No, that wasn't a mouse in the heater

Discussion in 'Generation 1 Prius Discussion' started by ChapmanF, Aug 30, 2014.

  1. ChapmanF

    ChapmanF Senior Member

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    It sounded pretty convincingly like a mouse scrabbling around in the heater, but it was just the air mix damper mechanism jittering back and forth because (like so many other things in the Gen 1 that use a potentiometer to give position feedback), the contacts had become noisy and it was trying to "hold" position while the position signal jumped around.

    PriusChat won't let me upload servo.webm as a video, but if you want to see/hear the action you can download servo.webm.zip and unzip it and view it.

    The manual says to remove the instrument panel (!!) to reach this guy, which is ludicrous. Duck under the steering column and you're looking right at it; three Phillips screws out and it's in your hand. It's trivial to take apart, no Dremeling or gluing. A cotton swab with a contact cleaner/lube like GC Jiffy Bath and it's all steady and quiet again.

    servo.jpg servogear.jpg

    -Chap
     

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    #1 ChapmanF, Aug 30, 2014
    Last edited: Aug 30, 2014
    depriusoto, Mendel Leisk, SFO and 3 others like this.
  2. bwilson4web

    bwilson4web i3 and Prime

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    I'm glad the repair worked but I've been pursuing the 'tin whisker' hypothesis. My testing of failed accelerator pedal encoders suggested a 9V battery while running the part stop-to-stop will 'burn out' the existing whiskers. It is not a permanent fix nor would cleaning because tin whiskers form spontaneously. But 'burning them out,' would in theory subject the nucleating source to a thermal stress . . . whacking that mole.

    Regardless, excellent description of the part and location.

    Bob Wilson
     
  3. ChapmanF

    ChapmanF Senior Member

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    I guess something that hasn't been clear to me is ... does every instance of potentiometer noisiness turn out to be an instance of tin whisker growth? The way I thought I understood it, tin whiskers have been an increasing nuisance since the elimination of lead from solders and tinning alloys, but even old vintage stereos and such that go way back into the tin-lead days still get "noisy" pots and switches, which the old-timey way to fix was to squirt in contact cleaner and work it around, which does still seem to work. (In fact, I need to do that on my old vintage stereo again when I get a chance.)

    Does the 'contacts get dirty/oxidized' hypothesis still account for anything these days, or do tin whiskers always turn out to be the real culprits?

    -Chap

    p.s. I guess when my steering gear was going, I did drive around for a while with a chart recorder and catch that the glitches really did look like spikes toward ground, as if perhaps being shorted by a whisker. I didn't do any similar data gathering to see just what the signal looked like from this servo ... it's too easy to just take it out, clean it up, and say 'next project'.
     
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  4. bwilson4web

    bwilson4web i3 and Prime

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    I won't rule out 'crap in the gap' but the encoders Doug pioneered in cleaning and my subsequent sustaining efforts never found any visible debris. Then the NASA tin whisker analysis of a failing Camry encoder and my subsequent 'burn out' tests suggested this is the likely root cause.

    My ears are open but did you see visible debris on the cleaning material? Tin whiskers are very, very, small almost invisible to the unaided eye.

    Bob Wilson
     
  5. Mike500

    Mike500 Senior Member

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    The RoHS rules that limit cadmium and hexa-chrome compounds that are less likely to "wisker" than tin and zinc doesn't help much either.
     
  6. Darla

    Darla New Member

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    I'm having trouble viewing your video. It allows me to view it but not hear the audio. I'm trying to figure out if the sound my car is making near the dash is similar to yours. If you have time to check out my post with my video and let me know if this is what it sounded like for you, I would really appreciate it!

    Please Help, Noise Behind Dash! | PriusChat
     
  7. ChapmanF

    ChapmanF Senior Member

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    I listened to yours when you first posted it, and I found the audio so faint I couldn't decide anything from it ... that's why I linked from your thread to here.

    It's odd that you're not getting audio from my webm here. I just downloaded it straight from PriusChat myself and played it to see if something might have happened to it on PC's servers, but it plays just fine for me, after unzipping, either in Firefox or with mpv. The audio is rather loud, as I boosted the level before uploading it.

    Maybe try another browser or media player for playing it?

    -Chap
     
  8. Diemaster

    Diemaster Member

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    this. grant it ROHS solder is difficult to work with.
     
  9. ChapmanF

    ChapmanF Senior Member

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    All the same, pots do just get dirty/noisy with time, and have done since long before ROHS. I have an elderly vintage stereo preamp whose volume and balance knobs will inevitably get noisy and need the occasional teardown and spray with Jiffy Bath, and I had a turntable whose speed regulation would get all jumpy every few years until I sprayed down the 33/45 button contacts and the fine-adjust pot. Ask me if that was annoying! (And not just because it sounded awful, but the disassembly to reach those parts was really tedious.)

    My method for cleaning up the heater servo was just to open it up and swab down the pot contacts and paths with Jiffy Bath, same as my lifelong procedure for cleaning any similar thing, and it worked and the thing held rock-solid position after. Now, Bob's speculations about tin whiskers are attractive because they suggest a possible fix with a nine-volt battery and no disassembly needed, and I am not saying for sure that approach wouldn't work; I never tried, so I don't know. All I'm saying is I approached the problem as a classic dirty pot scenario, and that approach worked out well for me.

    -Chap
     
  10. audiodave

    audiodave Active Member

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    Any electronical contact like that has the potential to oxidise and or get dirty.

    Posted via the PriusChat mobile app.
     
  11. ChapmanF

    ChapmanF Senior Member

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    A satisfied customer. :)

    For future reference, the Gen 3 Prius replaced these actuators having potentiometer-style feedback with a new design using Hall-effect sensors for the feedback. So this should be a very uncommon issue in Gen 3 or later. Gen 1s and 2s are likely to experience it as they age, and as you can see, it's very easy to fix.

    The one exception might be if the air-inlet damper is the one that gets noisy. The other two servos (air mix for temperature, and outlet select) are on the easy-to-reach side of the heater case. The air inlet one is much harder to reach on the other side of the case, sandwiched between it and the blower. The dash might really have to come off to reach that one. I never had to do it (had my Gen 1 up to 230,something thousand), but it is built the same as the other two, so somebody keeping a Gen 1 or 2 super long might eventually have to deal with it.

    -Chap
     
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