HW100 nightmare

[Paul]

All

	You need to consider the circuit as you make measurements. Simply
measuring across a resistor in a circuit may not always result in an
accurate reading. You may have to unsolder one end of the resistor to get
the true story.

Paul

-----Original Message-----
From: Heathkit Owners and Collectors List [mailto:HEATH at LISTS.TEMPE.GOV] On
Behalf Of David Goncalves
Sent: Friday, March 19, 2010 6:41 PM
To: HEATH at LISTS.TEMPE.GOV
Subject: Re: HW100 nightmare

DMM will give some measurements outside of 20-50% of manual values. Just as
note on that.

David Goncalves
W1EUJ

On Fri, Mar 19, 2010 at 5:37 PM, Herman N4Ch <N4ch at aol.com> wrote:

> Something that's very quick and easy to do (and  safe........you do it
with
> the radio powered down and unplugged) regarding  finding the cause of
> problems such as low drive, poor sensitivity, an oscillator  that won't
> start,
> inability to get PA idling current to where it should be,  etc., is to use
> a
> simple auto-ranging digital multimeter, and simply go thru a  quick
> exercise
> of "ohming out" all those old resistors in your  transceiver.   Keep a
roll
> of masking tape handy, and whenever you  find a bad resistor, mark it with
> a
> piece of tape, and then replace the bad  resistors once you are done going
> thru the rig with the DMM.   It's  amazing how many out of tolerance old
> resistors (that look just  fine......no sign of ever overheating, etc.)
> I've
> found in old Heathkits, Swans,  Drakes, and many others.   Often they will
> be
> 2-3 times the resistance  value they should be, with the higher-wattage
> ones
> (1 and 2 watt versus 1/2  watt) being the biggest offenders.   The larger
> wire-wound types  seldom have this problem........usually when they go
bad,
> they are  open.    The old carbon composition resistors can climb in value
> significantly even if they are never used..........I hate to think about
>  how
> many virgin, never soldered to, straight-leaded NOS resistors I've  pulled
> out of the parts bins to use, only to find they had twice the number  of
> ohms they should have had.   When you replace resistors, consider  the
> newer
> film types.........my experience is they don't "drift" upward in value
>  like
> the old composition types do.   Just last week, I went thru an  old Swan
> 350
> that had poor receive sensitivity and low output.........and I  found
10-12
> resistors that were at least 50% high in resistance, and over half  of
> those
> were 1 and 2 watt ones.   Replacing them fixed all the rig's  issues.
> Resistors are simple to check and cheap to replace, and I  bet you will
> find
> several in that old HW-100 that have climbed high in  value.   Good luck.
>
> 73, Herman, N4CH.
>
>
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-- 
David Goncalves

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