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W210 1996 E320 Smoke Silver. [W124 1990 300CE Artic White - Sold].
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Discussion Starter · #1 · (Edited)
The history: because my instrument cluster (IC) had a few blind dots in the display of mileage, clock and outside temperature I tried to repair it with the result that all dots have gone dead. All the needles of the gauges for engine temperature, fuel, speed and rpm still worked fine.
I then replaced it with a used instrument cluster bought on ebay. The new one has no blind dots but all the needles of the gauges for engine temperature, fuel, speed and rpm are inactive, they do not move as you can see in the video at

http://s245.photobucket.com/albums/gg78/pham_doanh/Mercedes/?action=view&current=DefectiveInstrumentCluster.flv

which I recorded during a test drive.

I thought the new one might be defective regarding the dial needles and deployed my old one again because better to have all blind dots than no information on speed, engine temparature and fuel gauge.

To my great surprise they are now dead on the own one as well.

My guess is that the malfunction of the dials is now not from the cluster, since it fails on both clusters

I replaced all the related fuses #4, #6 and #7 from the fuse box under the hood.

Please tell me what could it be that no dial needle moves?
 

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W210 1996 E320 Smoke Silver. [W124 1990 300CE Artic White - Sold].
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814 Posts
Discussion Starter · #3 · (Edited)
Thanks Matt, where is the K40? :eek: :eek:

later: I opened the black box on pasenger side behind the coolant reservoir and see a big fuse with 40 Amp, is that the K40?
 

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1996 210.020
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It's in the module box under the hood, at the very front. It has five or six electrical connectors on it, and several fuses.
 

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W210 1996 E320 Smoke Silver. [W124 1990 300CE Artic White - Sold].
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Discussion Starter · #5 ·
I guess it is the one in the picture near the duo valve. It is the only one with fuses. I am going to check the fuses and report. Thanks for you patience!

 

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W210 1996 E320 Smoke Silver. [W124 1990 300CE Artic White - Sold].
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814 Posts
Discussion Starter · #6 · (Edited)
All fuses on that K40 module seem to be OK, nevertheless I changed them all and tapped and wiggled and pressed on all modules. Nothing changes. :( :(

Note: the needle for speed is not really dead but vibrates/oscillates a little at the resting (0 mph) position.

Could it be that the K40 module is defective?
 

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Perhaps the IC chip spoiled, if all connectors and fuses are checked. I remember one forum here talked about where to get the aftermarket chip (and which one), and you can change it yourself.
 

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W210 1996 E320 Smoke Silver. [W124 1990 300CE Artic White - Sold].
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814 Posts
Discussion Starter · #8 ·
Perhaps the IC chip spoiled, if all connectors and fuses are checked. I remember one forum here talked about where to get the aftermarket chip (and which one), and you can change it yourself.
From EPC (elec. part catalog) I see the module has part # 2105400272 but it is not further broken down, so that no IC chip is listed.
 

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I don't know if a defective K40 module can just kill your gauges, so I have to consider it a possibility.

Considering that your car is a '96, is the engine wiring harness original? That's another possibility.
 

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W210 1996 E320 Smoke Silver. [W124 1990 300CE Artic White - Sold].
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Discussion Starter · #10 · (Edited)
The wiring harness looks very good, not britle or damaged at any visible part.

The problem with the possibly defective K40 relay unit is that it is only my vague guess, and can only be answered with replacing it. But when my guess is wrong it is a waste of money and time. :( :(
 

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I opened mine up and resoldered the connections. But if yours is good to begin with, that could make it bad.

I would open it up and inspect it with a strong lamp and magnifying glass.

Disconnect the battery before unplugging the connections to the K40 module.
 

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W210 1996 E320 Smoke Silver. [W124 1990 300CE Artic White - Sold].
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814 Posts
Discussion Starter · #12 ·
Matt, do you mean the connections at the five connectors? or something inside the module?
 

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I mean inside. Yours looks to be about the same as mine (I have a diesel). The bottom shell comes off of the top plate. Inside, there is a circuit board with several relays, and large metal bars going to the pins on top. The connections on that board crack; I could see the cracks on mine, but only with a strong lamp and a magnifier.
 

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W210 1996 E320 Smoke Silver. [W124 1990 300CE Artic White - Sold].
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Discussion Starter · #14 ·
Matt, I think I screwed up again. I opened up the module and found scratches on the circuit board, inflicted by myself when prying up the module with a screw-driver - no pun intended.

I think I have the talent to make things worse when trying to repair them :( :(





What is the English expression for it, repairing something and making it worse?
The German have a nice word "verbessschlimmern" from "verbessern" = making thing better + "verschlimmern" = making thing worse.
 

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I doubt that you hurt anything. Inspect the scratches to ensure that they don't go all the way through the copper.

It's all those solder connections in the second picture that also need inspection. If there is a crack, it will appear as a circle around the center conductor.
 

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Discussion Starter · #16 · (Edited)
The scratches seems to be light and on the surface only. The connections are good as far as I can see. Am I out of option here?

here the circuit board again in higher resolution and cleaned:

 

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Discussion Starter · #17 · (Edited)
New development: having seen that nothing to be done with the Relay unit K40 I re-assembled and put it back with all the connectors and fuses. Then started the engine just for fun and lo and behold all needles came to life except for speed because the car did not move. Engine temparature went to 40, fuel gauge to almost full (I filled up 30 miles ago) and rmp went up when I pressed the gas pedal.

I was just about to yoohoo and hooray then wanted to be sure, shut down the engine and restarted ...

The dial needles are all dead again and again after another and another trials.
There might be something like loose contact, since the K40 and the cluster itself work fine, but what?

Help! Help! Help! I'd appreciate all comments!
 

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If there are cracks, I would not be able to tell by the picture. You need a magnifier to see them.

If the K40 is at fault, removing and replacing it could cause a broken contact to make again, reviving your needles. I suspect that it is.
 

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Discussion Starter · #19 ·
The game "on gain - off again" has been plyaed on me another two times since the afternoon without me touching the K40.

I am going to resolder all connectors on the circuit board to see if it is the cause.
 

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2004 E320 4matic Cubanite Silver, 1989 560SL Black Pearl Met.
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Resistors on the board?

I don't know if this has anything to do with your problem but looking at the picture of the solder side of the board it looks like some solder is missing from where the resistors are soldered on. I added some red circles to the areas that I would question. Also I work with electronic controls on spas and I know that those little relays can go bad but still look good.
 

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