VCO Oscillator Test Problem

[Gottlieb, Jonathan]

I am building K2 4856.  I've run into a real problem. All tests have gone great until the VCO Oscillator.   In doing the VCO Oscillator Test I get a reading of 00000 AND Q1, Q2, Q3 and Q4 on the Control Board all got very hot.  Hot to the touch.  Not sure where to go with this one.  Any suggestions?

Jonathan Gottlieb
WA3WDK
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[Don Wilhelm-3]

Jonathan,

I can understand Q1 and Q2 getting hot from a shortcircuit somewhere on the
8T and 8R lines, but I just don't understand how Q3 and Q4 would get hot -
they are just switches and should be fully conducting or fully
non-conducting (and therefore should dissipate very little heat).  Start by
checking resistances on the 8T and 8R lines and search for that elusive
solder bridge that I suspect is somewhere on the RF board or the Control
Board.

After you cure the cause of Q1 and Q2 heating excessively, you can move on
to the VCO problem if it still exists.

73,
Don W3FPR

> -----Original Message-----
>
> I am building K2 4856.  I've run into a real problem. All tests
> have gone great until the VCO Oscillator.   In doing the VCO
> Oscillator Test I get a reading of 00000 AND Q1, Q2, Q3 and Q4 on
> the Control Board all got very hot.  Hot to the touch.  Not sure
> where to go with this one.  Any suggestions?
>
>


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[Margaret Leber]

W3FPR - Don Wilhelm wrote:

> I can understand Q1 and Q2 getting hot from a shortcircuit somewhere on the
> 8T and 8R lines, but I just don't understand how Q3 and Q4 would get hot -
> they are just switches and should be fully conducting or fully
> non-conducting (and therefore should dissipate very little heat).

Yes, I recently was dealing with a shorted 8R and was quite convinced
that all four transistors were hot.

In fact it was just that Q2 was so hot it was heating up the other
transistors nearby....and it was hard to tell Q2 was hotter than the
others because it was too hot to touch for long enough to tell.

   73 de Maggie K3XS

--
-----/___.   _)Margaret Stephanie Leber CCP, SCJP/"The art of progress /
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