPR

-------------------------------------------

Jeremy,

OK, Q7 and Q8 are 'toast', you might as well remove them.

With Q7 and Q8 removed, do a TUNE and measure the DC voltage at the
solder pads for the base of Q7 and Q8. The expected voltage is 0.60 to
0.64 volts. If it is out of that range, replace Q11 and Q13 too. Those
transistors come included in the K2PAKIT.

73,
Don W3FPR

On 2/11/2014 8:47 PM, JeremyJones wrote:
> Q7 and Q8 both read 12.3 ohms from collector to ground.
>
> The symptoms definitely resemble blown finals, as I experienced the same
> thing when I was building the kit, including the over current tripping the
> resettable fuse. I just didn't expect that from a receive only condition.
>
> Jeremy
> VA3ZTF
>

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JeremyJones

Re: K2 Won't power on

With Q7/Q8 removed, the resistance from the Collector solder pad to ground on both is 70 ohms.

Doing a "Tune" with Q7/Q8 removed results in 1.0V on the Base pads and a Low P on the display. I do have the KAT2 installed, just in case this makes a difference. This was done into a dummy load.

The antenna that I normally run is an 80m Carolina Windom strung up between a tree in my front yard to a tree in my backyard. I have no additional grounding to it, just the baluns that are part of the normal antenna design. I am very cautious of lightning in the summer, and leave the antennas disconnected when not using the radio, however given that its winter here and sub zero temperatures, I didn't worry about it. I had never heard of static caused by the wind. What is a good way to protect against this?

Thanks,
Jeremy
VA3ZTF

Don Wilhelm-4

Re: K2 Won't power on

Jeremy,

70 ohms is too low on the +12 volt power line, you should see a large
capacitor charging and the resistance should climb if all is normal.
1 volt on the base during a TUNE is too high, so plan to replace Q11 and
Q13 - they are included in the K2PAKIT.

Yes, static can be induced by wind, rain and snow as well as nearby
lightning - we sometimes have lightning even in Winter.

Unfortunately, you will have to find where the problem origin is. You
can lift one end of R45 to remove Q5. Check again at the collector pad
for Q7 or Q8 after removing Q5.
Then to remove Q6, lift one end of RFC4 and check again.

To remove the RF Preamp from the 12 volt rail, lift one end of R74.
Check again.
To remove the Post Mixer Amp, lift one end of R82 and check once more.
To remove the TX Buffer, lift one end of R97 and check again.

If the 12 volt rail still shows low resistance to ground, you probably
have a faulty capacitor. Those are difficult to locate - it is probably
an electrolytic, so look for any that are not flat on the top. They
normally expand inside when they fail, so you are looking for a slightly
rounded top. Removal of all the capacitors on the 12 volt rail is the
next step if you cannot spot a bad one visually. Look at the schematic
and look for every line marked "+12v" - if there is a capacitor
connected to that line, remove it and check the resistance on the board
after each one.

Yes, a low resistance to ground is a nasty problem to troubleshoot and
just takes time to isolate to the failure. Work methodically - if you
jump around and try to "shotgun" it, the normal result is frustration.

73,
Don W3FPR

On 2/12/2014 8:58 AM, JeremyJones wrote:

> With Q7/Q8 removed, the resistance from the Collector solder pad to ground on
> both is 70 ohms.
>
> Doing a "Tune" with Q7/Q8 removed results in 1.0V on the Base pads and a Low
> P on the display. I do have the KAT2 installed, just in case this makes a
> difference. This was done into a dummy load.
>
> The antenna that I normally run is an 80m Carolina Windom strung up between
> a tree in my front yard to a tree in my backyard. I have no additional
> grounding to it, just the baluns that are part of the normal antenna design.
> I am very cautious of lightning in the summer, and leave the antennas
> disconnected when not using the radio, however given that its winter here
> and sub zero temperatures, I didn't worry about it. I had never heard of
> static caused by the wind. What is a good way to protect against this?
>
>

JeremyJones

Re: K2 Won't power on

Lifting one end of R45 still showed 70 ohms. Lifting one end of RFC4 increased to 87 ohms. I left the leg of R45 disconnected when taking this measurement, and I want to confirm whether I should leave the components disconnected as I go through, or reconnect them before moving on to the next.

