[R-390] Measuring Resistance Values

[Jordan Arndt]

Barry...

Are you referring to resistance measurements at the component level, or at 
the resistance check points described in the manual...?

At the compnent level, I check the resistors module by module and replace 
where necessary and then check at the resistance check points if that's 
found to be necessary because something isn't working properly.

Given the heat produced within an R-390, I'd be surprised if there aren't at 
least a handful of resistors that have drifted a long way out of 
tolerance...

My 2 cents worth....73...Jordan VE6ZT

----- Original Message ----- 
From: "Barry" <n4buq at knology.net>
To: "Bob Camp" <kb8tq at n1k.org>
Cc: "R-390 Mailing List" <r-390 at mailman.qth.net>
Sent: Monday, September 02, 2024 10:57 AM
Subject: Re: [R-390] Measuring Resistance Values


> Hi Bob,
>
> Actually I was checking both. It was the resistance values which were 
> extremely high and I was trying to make sure it wasn’t because of the 
> meter I was using and I suppose it wasn’t.
>
> When I get it reassembled, I can check voltages with something more 
> appropriate.
>
> Thanks,
> Barry
>
>> On Sep 2, 2024, at 11:33 AM, Bob Camp <kb8tq at n1k.org> wrote:
>>
>> Hi
>>
>> Ok, I’m guessing we have a typo.
>>
>> We’re measuring voltage at the test points rather than resistances. Let’s 
>> see, I’ve probably only made about 10 typo’s in this message so far … :) 
>> :)
>>
>> Some of the old VTVM’s had pretty crazy input impedances. It would a bit 
>> unusual to find one that was above 10 Meg *and* something you would use 
>> in a radio with hundreds of volts running around in it.
>>
>> Something like a Simpson 260 would be a much lower input impedance device 
>> when set up for looking at test point voltages. Simple answer in this 
>> case, grab that Simpson and see what it reads.
>>
>> Bob
>>
>>> On Sep 2, 2024, at 10:31 AM, Barry <n4buq at knology.net> wrote:
>>>
>>> Did Collins specify what input impedance a meter should be to properly 
>>> read the resistance values in the manuals?  I did see where a TS-352 was 
>>> mentioned but that's selectable between 20,000 ohms/volt and 1,000 
>>> ohms/volt.
>>>
>>> I started checking the RF Deck in my R-390 and, starting with V201, I 
>>> noted a few values that are significantly high.  I was using a modern 
>>> DMM with 10M input impedance so not sure if that could be the problem 
>>> but I doubt it would account for that much difference but who knows.
>>>
>>> The voltages were off a bit as well but not nearly as much as the 
>>> resistance values.  I suspect the radio will still work with wacky 
>>> voltages but the R values really have me thinking I have work to do.
>>>
>>> Thanks,
>>> Barry - N4BUQ
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>
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