Using Digital VM? (Control Board K2 # 5422)

[Fred (FL)]

I could use someone's help - to understand the
"resistance" measurement values, at the end of each
PCB's completion in manual.  I tried making readings
with an analog VM and got values too small for some of
them.

At a K2 builder's recommendation - I bought an
auto-ranging DVM.

In measuring resistances for Control Board,
(page 21 table).  On a few Control Board measurements,
I'm getting MUCH higher resistances than table
indicates:

  U6 pin 13  supposed to be > 100k   got INFINITE
  U6 pin 14  supposed to be > 100k   got INFINITE
  U6 pin 29 & 30      to be > 70k    got 85k
  U8 pin 2            to be > 100k   got 6.6meg
  U8 pin 15 & 16      to be > 100k   got INFINITE

The INFINITE measurements I got for a few of the IC
pins - were right up there, like an "open"?  I don't
know how to interupt this with a DVM?  

Do these readings sound reasonable?

Thanks, 73's
Fred N3CSY

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[Dan Barker]

Yes, INFINITE is greater than 100K, 85 is greater than 70. You are good to
go! Fire up that soldering iron!

Dan / WG4S / K2 #2456

<snip>
  U6 pin 13  supposed to be > 100k   got INFINITE
  U6 pin 14  supposed to be > 100k   got INFINITE
  U6 pin 29 & 30      to be > 70k    got 85k
  U8 pin 2            to be > 100k   got 6.6meg
  U8 pin 15 & 16      to be > 100k   got INFINITE
</snip>

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[John E. Reiser]

> Do these readings sound reasonable?

Hi Fred,

I worried about the same thing when I built K2 #4970.  I called Scott at
Elecraft and he told me those readings were perfect.  And if you take the
manual literally, they absolutely correct.  (Infinite is > 100k, isn't it?)

Anyhow, I just went on with my building, and had no problems.

73,

John, W2GW


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[Ron D'Eau Claire-2]

Fred, N3CSY, wrote:  

..."resistance" measurement values, at the end of each
PCB's completion in manual.  I tried making readings
with an analog VM and got values too small for some of
them...

---------------------
You've got the "good word" about those measurements, but your comment
concerned me! Be very careful to ensure that any analog meter you use for
resistance checks is designed for use with solid-state circuits! Many of the
wonderful, top-of-the-line-for-their-day analog volt-ohmmeters (VOMs) can
destroy modern solid state devices.

The problem is that they apply too much voltage and allow too much current
to flow through the circuit under test when making resistance measurements
in modern solid-state circuits! It's often plenty to destroy devices
instantly.

Ron AC7AC

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[Ken Alexander-2]

I've always been confused by this kind of direction.
For example:

101k is also greater than 100K, but what's better:
101k or infinity?  Infinity could also indicate an
unsoldered circuit board connection or that someone
inserted a capacitor where a resistor should have
gone.

">100k, as high as infinity" or ">100k, 180k typical"
help me a lot more, where it's possible to state it.

73,

Ken Alexander
VE3HLS


--- Dan Barker <[hidden email]> wrote:

> Yes, INFINITE is greater than 100K, 85 is greater
> than 70. You are good to
> go! Fire up that soldering iron!
>
> Dan / WG4S / K2 #2456
>
> <snip>
>   U6 pin 13  supposed to be > 100k   got INFINITE
>   U6 pin 14  supposed to be > 100k   got INFINITE
>   U6 pin 29 & 30      to be > 70k    got 85k
>   U8 pin 2            to be > 100k   got 6.6meg
>   U8 pin 15 & 16      to be > 100k   got INFINITE
> </snip>
>
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[Mike WA8BXN]

 
The purpose of resistance checks is not to detect and diagnose all errors
but rather to prevent the release to the magic smoke contained in components
when you apply power.
 