Thanks,
Jeremy
VA3ZTF

Don Wilhelm-4

Re: K2 Won't power on

Jeremy,

Leave them disconnected until you find the culprit.
Take notes of waht you have done if necessary so you can restore things
after you have found the problem.

73,
Don W3FPR

On 2/12/2014 8:46 PM, JeremyJones wrote:
> Lifting one end of R45 still showed 70 ohms. Lifting one end of RFC4
> increased to 87 ohms. I left the leg of R45 disconnected when taking this
> measurement, and I want to confirm whether I should leave the components
> disconnected as I go through, or reconnect them before moving on to the
> next.
>
>

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JeremyJones

Re: K2 Won't power on

I have lifted R45, RFC4, R74, R82 and R97, with only a slight increase from 70 ohms to 87 ohms after lifting RFC4. I'll continue troubleshooting tomorrow by removing any capacitors connected to 12V.

I also want to confirm that I should be doing these resistance checks with no power applied.
Also, I am using an inexpensive ohm meter. Will that have enough power to charge the capacitors up enough to show the expected resistance?

Thanks,
Jeremy
VA3ZTF

Don Wilhelm-4

Re: K2 Won't power on

Jeremy,

Yes, you should be doing the resistance checks with no power applied.
Inexpensive ohmmeter? Well, if it is a digital multimeter in resistance
mode, you should be OK, but i it is an analog VOM or VTVM, it may not be
showing you the real picture because the voltage may be sufficient to
turn on semiconductor junctions.

73,
Don W3FPR

On 2/12/2014 9:15 PM, JeremyJones wrote:

> I have lifted R45, RFC4, R74, R82 and R97, with only a slight increase from
> 70 ohms to 87 ohms after lifting RFC4. I'll continue troubleshooting
> tomorrow by removing any capacitors connected to 12V.
>
> I also want to confirm that I should be doing these resistance checks with
> no power applied.
> Also, I am using an inexpensive ohm meter. Will that have enough power to
> charge the capacitors up enough to show the expected resistance?
>
> Thanks,
> Jeremy
> VA3ZTF
>
>
>
> --
> View this message in context: http://elecraft.365791.n2.nabble.com/K2-Won-t-power-on-tp7584083p7584157.html
> Sent from the Elecraft mailing list archive at Nabble.com.
> ______________________________________________________________
> Elecraft mailing list
> Home: http://mailman.qth.net/mailman/listinfo/elecraft
> Help: http://mailman.qth.net/mmfaq.htm
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>
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JeremyJones

Re: K2 Won't power on

Yes it is a digital multimeter, but I only paid about $10 for it.

What resistance should I be seeing. I have noticed some drastic variations as I change the scale on my meter. The 200 ohm scale gives a reading of 91 ohms
2000 ohms scale reads 1500
20K scale reads 3.7
200k scale reads 10.7

What other symptoms might I look for to check for an issue in the power rail.

I'm not sure if setting the scale to within the expected range will provide a useful reading or not. I think I'll borrow on of the Fluke meters from work this weekend.

Don Wilhelm-4

Re: K2 Won't power on

Jeremy,

I would tend to believe the reading on the 2000 ohm scale.
Look at the display in the 200 ohm scale and see if it shows a "+" to
the left - If so, that indicates overrange and you should switch to a
higher range.
I would also believe that the 20k and 200k scales are showing you
resistance in kilo ohms.
The voltage used for resistance measurements may change as you switch
scales.

In other words, it sounds like no short on the 12v power rail, but do
check the instructions for your meter so you know what the display is
telling you.

