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Re: [RFI] Whirlpool 465 Oven Door Latch Solenoid RFI

To: <rfi@contesting.com>
Subject: Re: [RFI] Whirlpool 465 Oven Door Latch Solenoid RFI
From: "Ward Silver" <hwardsil@gmail.com>
Reply-to: Ward Silver <hwardsil@gmail.com>
Date: Sun, 10 Jan 2010 17:36:03 -0600
List-post: <rfi@contesting.com">mailto:rfi@contesting.com>
>> Strong RF from a low dipole is triggering the door latch solenoid on a 
>> Whirlpool 465 gas oven.  I installed an ac
>> line filter but that didn't change anything.  I have a training manual 
>> that shows the wiring for the solenoid and the
>> next step will likely be adding ferrite corres to the controller followed 
>> by adding an on-off switch to the solenoid
>> since it's only activated during the self-cleaning cycle. However, if 
>> anybody has cured a similar problem, I would be
>> interested in hearing how you did it.
>> the next step will likely be adding ferrite corres to the controller
> Remember to wind enough turns through the cores to move their
> resonance down to the frequency range that excites the problem.
> Some other thoughts.
> Consider the current path of the relay as an RX antenna (or magnetic
> loop). If possible, rewire it with twisted pair, so that the signal
> return is twisted with the hot lead. Doesn't matter for DC, but it
> sure does for RF. You don't need to break the other return path -- RF
> will follow the path of least impedance (inductance), which is the
> twisted pair.
> If there is some sort of high-Z sensing circuit that drives the
> controller, try a bypass cap across it.
> 73,
> Jim K9YC

I neglected to note that the controller also winds up with a "sensor 
over-temp" error after an extended bout of operating. (This is good, because 
it makes the controller stop clacking the solenoid until I press the OFF 
button.)    Plus, the solenoid does not activate in the pattern of the 
keying (which would sound interesting), but rather as if the controller has 
detected the "activate solenoid" condition.  So I am pretty sure the RF is 
getting into the controller by multiple paths, not just the relay driver.

I'll check with Whirlpool on an RF fix and assuming they don't have a fix 
will then begin the process of trying to isolate the interference path, 
reducing loop area, bypassing inputs, etc.  Thanks for the comments thus 

73, Ward N0AX 

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