revisiting infrared remote system malfunction

[pep]

A while back(around two weeks ago) I posted at the TECH FORUM, the malfunction that I have in my SL500 1994 remote infraed system. It works perfectly during the night hours or in the dark, but when there is light hitting any of the door handles or the trunk lock, the remote system doesn't work at all or works only on the passenger's door lock at times, but not many times. I didn't mentioned when I previously posted that the key does not work on the driver's door side. And it is here where I seem to have the biggest problem with the infrared or remote entry because during daylight it does not work at all. I may also say, that at times the trunk lock works during daylight, but is very seldomly. I haven't gotten a response from the Forum yet, but since you guys and gals owned SLs, you might be familiar with this situation, or someone is experiencing it now. Thank You Kindly, PEP

[Pete Geither]

I know this is really basic, but are you sure it has a good battery?

[pep]

Yes it has a good battery. Is the malfunction that only occurs during daylight. It is a mystery to me, but to one technician, it is the plastic , or the lense that has wore off. The alternative is buy new ones, but don't sell them as a replacement part. You're forced to buy both door handles and the trunk system because they're factory coded and like I said before they won't provide you with the little simple lenses. The whole thing costs around $800 plus dollars.

[LeaUK]

There are several of us with almost, if not, identical problems - me included. Having said this that's a very interesting point re the sunlight. I've tried associating my failures with events/weather etc and haven't managed to find a link yet. But
sunlight is one I haven't considered at all!

Now IR is VERY sensitive to sunlight.

You can buy IR filters (the plastic that you can't obtain from MB) from many electrical stores (Radio Shack etc) so perhaps buy some and place it between the remote and sensor to see if this resolves the issue. I'd be VERY interested in your results so please post back if you can.


Cheers
Lea

[pep]

Thank You for your info learoy, but now you've got me thinking differently. One technician suggested replacing the old lenses with clear ones. Is true, that if it is light that's actually interfering with the infrared key normal function, then a clear lens would make it worse. Maybe a filter between the old lens and the sensor would do the trick. I don't believe is the hot, cold, rainy weather, I live in Florida and we've had a few days going from very cold to very hot to very rainy and it always works perfectly as soon as daylight begins to dissipate. If you have other ideas let me know. Thank You. PEP

[Gilly]

MB certainly DOES sell the IR receivers, you don't need to buy the handles to replace the IR receivers. I would agree this is probably the problem. I have replaced several receivers. Check with Phil at Fastlane.

Gilly

[CDNC36AMG]

Originally posted by Learoy
There are several of us with almost, if not, identical problems - me included.

True....I still haven't gotten around to dealing with mine but based on previous threads it appears that disconnecting and cleaning the door and alarm wiring has helped some.

In addition, someone pointed out that their problem was solved when they discovered a blown fuse for the alarm.

Oddly, i have no proof that my alarm works so its possible I have the same problem.

Disclaimer - I'm no techie.

[LeaUK]

Of course the proof would be to monitor the electrical signal (using an oscilloscope) from the failing door handle IR receiver and compare it with a working one.

Or shine a little light at sensor and compare. Trouble is every time I've gone to investigate, the poxy system works without fail!!

However, with Gilly's suggestions I might just purchase new sensors all round and be done with it - at least that will eliminate them as the cause.

[pep]

By any chance, does the infrared remote system has a light sensitivity adjustment level, like some alarm systems do? If anyone has heard, or know this to be a fact, please let us know. I tested my doors and trunk during the nightime by pointing a flashlight from different angles and the light would not let it function. When I used the remote key without the flashlight hitting the receivers it worked perfectly. I used a very small and weak flashlight for this test.

[LeaUK]

pep

I also tried the flashlight test yesterday too Yep it's definately the sensors!

See thread for more info.

Lea

[pep]

After I did the flashlight test, the next morning I proceeded to put a piece of silver reflecting tape on top of the lens on the driver's side door. To proof the theory it worked. It was a very simple reflecting tape, that when lifted to the sunlight you could see light coming through, but not enough to interfere with the function of the IR door system. After a while, the tape worked intermittently but when rubbed against the lens again it worked continously. I belief that if I'm able to find a reflecting tape with the right properties and diassemble the door panels and so on, and place it on inside between the lens and the sensor it would probaly work. Another thing, My son also, went ahead and put a little saliva on the surface of driver's door lens and it worked until the it dried off. I'm first going to try my son's theory and repair the outside of the lens with a plastic repair kit that I happened to acroos see on the internet.

[pep]

I forgot to mention, that as soon as I'm finish with any of the projects I'll let you know the outcome. Thanks for all the help and ideas. PEP

[tecqboy]

Red or purple cellophane will work. In fact, red ink from a magic marker "painted" onto the old lense should work. The IR emited by the key is not a "steady" beam of light. It is modulated and coded. The modulation is tuned to a specific frequency as is the wavelenght of the IR light. The red plastic lense allows only IR wavelenghts to pass to the sensor transistor. Sunlight getting through a worn red plastic filter is de-sensitising the photo transistor. BTW If you buy a "learning" remote control for a TV set, it can "learn" and store the code for your key remote. Not practical, but interesting. If you have a junk TV remote, you can use the red plastic on that to make a new filter too. There is really nothing special about that red plastic.

[LeaUK]

I placed an IR plastic filter in front of receiver but that didn't help. Maybe the sensors used by MB have limited life but this would be rather strange.

Yesterday I polished the IR surface with plastic polish to try and remove the light scratches but that didn't make any difference! I also removed the lock and sensor to check for visable damage but couldn't see any.

Next it's off to MB to see how much these are

[tecqboy]

I am following this thread closely and I hope as you guys resolve this problem you keep us informed. As an electronics design engineer, I designed several commercial products which used IR controllers. I just spec'ed a pre-built module from a company that specialized in them. A receiver module cost us about $3. It was the entire "front end". That is, it was the photo transistor, the amplifier, the filter and the decoder all in one little package about the size of a sugar cube. In any case, I've a lot of experiene with IR and I've never seen a situation where the receiver became intermittent or de-sensitized by ambient light. They do fail, but that's it, they fail. They stop working completely. In the case of our cars, I'm thinking the problem is something like corroded connectors, cracked solder joints, or salt water damage. The receivers live in a very harsh environment. Water gets in the doors and the IR modules take a hard shock when the door is "slammed" close. I don't have this problem on my car (yet), but I would pull the receiver module and have a real close look at the circuit board and wiring. Auto electronics has to work under the roughest and most extreme conditions. Time will take it's toll.