Inexpensive meters are normally fairly accurate for voltage readings,
but not necessarily for resistance.

73,
Don W3FPR

On 2/13/2014 1:55 PM, JeremyJones wrote:

> Yes it is a digital multimeter, but I only paid about $10 for it.
>
> What resistance should I be seeing. I have noticed some drastic variations
> as I change the scale on my meter. The 200 ohm scale gives a reading of 91
> ohms
> 2000 ohms scale reads 1500
> 20K scale reads 3.7
> 200k scale reads 10.7
>
> What other symptoms might I look for to check for an issue in the power
> rail.
>
> I'm not sure if setting the scale to within the expected range will provide
> a useful reading or not. I think I'll borrow on of the Fluke meters from
> work this weekend.
>
>
>
> --
> View this message in context: http://elecraft.365791.n2.nabble.com/K2-Won-t-power-on-tp7584083p7584195.html
> Sent from the Elecraft mailing list archive at Nabble.com.
> ______________________________________________________________
> Elecraft mailing list
> Home: http://mailman.qth.net/mailman/listinfo/elecraft
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>
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> Please help support this email list: http://www.qsl.net/donate.html
>

JeremyJones

Re: K2 Won't power on

There is no indication on the cheap meter for an out of scale reading.

I've borrowed a Fluke meter from work, and after watching the capacitors charge up, the resistance reading is 2.7k ohm. This is will all of the resistors still connected as above. I'll reconnect them one by one and check the readings to ensure there is no issue.

PA parts are on order and should be here next week I hope.

JeremyJones

Re: K2 Won't power on

So after reassembling everything minus Q7/8, resistance from ground to collector pad for Q7/8 starts at 600k ohm then gradually drops down to 54k ohm before reseting and spiking back up to 600k and dropping again. I believe this would be a capacitor charging up and then biasing a transistor?

Don Wilhelm-4

Re: K2 Won't power on

Jeremy,

From those resistance readings, I would say you are OK.
If you have all except Q7 and Q8 installed, do a TUNE and re-check the
voltage on the base solder pads of Q7 or Q8. If you do not see a
voltage between 6.2 and 6.4 volts, replace Q11 and Q13 and retest before
you install Q7 and Q8. You don't want to destroy new PA transistors
with too much base voltage.

You can make measurements without the heatsink when Q7 and Q8 are
removed, but once Q7 and Q8 are mounted, you must have the heatsink
installed if the PA transistors are expected to last longer than 30 seconds!

73,
Don W3FPR

On 2/14/2014 12:04 PM, JeremyJones wrote:
> So after reassembling everything minus Q7/8, resistance from ground to
> collector pad for Q7/8 starts at 600k ohm then gradually drops down to 54k
> ohm before reseting and spiking back up to 600k and dropping again. I
> believe this would be a capacitor charging up and then biasing a transistor?
>
>

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JeremyJones

Re: K2 Won't power on

I'm still getting 600mV and LowP during the tune, so it looks like I'll be replacing Q11 and Q13 as well.

Don Wilhelm-4

Re: K2 Won't power on

Jeremy,

Remove the tuner and you will not be bothered with the LowP messages.
In fact when testing the base K2, you should remove the tuner and
operate the basic K2 into a dummy load.

Where are you measuring 600mV? That is one problem with replying using
Nabble, it strips off what you are relying to and only Nabble users can
make sense of things. I choose to download directly from the Elecraft
list as email, so some hint of the history is helpful.

73,
Don W3FPR

On 2/16/2014 4:05 PM, JeremyJones wrote:

> I'm still getting 600mV and LowP during the tune, so it looks like I'll be
> replacing Q11 and Q13 as well.
>
>
>
> --
> View this message in context: http://elecraft.365791.n2.nabble.com/K2-Won-t-power-on-tp7584083p7584328.html
> Sent from the Elecraft mailing list archive at Nabble.com.
> ______________________________________________________________
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