Dead K2

[Kristina Wright-3]

Hi all,
In building my K2 everything has gone perfectly and without a hitch  
until I got to the Alignment and Test, Part III. When I try to turn  
it on there's an audio "pop" but nothing on the LCD display and no  
relays clicking. It worked just fine before I installed the  
transmitter part. Its probably something simple, but I don't know  
what. Any ideas??

73,
Kristina, KE7LUC

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[Don Wilhelm-3]

Kristina,

It sounds like you have created a short in the DC power and the
resettable fuse is being activated.

Check all your soldering and the pad placement of the thermal pads for
the PA transistors.  Did you check for a short at the collectors of Q7
and Q8 as instructed?  If so, what was your resistance reading.

73,
Don W3FPR

Kristina Wright wrote:
> Hi all,
> In building my K2 everything has gone perfectly and without a hitch
> until I got to the Alignment and Test, Part III. When I try to turn it
> on there's an audio "pop" but nothing on the LCD display and no relays
> clicking. It worked just fine before I installed the transmitter part.
> Its probably something simple, but I don't know what. Any ideas??
>
> 73,
> Kristina, KE7LUC
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[Kristina Wright-3]

Nothing I can see looks to be shorted. And yes I checked the
collectors of Q7 and Q8 and it was 1.6 k ohms, so the problem doesn't
seem to be there. I'll go fiddle with it some more.

Kristina, KE7LUC

On 5/24/07, Don Wilhelm <[hidden email]> wrote:

> Kristina,
>
> It sounds like you have created a short in the DC power and the
> resettable fuse is being activated.
>
> Check all your soldering and the pad placement of the thermal pads for
> the PA transistors.  Did you check for a short at the collectors of Q7
> and Q8 as instructed?  If so, what was your resistance reading.
>
> 73,
> Don W3FPR

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[Kristina Wright-3]

OK, here's what I've done so far: checked the resistance from the
power plug to ground, the meter read infinite resistance. Also checked
the voltage at the same and got 12 volts. Then I measured the voltage
at the cathode end of D10 and got 12 volts with the power switch on
and off, but at D12 I got nothing with the power off and 0.7 volts
with it on. Obviously the fuse is being tripped, but I still don't see
any shorts (yes I inspected the whole board carefully).
  Thanks for the help so far, any more ideas?

73,
Kristina, KE7LUC


Jim, <[hidden email]> wrote:

Check the voltage at the power connector when it is dead and see if
you have 12 volts there.  Also check on the other side of the
resetable fuse on the right side of the rf board and make sure it is
not opening up.  A good place to check the voltage is at the cathode
end of the big power diode on the right side of the rf board.  and at
the pins of the on/off switch.

Jim K4ZM

------------------------------------------------------------------------------------------------------------
Don Wilhelm <[hidden email]> wrote:

> OK, check the resistance from the coaxial power plug to ground both with
> the switch on and with it off.  If you find the resistance at 500 ohms
> or more, then the K2 is likely OK, check your power supply and cord for
> good solid connections - you are using a proper regulated power supply
> rated at 3 amps or greater are you not?
>
> If all is OK there, measure the voltage at D10 cathode and D12 cathode
> (with the power turned on - of course).
>
> 73,
> Don W3FPR

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[Don Wilhelm-3]

Kristina,

You will just have to continue measuring things until you discover the
root cause.  Did you measure the resistance at the power plug with the
power switch ON?  Try the checks below (in order until you find the source).

Measure the resistance to ground from the cathode of D12.  You may find
it quite low (indicating a short).  Remove the control board and check
it again - if the resistance increases, look for the problem on the
control board.

If not on the control board, remove the heat sink and then recheck - if
things are OK with the heat sink removed, check the thermal pads.

If you still have not found it, the 'hunting' gets more difficult.  Use
the schematic to follow the path of the 12V voltage line - it starts at
the lower right corner of RF Board sheet 1, and goes to the regulators
on the control board, and various places on the RF Board (mostly on
sheet 4).  Check those paths thoroughly, even if it means removing some
components to see which side of the component the short is located.
Remember that the most likely cause is a solder bridge (connecting 2
points that should not connect together) so a VERY careful visual
inspection may reveal the problem source.

Work in an orderly manner - a short on a power line is difficult to find
because the PC traces seem to go everywhere and it is difficult to
isolate them - expect some frustration in the process.

73,
Don W3FPR

Kristina Wright wrote:

> OK, here's what I've done so far: checked the resistance from the
> power plug to ground, the meter read infinite resistance. Also checked
> the voltage at the same and got 12 volts. Then I measured the voltage
> at the cathode end of D10 and got 12 volts with the power switch on
> and off, but at D12 I got nothing with the power off and 0.7 volts
> with it on. Obviously the fuse is being tripped, but I still don't see
> any shorts (yes I inspected the whole board carefully).
>  Thanks for the help so far, any more ideas?
>
> 73,
> Kristina, KE7LUC

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[Kristina Wright-3]

Many thanks to all who replied to my question. What happened was that  
while I was putting T4 on, I overheated the 7-8 winding and it melted  
through the insulation of the 3-4 winding, therefore shorting it. So  
I just rewound it and it works!
Thanks again!

73,
Kristina  KE7LUC
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