-------Original Message-------
 
From: Ken Alexander
Date: 03/28/06 13:25:42
To: Dan Barker; F and J; [hidden email]
Subject: RE: [Elecraft] Using Digital VM? (Control Board K2 # 5422)
 
I've always been confused by this kind of direction.
For example:
 
101k is also greater than 100K, but what's better:
101k or infinity? Infinity could also indicate an
unsoldered circuit board connection or that someone
inserted a capacitor where a resistor should have
gone.
 
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[Dan Barker]

I discovered that if you let out enough of the magic smoke fast enough,
there are some follow-up orange flames inside those components too! Usually,
I'm only klutzy enough to allow some (or all) of the magic smoke out, but
recently I went even farther!

I had replaced the SLA batteries (2 @ 12v, 7AH each) in a UPS. I did turn it
off, but neglected to remove the AC cord from the socket. I was pulling the
metal case over the unit to secure it, and it contacted two (minimum, maybe
more) places it shouldn't.

I blew on the chips as hard as I could (more than at a birthday cake, I
assure you) and did manage to make the orange flames reenter the chips, but
alas, enough of the magic smoke was gone. Sigh.

Dan / WG4S / Belkin F6C-120

<snip>
The purpose of resistance checks is not to detect and diagnose all errors
but rather to prevent the release to the magic smoke contained in components
when you apply power.
</snip>

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[Ron D'Eau Claire-2]

The resistance readings may vary widely depending upon the polarity of the
leads attached and the individual DMM used, especially when there's a
transistor or diode junction somewhere in the circuit.

Also, most DMMs read "INFINITE" whenever the value exceeds its maximum
range. That can be a few megohms for some DMMs and many megohms for others,
so it's not possible to know when the builder will see "2.6 megohms" or
"INFINITY" or, equally disturbing to some builders, "OVER RANGE" which
simply means the meter can't measure it.

At the other extreme are typical permissible variations in the accuracy of
DMMs and in the tolerance of the components in the circuit that affect
readings.

Those things also conspire to make it virtually impossible to try to
establish "typical" resistance values in a great many situations. Besides,
just what is "typical", within 10%, 50%...?

So values are chosen that, if the circuit is correct, the vast majority of
DMMs display measurements that agree with those shown in the manual. Some
will be closer to the limits given than others by orders of magnitude, but
as long as the reading agrees with the manual you're okay.

If you have a reading that simply "feels" close, try reversing your test
leads and see what happens or, if you have one, try a different DMM.

Ron AC7AC

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[Don Wilhelm-3]

I is not meant to confuse anyone, but must take into consideration all
possible variables.

If one were to look at the schematic and understand which components are
installed and which are not at the point when you make those measurements,
you will understand why the readings are so high - many of the early checks
are for signal paths that go off the board and they are connected to
nothing - so you should read an 'infinite' resistance - the real reason for
the check is to be certain there is nothing shorted.

So why does the manual indicate '>100k' when the actual expected resistance
should be infinite? you may want to ask.  I don't know for certain, but I
would not put out a kit that would be tested with a large variety of DMMs
and state it any other way - there is no way that the manual writer can
predict how your particular DMM will respond to an open circuit, plus, if
one gets a part of his body in contact with the path being measured, the DMM
will likely indicate some actual resistance, I have one that reads abotu
400K across my finger, and I have another that reads about 3 megohms - of
course that depends on how much moisture I have on my skin too.  So ther is
no way to communicate properly for all meters and measurement situations
other than to state that a reading above 100k is just fine.

73,
Don W3FPR

> -----Original Message-----
>
> I've always been confused by this kind of direction.
> For example:
>
> 101k is also greater than 100K, but what's better:
> 101k or infinity?  Infinity could also indicate an
> unsoldered circuit board connection or that someone
> inserted a capacitor where a resistor should have
> gone.
>
> ">100k, as high as infinity" or ">100k, 180k typical"
> help me a lot more, where it's possible to state it.
>
> 73,
>
> Ken Alexander
> VE3HLS
>

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