lights out on AC Panel in 98 C280
 

I looked for an existing thread on this subject with no luck. If there is one, please excuse me and point me in the right direction.

I just noticed, a few nights ago, that the back lighting on my LCD panel for the heat/ac controls is out. Not sure if it is related, but the light on my nearby "ASR" switch appears to be out. I have gone through what meager info I have with no mention of this.

Any thoughts out there guys?

Thanks!

Is it the illumination behind the ACC panel buttons or the LCD display. If it's the display, bad news. There is no easy way to replace the bulb.

Ouch! It's the backlighting in the LCD display. Soooooo, do I have to replace the entire module to get this fixed? If so, do you know where I can obtain one of these? I have an electronics background. Might it be possible to extract this monster and actually repair it? Probably not, if it is like most LCD backlighting technologies?

Thanks!

FYI the bulb in my 97 went last summer. The original bulbs seem to last6-7 years as I have seen a couple others being replaced by members at that time.

So there IS a bulb for the LCD backlighting? Did you replace it yourself or go to someone?

Later that same day.....

While reading a UK MB forum, I did find out that it uses a regular "bulb". However, I have been unable to find anyone that can tell me the correct way to "get to the bulb"! I bet it's a royal pain to remove that LCD panel...... :confused:

The climate control pushbutton module should pull out with the radio pulling tools. I have never needed to replace the bulb in my car, but I remember when my dad had the car he had the dealer change it once and I think it was like $35, so its probably not that hard to do but I could be wrong.

I changed the bulb in my W210, it wasn't a big deal to pull out the climate module, I cut off an old creditcard and slided it into the slots on each side and pulled the module gently out.

Morgan

That sounded very ingenious, so I created my "credit card tools" and tried it. I examined the entire perimeter of the climate control module, but could find no "slots" or even enough slack to wedge the "tools" into. There is only a very minute amount of slack between the front of the module and the mounting surface. I am not familiar with the climate module of the W210, but it must be different from the one in my C280?

I am not familiar with the "radio pulling tools", but I will GET familiar soon!

Thanks so much for your input!


Added later...

I know this is probably so wrong, wrong, wrong... but I seemed to have found my answer on "another forum". <please don't kick me off!> Hopefully they won't mind me posting the link? I want you guys' opinions if they are correct!

http://www.mercedesforum.com/m_7095/mpage_1/tm.htm#11431

Using a picture of the standard Mercedes "radio removal keys", I guessed at the dimensions (after looking at the size and depth of the "key holes" and built two keys from some leftover FR4 double-sided copper-clad circuit board that was thrown away at work using a metal brake and nibbler. It took about 2 minutes. I would suggest using something stronger like sheet metal or buy them from an MB dealer or Ebay!

I carefully inserted them into their slots at the extreme lower left and right side of the climate control module with the gaps on each key facing inwards. Gently pushing them to the end of their travel, I could feel the module loosen up and was able to remove it very easily with my fingers.

The white plastic light "bulb" was in the center of the bottom of the module. I turned it a quarter turn and removed it with small needlenose pliers. (It seems to take a little coaxing to get it out) The bulb is a tiny 12 volt DC "wheat bulb" and is actually installed in a small socket that is pushed into the main receptacle. If you don't have a MB dealership around, you can actually remove the tiny bulb by straightening its two wires and pulling it from its socket. The bulbs are available at Radio Shack and other electronic supply houses. Some auto parts places may have similar bulbs you could use. Just push the two wires through their corresponding holes and trim them to fit. Push the bulb back into the main receptacle, install it into the climate control module, put the module (without the removal keys!) back into the dash and voila! Back in business!

Thanks so much for all the input and help, guys! You rock!

I am going to buy the special "radio removal keys" next time I am by the MB dealer! They are worth the money to keep around, just in case!

What a great find! Dealers often sell entire units based on the failure of the LCD panel light. Excellent work!

Okay, but as the radio announcers say, "But wait! There's MORE!" :eek:

I removed the bulb and tested it with my dvm and it does show open. Now I replaced the bulb with the new one, turn on the ignition key and the headlight switch, no light.... hmmm... So I remove the NEW bulb and test its continuity with the dvm, shows about 13 ohms. Ok, that's a static test, so I put it on the bench with a 12 VDC power supply, bulb works admirably. I check the power at the contacts of the mating area of the control module, turned on the lights and it measured 12 vdc, so there IS power to the light socket (how much current is available at 12 vdc, I don't know as yet).

Now the weird rookie question: I was reading a thread somewhere along these lines that mentioned a "rheostat". Does this model have one and if so, where the heck is it? ha ha ha!


Later that same day!

I finally discovered the problem. I took the intricate little "socket" into our lab and put it under a microscope. The socket is an assembly consisting of 2 nylon parts and 2 metal parts. The 2 metal contacts appeared to be both dirty AND corroded from the heat of the little bulb. Using isopropyl alcohol (also known as isopropanol to some chemists or RUBBING alcohol to us southerners!), I cleaned the entire thing, brushed the contact areas a tiny bit, bent the two outside contact areas UP a little, then reassembled it.

I put the assembly back into the module and tested it and it now works!

I'll try and take a few pictures and add to this thread later if anyone would like it.

Hi Clankford,

Nice to see another electronics guy on the site. First, if you have a good bulb and you have 12V then explain to me why it doesn't light up??? Well, either you have a high impedance path or a bad connection right? So check your 12V at the bulb with the bulb connected. My favorite saying as a bench tech was "if you prove that it must work then it will work". As far as the rheostat, the dash light brightness is controlled by the "+" "-" buttons which are above the "0" button (odometer reset) on the lower left edge of the inst panel surround. I assume it would control that bulbs brightness also but I don't see what that has to do with anything. Anybody with FR4 in their garage should be able to fix a light bulb!!

Mike

Ha ha ha! You would think that, right? Sometimes I amaze myself at my own stupidity and ineptness. But I don't keep FR4 in my garage.... er, uh, at least not MUCH FR4. I had it at my job.

I had thought that I might be dealing with a high impedance issue, so I decided to check all the contact areas first.

Well, it is working now, but dimmer than I would like, so the next time I go by an MB place, I will get the exact bulb replacement. My finance is heading south to the coast in my Benz, so I am trying to get all those last minute things fixed.

Thanks so much!

Your "finance"? Is she costing you that much???

MP