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  #1  
Old 02-25-2001, 03:52 PM
Rodgeda
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how do I find one of these for replacement?

Thanks

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  #2  
Old 02-25-2001, 10:17 PM
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What is the problem with yours and what type of car?.
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  #3  
Old 02-25-2001, 10:38 PM
Rodgeda
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I have a 1987 190E and the LCD display is mostly black. I can see only one digit if the temp readout.

Thanks

Darrell
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  #4  
Old 02-26-2001, 02:39 PM
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Most likely your Display unit is fine and the sensor is bad. But rather than make assumptions, it's a simple test to determine where the fault lies.

Start by clipping a 3,000 ohm resistor across the leads in place of the sensor. If the display is working properly you will get a readout around 77 degrees F (25C), thus confirming that the sensor is bad. (Remember that the ignition must be on.) If the readout is still blank using the resistor, check the power and ground connections to the display unit.

If the sensor is bad it can be easily replaced for less than $5. The Display unit is a different story.

Good luck, Barrie
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  #5  
Old 02-26-2001, 03:14 PM
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Black LCD displays are generally caused by broken displays.
Bad sensors generally give a strange reading, not a black display...

...don't know where to get one in the states, in europe I can find one at every possible car yard...

greetingz,

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  #6  
Old 02-26-2001, 03:42 PM
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Barrie,
Where do you get a sensor for $5? I am missing mine and would love to replace it. A factory one is about $49. Many thanks.
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  #7  
Old 02-26-2001, 03:50 PM
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The reason I was asking is that I have the same problem. Well...kind of, mine has half a display readable and the other half black. I know is the LCD display since I had taken it apart and you can actually look at the LCD glass and see where the "corrosion" has eaten the display. Unfortunately, MB doesn't sell the LCD glass by itself, you have to buy the whole unit$$$$$$. I checked a few used car suppliers a while back but, they didn't have them. May be they are available now...
Happy hunting!
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  #8  
Old 02-26-2001, 06:41 PM
MoTheMerc
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I agree with J.Hidalgo and MBENZ, usually the cause of a black LCD is due to it having been broken by being hit by something.

An LCD (Liquid Crystal Display) is made of two layers of thin glass with the liquid crystal inbetween. A 'plastic' polarising filter layer sits above all this to create the blackness - by preventing the reflection of light from the display's refelective (silver/white) backplane.

Crack the glass and the liquid gets squished into places it shouldn't be, resulting in either odd black blobs or complete blackout.

The LCD will also turn black if enough heat is applied to it, but will usually return to normal once the display has cooled down again, so it's worth making sure the display isn't getting too hot before you go replacing it!

Just to further 'confuse' the issue though, some LCDs are intentionally black, created by fitting the polarising filter back-to-front from normal, the display is then lit from behind and the light shines through the whitened segments instead. So a 'black' LCD may be caused by the backlighting bulb having burnt out.

How do I know all this? I have a degree in electronics engineering!

James, UK
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  #9  
Old 02-26-2001, 10:07 PM
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Guess I was thinking 'blank' as much as 'black', but I would still do the simple diagnostic test to be certain of what's at fault (won't cost you anything).
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  #10  
Old 02-26-2001, 10:15 PM
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Sensor Replacement

Ron,

What you get from the dealer is a sensor soldered to one end of a 2-conductor wire. This enables you to replace the sensor cable to the display connector (around the fuse box). Because of the labor involved in routing the cable through the engine wire bundle, many mechanics will just cut-off a piece and splice it to the old cable (not recommended!). Others, to avoid the splice, will desolder the sensor from the new cable and replace the old sensor.

In any event, all you need is the sensor itself which is an NTC thermistor. Units such as the Fenwal #192-302LET-A01 or Thermometrics #EC95F302W are more durable and accurate than the original spec. The Thermometrics unit, for example, lists for $3.75 and is available from electronics suppliers such as Newark and Allied.

Hope this helps.

[Edited by barrie on 02-27-2001 at 04:04 PM]
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  #11  
Old 02-26-2001, 11:16 PM
MedMech
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Ahhhh I love Newark!
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  #12  
Old 02-27-2001, 12:56 PM
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Thanks for the tip Brent, that kind of saving will be a big help.
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'76 240D-Sold
'78 240D-Sold
'85 300 SD, 165K-Sold
'88 300 TE, 165K-Sold
'64 Porsche 356C Cabriolet- under restoration
'86 560SL 124K Miles-Sold
'94 320E Wagon, 74K Miles-128K Miles JUNKED
'06 E350 Wagon, 84K Miles
07 SL550, 14K Miles
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  #13  
Old 03-12-2001, 01:08 PM
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Thanks to Barrie, I installed one of the new Fenwal probes at the end of the wire and I now have a temperature reading. However, two problems remain, 1. The temp is in C rather than F and 2., the temp is somewhat inaccurate. Does anyone know how to change the reading from C to F? and what size range of tweaking resistors to put into the line to calibrate the reading (or an other technique)?
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'76 240D-Sold
'78 240D-Sold
'85 300 SD, 165K-Sold
'88 300 TE, 165K-Sold
'64 Porsche 356C Cabriolet- under restoration
'86 560SL 124K Miles-Sold
'94 320E Wagon, 74K Miles-128K Miles JUNKED
'06 E350 Wagon, 84K Miles
07 SL550, 14K Miles
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  #14  
Old 03-12-2001, 03:17 PM
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temperature accuracy

Ron,

If you used the specified Fenwal thermistor, temperature tracking will be more accurate than the original assuming it wasn't damaged during installation. (The thermistor leads should be sinked with clips when soldering.) A trimming resistor is not a solution in any event since the thermistor and display curves are not linear.

It is easy enough to test the accuracy of both the thermistor and the display unit, but first a couple of questions. How much of an error are you getting? Where is your sensor located -- in front of the radiator or in the left front bumper?

The reason your temperature readings are in C is because that's the version of your display unit. You could replace it with an F-display version, but it's probably cheaper to adapt to C with the rest of the world.

Give me a bit more information and I'll be glad to help you do a more thorough diagnosis of the inaccuracy.

Barrie
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  #15  
Old 03-12-2001, 05:50 PM
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Hi Barrie,
Damn, I didn't sink it when I installed it, but I have 4 others in the sample package from Fenwal. I located it through the bumper, actually behind the front license place for protection. I believe it would be a lot smarter to relocate it on a standoff behind the bumper so it isn't touching anything and has good airflow. I'll try that tomorrow and let you know the accuracy. I can easily live with C, I thought there might have been a switch somewhere to trigger between the two measurements. Thanks for your help. Most appreciated!

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'76 240D-Sold
'78 240D-Sold
'85 300 SD, 165K-Sold
'88 300 TE, 165K-Sold
'64 Porsche 356C Cabriolet- under restoration
'86 560SL 124K Miles-Sold
'94 320E Wagon, 74K Miles-128K Miles JUNKED
'06 E350 Wagon, 84K Miles
07 SL550, 14K Miles
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