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Climate control display (300m) - no display

Discussion in 'LH: Large Cars, 1993-2004' started by MoPar~Man, Jul 10, 2017.

  1. MoPar~Man

    MoPar~Man Member

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    I noticed today that the climate-control display on my 300m is not lighting up. The buttons seem to work and do what they're supposed to. This is a gas-discharge display technology - yes?

    Is there anything known about the failure modes of the display? In other words, could be a fuse or some easy-to-fix discrete component on the board, or is the display tube dead?
     
  2. Best Answer:
    Post #6 by Tomguy, Jul 25, 2017
  3. MoPar~Man

    MoPar~Man Member

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    Strange. I took the display unit apart, looked at the board and the glass display element, didn't see anything burned, put it back together and reconnected the single plug but didn't press the bezel (with the unit) back into place in the dash, just sort of left it propped up against the dash. Started the engine - and the display unit was now working. Pressed the two top bezel clips into place - the display goes dark. Pull the bezel back out - the display is back. Gonna have to look into this some more ...
     
  4. ImperialCrown

    Level III Supporter

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    If it is affected by mechanical flexing, it sounds like broken solder joints on the board? The cracked joints can be reflowed with a small soldering iron:
    cracked.jpg
     
    valiant67 likes this.
  5. 2012srtchallenger

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    They are not cheap but had best luck with new ones from dealer,no more display problems.might get lucky and find good used one
     
  6. Tomguy

    Level 2 Supporter

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    They are known to do this.
    The solder at the 3 resistors that drive the board cracks with age. Re-flowing them fixes it up. It's easy if you know how to solder.
    Luckily for you I have a spare on my desk, I'll snap a pic with my phone & reply with it.
     
  7. Tomguy

    Level 2 Supporter

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    http://i.imgur.com/gdPdqaK.jpg
    Note: As you can see, on my "Spare" the resistor actually fell off. These three need to be re-flowed.

    Pull out the bezel surround (no screws hold it in). Unclip the wire from the control module. Use a small socket (I want to say 3/16"?) to remove the screws holding it to the bezel. Pull the knob off. Remove the 2 phillips screws holding the fan to the board/backing. Pull the fan off. Remove the other 3 screws. With the unit face-down pull the PCB off. Don't lose the small plastic inserts by turning the face upright. Solder & re-attach the board. Now's also a good time to replace any burnt-out backlights.
     
  8. MoPar~Man

    MoPar~Man Member

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    Yea, I just had a look at those 3 resistors under a microscope. Micro-gap had formed on the ends of all 3. I metered across the pads and found them to be open. Maybe they had never been properly soldered in the first place. I applied more solder, made sure it flowed properly on the ends. Seems to work fine now. Thanks for the info. Way to many solder points to try this at random.
     
    Tomguy and ImperialCrown like this.

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