K2 resistance checks (and K1/KX1)

[g3ymc]

We see frequent mails on here from people doing the resistance checks
in the manual and reporting they get (say) 100k when the manual says
>500k or whatever. There is some implication in the manual that these
values are set in concrete and you shouldn't proceed if they are not
met to the letter. Of course we all know that they are checking for
direct shorts or similar and measurements somewhat outside the values
stated do occur and do not mean a catastrophic error.

When measuring with a digital meter, which most of use, the value
recorded when measuring components shunted by semiconductors,
capacitors and other non linear things will differ enormously between
different meters and nothing can be deduced from the reading other
than it is not short circuit!

I know there are comments in the manual that you may get different
readings from those shown, perhaps that needs expanding a little. Or
maybe in light of experience that most people have few problems in
building their rigs the resistance tests should be omitted.

73 Dave G3YMC

http://www.davesergeant.com

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[Brian Mury-3]

I had a resistance check that was supposed to be >500, I got around 370.
I thought, as you've said, that it was no big deal - turns out it was a
big deal. The resistance check not only indicated that there was a
problem, but also helped me know where to look.

The resistance checks can be useful.

On Wed, 2004-06-23 at 03:34, Dave Sergeant wrote:

> We see frequent mails on here from people doing the resistance checks
> in the manual and reporting they get (say) 100k when the manual says
> >500k or whatever. There is some implication in the manual that these
> values are set in concrete and you shouldn't proceed if they are not
> met to the letter. Of course we all know that they are checking for
> direct shorts or similar and measurements somewhat outside the values
> stated do occur and do not mean a catastrophic error.
>
> When measuring with a digital meter, which most of use, the value
> recorded when measuring components shunted by semiconductors,
> capacitors and other non linear things will differ enormously between
> different meters and nothing can be deduced from the reading other
> than it is not short circuit!
>
> I know there are comments in the manual that you may get different
> readings from those shown, perhaps that needs expanding a little. Or
> maybe in light of experience that most people have few problems in
> building their rigs the resistance tests should be omitted.
>
> 73 Dave G3YMC
>
> http://www.davesergeant.com
>
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--
73, Brian
VE7NGR

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[Don Wilhelm-2]

Brian and all,

If the resistance reading should be >500 and one measures something LOWER
than 500 ohms it SHOULD be something to check carefully - it is the reading
that are higher than 500 that are 'no big deal'.

The more commonly asked question is from folks who measure something
substantially higher - and the proper answer to that IS that it is no big
deal (that is exactly why the 'greater than' symbol is used in the manual.
Perhaps these questions come from those not familiar with the 'greater than'
symbol (>) - I can only guess.

73,
Don W3FPR

Life is what happens when you are making other plans

----- Original Message -----

> I had a resistance check that was supposed to be >500, I got around 370.
> I thought, as you've said, that it was no big deal - turns out it was a
> big deal. The resistance check not only indicated that there was a
> problem, but also helped me know where to look.
>
> The resistance checks can be useful.
>
> On Wed, 2004-06-23 at 03:34, Dave Sergeant wrote:
> > We see frequent mails on here from people doing the resistance checks
> > in the manual and reporting they get (say) 100k when the manual says
> > >500k or whatever. There is some implication in the manual that these
> > values are set in concrete and you shouldn't proceed if they are not
> > met to the letter. Of course we all know that they are checking for
> > direct shorts or similar and measurements somewhat outside the values
> > stated do occur and do not mean a catastrophic error.
> >
> > When measuring with a digital meter, which most of use, the value
> > recorded when measuring components shunted by semiconductors,
> > capacitors and other non linear things will differ enormously between
> > different meters and nothing can be deduced from the reading other
> > than it is not short circuit!
> >

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[Brian Mury-3]

> Perhaps these questions come from those not familiar with the 'greater than'
> symbol (>) - I can only guess.

Or from people thinking it's "too much" greater than - I did have that
thought the first time I saw > 100 k and measured a few M. I decided it
was ok and carried on...


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[Ron D'Eau Claire-2]

One of the problems is that when you measure the resistance to ground in a
circuit that contains solid state devices, the value can vary widely because
of the meter you are using. Different makes of DMM's use slightly different
voltages for the ohms sense and that can cause widely varying readings in
the resistance in a "normal" circuit. That's because often the value of
resistance you are seeing is not the value of several resistors, but is
instead a slight forward conduction through junctions of transistors, and
diodes.

Also, that is why it's so important to only use a meter designed for
solid-state gear. Many older "VOMs" use sufficient voltage and allow
sufficient current to destroy solid state devices. But even among the DMMs
designed for solid state circuits, the values reported when "looking"
through junctions in IC's or transistors can vary widely.

Add to that the desire to be sure that when the book says "greater than" (>)
there follows a value that NO DMM is expected to show less than if the
circuit is correct, and sometimes the actual value your DMM reports will be
orders of magnitude larger. For example, your DMM may indicate several
megohms when the book says ">100k ohms"

Ron AC7AC

-----Original Message-----
> Perhaps these questions come from those not familiar with the 'greater
> than' symbol (>) - I can only guess.

Or from people thinking it's "too much" greater than - I did have that
thought the first time I saw > 100 k and measured a few M. I decided it was
ok and carried on...


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