Funny Tek 2445 scope problem

Dave McGuire mcguire at neurotica.com
Thu May 15 17:34:37 CDT 2008


On Thu, May 15, 2008 2:07 pm, Roy J. Tellason wrote:
>> > Case solved (I think).  It seems to matter where I ground the
>> > probe.  I
>> > pulled all of the boards out of the system, no change.  I then
>> > grounded the
>> > probe to the middle finger of the voltage regulator on the board
>> > and the
>> > sine wave went away.
>>
>>    The chassis may not be at digital ground.
>>
>>    Also watch out for the middle lead of three-terminal (78xx/79xx)
>> voltage regulators...it's not unheard of to bring them up above
>> ground a bit with a voltage divider to make them operate at different
>> voltages.
>
> The _middle_ lead is not ground on the 79xx parts!

  You're correct of course; I should've said "ground" lead.

        -Dave

-- 
Dave McGuire
Port Charlotte, FL





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