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K2 DOA at second power up test

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ke4d

K2 DOA at second power up test

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Don Wilhelm-4

Re: K2 DOA at second power up test

John,

Either remove T3 or remove the PA transistors and see if it comes back
to life.
If it does, then replace the PA transistors. A dropped wire that
happens to short between the collector and the base of the PA
transistors will take them out in a microsecond!

73,
Don W3FPR

On 11/7/2011 4:54 PM, ke4d wrote:

> Ok, I've done a lot of dumb things in 37 years of amateur radio but when
> constructing my second K2 a few weeks ago, I dropped a piece of component
> wire on the RF board while doing the second power up test on the receiver.
> Bam, no power at all, no lights, no relays nada. I thought I blew D10 on
> the RF board but Elecraft tells me it leaks anyway. I changed it
> nonetheless, no joy. I get 12 volts on the main bus on the RF board until I
> hit the power switch. Then the voltage drops to 2.5 or so. I lifted the 5
> and 8 volt regulator output leads, still low voltage there. Changed them
> also but still no joy. I'm at a loss where to look next. I cannot find
> anything that warms up, looks bad, measures the wrong resistance, just low
> voltage. Low enough that the relays don't activate and the display is a
> dismal green with no power to it. Any suggestions other than buying another
> Icom or Kenwood? I could say the rig is KOA instead of DOA since I killed
> it!
>
> John KE4D
>
> --
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ke4d

Re: K2 DOA at second power up test

Thanks Don, Elecraft told me the same thing. However, as I told them, I'm on the second power up test in the manual, there is no T3 or PA transistor in on the board at this time. I've built the front panel, the control board and the receiver, no transmitter yet. I'm pretty sure its something in the 12v line, I just can't find it. I wondered about F1 but I show 12 volts on both sides of it so I guess its ok. And the power supply is fine, I have 12 volts on the RF board until I push the on switch on my front panel. Then the voltage drops to about 2.5. I figure something is pulling it down, I just need to find it! Thats what I get for building when I have to have my magnifying glasses on the see anything on those boards!

Don Wilhelm-4

Re: K2 DOA at second power up test

Sorry for my oversight - It did hit me that you only had the receiver
section built.

Can you follow on the schematic? I doubt the fuse is faulty - it is
probably working just fine and opens because there is more than 5 amps
of current - it does act rather fast.

Can you follow along in the schematic? chasing the source down will be
easier and make more sense if you can.
I suggest you measure the resistance of the 12 volt line - it will
probably be close to zero.
Then start lifting one end of selected components to isolate each stage
that uses 12 volts. Stop when the resistance on the 12 volt line goes
up - you have found the troublesome stage.
I would start with lifting one end of RFC11 (that is the toroid on the
bottom) to remove the Post-Mixer Amp.
Then lift one end of R74 to remove the Preamp.
Then lift one end of R97 to remove the TX Buffer.
The last component is regulator U2 which feeds the IO Controller.

That should be all the stages that you have built at this point which
draw directly on the 12 volt line (other than the regulators on the
Control Board.

73,
Don W3FPR

On 11/7/2011 5:53 PM, ke4d wrote:

> Thanks Don, Elecraft told me the same thing. However, as I told them, I'm on
> the second power up test in the manual, there is no T3 or PA transistor in
> on the board at this time. I've built the front panel, the control board
> and the receiver, no transmitter yet. I'm pretty sure its something in the
> 12v line, I just can't find it. I wondered about F1 but I show 12 volts on
> both sides of it so I guess its ok. And the power supply is fine, I have 12
> volts on the RF board until I push the on switch on my front panel. Then the
> voltage drops to about 2.5. I figure something is pulling it down, I just
> need to find it! Thats what I get for building when I have to have my
> magnifying glasses on the see anything on those boards!
>
>

Mark Bayern

Re: K2 DOA at second power up test

In reply to this post by ke4d

Maybe try a different 12V source? I'm wondering if the short might
have damaged the supply.

Mark AD5SS

On Mon, Nov 7, 2011 at 4:53 PM, ke4d <[hidden email]> wrote:

ke4d

Re: K2 DOA at second power up test

In reply to this post by Don Wilhelm-4

Got it. Thanks Don. When I removed the 78L06, good things happened. Now I just have to determine if that is the culprit or something else in that part of the circuit. Love the reflector. Its saved me more than once!