HW100 nightmare

[Jeramy Thibodeaux]

David,

I believe what you are saying is true where voltages are concerned.  Factors 
contributing to this phenomena are the age of components especially 
capacitors that have increased in ESR, the type of meter used to initially 
make the measurements compared to the type of meter used today, questionable 
calibration of the test equipment, and changes in supply voltage over the 
years from the 110V to the 120V standard are just a few.

One thing that could make what you are saying true.  If the resistors are 
measured in circuit the value could read out of tolerance on the low side. 
This usually means that there are other resistors or components in parallel 
with the resistor being measured.  The circuit will have to be broken by 
de-soldering one lead of the resistor and lifting it out of the circuit. 
Then the resistor can be measured and verified that it is within tolerance.

I have to agree with Herman that it is cheap and can solve a lot of the ills 
by simply replacing any resistor that is measured with a DMM and found to be 
grossly outside of it's rated tolerance.  It is well documented about the 
problems associated with carbon composition resistors changing value with 
age and heat.  Some circuits tend to be more forgiving to component changes 
than others or the circuits were intentionally designed with a means to 
adjust the tolerance.  Using a properly calibrated analog meter should give 
similar indications even if they do not show the exact same value as the 
DMM.

Jeramy
kg4azt




----- Original Message ----- 
From: "David Goncalves" <davegoncalves at GMAIL.COM>
To: <HEATH at LISTS.TEMPE.GOV>
Sent: Friday, March 19, 2010 7:40 PM
Subject: Re: [HEATH-TEMPE] 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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