K2 100 shuts down immediately - need help

[Stan AE7UT]

I have a K2/100 with a KAT100 that was running into a ZS6BKW.
On 15 meters it was showing "High Current" occasionally.  The rig
was turned on one morning and just immediately shut down with a
small amount of smoke coming from the rear of the rig.  Now the
rig will turnon, lights up and "Elecraft" show up and then it immediately
shuts down.

I opened the rig and could not see any apparent damage.  One of the PAs
has a "short" to ground of about 6 ohms.  I'm guessing that PA is dead.
I could be way off on that.

I called Elecraft - left a message - but have not heard back from them.
Any help would be much appreciated.

73
Stan AE7UT

[Don Wilhelm-4]

Stan,

It is getting late on Friday, and I would bet that Elecraft is flooded
with calls.  Perhaps I can help.
Was that measurement on the "PA transistor" in the KPA100 or the base K2
(collector of Q7 or Q8)?

Regardless of the answer to that, physically remove the KPA100 and power
the base K2 from the 2.1mm coaxial jack - connect a dummy load to the
ANT jack on the lower rear panel.
Does the base K2 have power output?  My guess is that it does not. With
Q7 and/or Q8 shorted, you will get the same shutdown situation.
If so, order the K2PAKIT from Elecraft and replace Q11 and Q13 first,
then with Q7 and Q8 removed, do a TUNE and check the voltage on the
solder pads for the base of Q7 and Q8 - if it is 0.60 to 0.64 volts, all
is well, proceed to install Q7 and Q8.  Then again test the base K2 for
proper power output and power control.

Once the base K2 is working, then remove the shield from the KPA100 and
examine it for anything that might look burned, especially the 1k
resistor across RFC3.  Check diodes D16 and D17 with your DMM. Also
check diodes D11, D12, D13 and D14 with your DMM.  Replace as
necessary.  If your KPA100 is not up to date (blue toroids at RFC1 and
L16) this is a good time to update it with KPA100UPKT.  If your shield
is not up to date - clips to the K2 side panels, narrow notch at the
SO-239 jack location and solder lugs to connect the outside of the
shield to the SO-239 (and the speaker magnet shield), now is a good time
to do the updated shield as well.

The reason for all those checks is that what normally happens is a
static surge coming in on the antenna feedline will damage D16 and/or
D17 in the KPA100 wattmeter.  Once that happens, there will be a loss of
power control, and the power output will always be at max power (which
may be in excess of 180 watts).  In time, if that condition is not
noticed and corrected, the PA transistors have been putting out "their
all" trying to provide drive, and will fail. base K2 Q11 and Q13 are
often damaged as a secondary failure.

The other possible failure scenario is that something in the KPA100 T/R
switch failed and caused the other failures.  If you have the updated
KPA100, that is a rare occurrence, but if your KPA100 is back-level, it
can happen without warning, particularly while tuning with the KAT100 on
40 meters - a parasitic can develop that can cause damage to the KPA100
T/R switch.

So now you have the full story, and you should be able to determine
which components may have failed.

73,
Don W3FPR


On 8/9/2013 5:42 PM, Stan AE7UT wrote:

> I have a K2/100 with a KAT100 that was running into a ZS6BKW.
> On 15 meters it was showing "High Current" occasionally.  The rig
> was turned on one morning and just immediately shut down with a
> small amount of smoke coming from the rear of the rig.  Now the
> rig will turnon, lights up and "Elecraft" show up and then it immediately
> shuts down.
>
> I opened the rig and could not see any apparent damage.  One of the PAs
> has a "short" to ground of about 6 ohms.  I'm guessing that PA is dead.
> I could be way off on that.
>
> I called Elecraft - left a message - but have not heard back from them.
> Any help would be much appreciated.
>
> 73
> Stan AE7UT
>
>
>
> --
> View this message in context: http://elecraft.365791.n2.nabble.com/K2-100-shuts-down-immediately-need-help-tp7577571.html
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[Stan AE7UT]

Thanks Don.
I'll order the kit on Monday.
I did take off the KPA100 to do the testing.
The short is from the collector of Q7.
No output of course because it only remains on for about a second.

I'll let you know how it works out.

73
Stan AE7UT

[Stan AE7UT]

The transistors arrived yesterday and I did ALL Don advised.
Everything checked out and I replaced the transistors with amazing ease.
All the diodes appeared healthy and the voltage was spot on.
Start to finish and being very careful, it took about 4 hours.
I'm getting 100 watts out and all is well in Zion.

I'm still getting a "High Current" warning occasionally at the first bit of transmission.
Is this common/normal and should I check something else?

Interestingly this is serial number #7230 but from what Don was saying it
appears to have an older amp on it.  I still haven't built a KPA100 so I'm
not very familiar with them but it does have a shield on it as Don described.
How important is that fix?  

Elecraft has once again endeared themselves to me.  
I have very little electronics back ground.  To be able to open a rig and fix
it is really cool.   This would have been unthinkable without the help of this group.  

I want to give a special THANKS to Don W3FPR, Dale WC7S and Dick K2ZR.  

73
Stan AE7UT

[Don Wilhelm-4]

Stan,

First check the menu CAL CUR setting.  It should be set at 3.50 - if it
is lower, that would explain the HiCur messages.

Check your power supply voltage.  It should be 13.8 volts or higher (up
to 14.5 volts).  The K2 tries to maintain the requested power output,
and if the voltage is low, it will draw more current to produce the
requested power.

If CAL CUR is OK, then try to determine if it occurs only on certain
bands - do not set the power control fully clockwise for one thing, keep
it at 100 watts (or below) - do you still get the HiCur messages? - if
not, all is well.
It is not unusual to get an occasional HiCur warning on 160 or 80 meters
when the power knob is fully clockwise.

If you get HiCur messages on all bands, take a look at transformer T4.  
It should have 3 turns of white wire on the secondary winding. If it has
only 2 turns, someone built it for "better efficiency at 5 watts", which
should only be used with a K2 that will only be used on CW at power
levels less than 5 watts.  It should not be used if either the KSB2 or
the KPA100 options are installed.

If you get HiCur warnings only on selected bands (40m, 20m, 15m, and
10m), check the number of turns on the toroids of the Low Pass Filter in
the base K2 - builders sometimes put an extra turn on the cores which
will cause that problem.  If the bands are 30m, 17m and 10 meters, the
toroid turns on the KPA100 LPF may have an extra turn.

If the KPA100 has two red core toroids near the center of the board, it
is the older design.  The new one has blue core toroids at RFC1 and L16
locations.

So that is as much as I can tell you with the information I have.

73,
Don W3FPR

On 8/17/2013 12:11 PM, Stan AE7UT wrote:

> The transistors arrived yesterday and I did ALL Don advised.
> Everything checked out and I replaced the transistors with amazing ease.
> All the diodes appeared healthy and the voltage was spot on.
> Start to finish and being very careful, it took about 4 hours.
> I'm getting 100 watts out and all is well in Zion.
>
> I'm still getting a "High Current" warning occasionally at the first bit of
> transmission.
> Is this common/normal and should I check something else?
>
> Interestingly this is serial number #7230 but from what Don was saying it
> appears to have an older amp on it.  I still haven't built a KPA100 so I'm
> not very familiar with them but it does have a shield on it as Don
> described.
> How important is that fix?
>
> Elecraft has once again endeared themselves to me.
> I have very little electronics back ground.  To be able to open a rig and
> fix
> it is really cool.   This would have been unthinkable without the help of
> this group.
>
> I want to give a special THANKS to Don W3FPR, Dale WC7S and Dick K2ZR.
>
> 73
> Stan AE7UT
>

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