1994 E320 Cabriolet Passenger Window Question - PeachParts Mercedes-Benz Forum

87tdwagen · #1 11-10-2014, 04:25 PM

Dear all:
I finally bit the bullet and got me a sweet low mile 1994 Cabriolet to add to the stables, a Polar white with parchment cladding, blue top and light grey interior. Rides like a dream, better than the S124 surprisingly given the shorter weelbase, but if feels like a 3 ton block of steel floating on a cloud

Anywho...I do have a rather unique "feature" that I'm not sure if was intended by the good engineers at MB. Seems as the passenger door window does not want to go down upon putting the keys in ign or starting the car, unless...

1. I repeat, take key completely out and then power pass window down before starting the car.
2. Use the Top-Down button and all windows go down and function normally.
3. Use the master key in the drivers door to operate full open, full close.
nope nary a problem.

Only when I get in the car and just want to lower the passenger window does it not work

I thought it may be the window switch contact, but when it does work in steps 1-3 above, it functions fine, up/down etc. so I ruled out the window switch as it does function.

So I assume my problem is with the brains, (I often get this comment) or some switch somewhere that is not letting the convenience control module know that all I want is my window to just open when I hit the switch... is this too much to ask??

Ideas?

A. Rosich · #2 11-11-2014, 08:24 PM

If you are sure the problem is not on the switch the it should definitely be the convinience module. W/A/S/C124s and W/V/C140s are famous for temperamental convinience modules, and the windows or the sunroof are always developing minds of their own. I would try to get a borrowed module from an independent tech and see if changing it cures your problem. If it does, then its time to buy a new one.

87tdwagen · #3 11-12-2014, 10:26 AM

Thanks A. Rosich
I'll take a look at the switch again and clean it or replace it with another known-good window switch to see if that works. Otherwise proceed as you suggested.

Funny name that Convenience Control, provides neither control nor convenience

87tdwagen · #4 11-13-2014, 06:03 PM

So I guess the electrical possessed sprirt of my E320, had decided to leave the passenger front window and jump to the passenger rear instead. Now my front works great

Although my rear now wont go back up

Yippie.
Given this random "feature" and a clicking convenience relaym, I also noticed that the original CCM also had the windows powered with the ignition off key out

I went to the pick-u-pull and got another CCM cheap, has a warranty swapped the two and. My windows do not have power with the key off, the convenience relay has also stopped clicking (proly the windows being hot) yet no difference with the RR window operation. The Parts unit was from a sedan, from what I read they are all supposedly interchangeable between the w124s and several W202 hence the 202 part numbers.

I used to be able to get around the issue with the all up/down feature from the convertible top switch and or the door lock, but neither of those functions work now on either CCM.

When running through the window switches I can hear all of the relays in the CCM click up/down except the right rear which only clicks down, but not up.

I had opened and looked at the parts yard CCM before installing it and it looked pristine, no signs of burning or corrosion. Now that that CCM is in the car, I also opened the original unit and guess what... looks fing pristine

Any ideas of how to test the unit or how I can restore use of my rear window?

87tdwagen · #5 11-14-2014, 02:41 PM

So I got the rear window to work, turned out to be a cold solder joint on the RR up regulator within the CCM even in the replacement CCM.

I looked over the original CCM and stopped counting after about 20 cold solder joints. Went through and proceeded to repair those but upon testing the unit again, my control relay (in the fuse box) was still clicking albeit not as badly as before. Pulled the CCM and will have a look for more bad solder joints.

Like several other relays and components from this period, MB must have been using bad solder or just a product of age, but bad solder joints seem to be a problem with many components. Rather than replace, have a look to see if you can spot them under magnification and repair rather than replace as even your replacement part will develop this issue.

Will post a final update if I can get my original CCM to work again as a spare since my replacement one is up to task now.

oldtrucker · #6 11-14-2014, 06:46 PM

I had a problem with the Blinker stopping on hot days and sitting in traffic.
If the convenience module is the same technology as it is with my 95 E320 Sedan, then there might be a good chance that the riveting on the plugin posts are corrosive underneath, not visible to the eye.
You, say you soldered lots of cold ones, I think they soldered them in a wave and had perhaps a bad batch of products produced.
If you can, check the rivets and resolder them using a drop of solder flux. The flux does normally clean the corrosion, making it a better, durable contact.
I am almost convinced that the rivets are the culprits!

87tdwagen · #7 11-14-2014, 07:40 PM

I found a few cold solder joints but mainly cracked joints right at the post, only visible with 10x magnification, it seems as most of the components are very durable but suffer from tired electrical connections that can be rejuvinated.

So are you talking about the rivets that mount/connect the bullet shaped male plug posts to the post legs leading to the PCB in the Convenience Control Module?
I still have my orig CCM out and apart, and am curious to find out more about you approach. Do you mean actually soldering the rivet heads to the post legs?

Like those circled in Red below?

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oldtrucker · #8 11-14-2014, 11:14 PM

Quote:

So are you talking about the rivets that mount/connect the bullet shaped male plug posts to the post legs leading to the PCB in the Convenience Control Module?
I still have my orig CCM out and apart, and am curious to find out more about you approach. Do you mean actually soldering the rivet heads to the post legs?

Yes, they can, over time get lame through vibration, contamination or even corrosion.
What happens in my opinion is, all or part of the above will add some resistance (over time) and when it comes to sensitive feedback circuitry, it may sense the wrong value because of that added resistance, intermittent contact or spikes or ?. In general an OP AMP input can be thrown off by just a few millivolts that drop across the connection post.That voltage doesn't show up on the input, therefore the input sees less voltage than expected. If for example the feedback is looking for current, converted into a voltage, e.g. the window motror (example 100mVDC expected) and gets only (example 80mVDC) (also electrical noise can play a significant role), it may simply not trigger the relay and nothing happens, because the circuit was designed to do that if someone puts a hand or finger into the moving part or simply a fail safe. The value measured, depends on what the designer was thinking at the time. There are too many ways to design something!
Mostly made of two different metals that change density with temperature, it could as well work in warm temperatures, but when the abient drops, it doesn't anymore or v.s.
Many people believe that the OVP is responsible for a lot of electrical problems, it might be worth to check it, that is tricky without an oscilloscope.

I didn't do any scientific testing on mine and all is only theory. But, since I soldered mine electrically solid, I have had no failure. Components (except 1960-70's CMOS) rarely ever fail. It's the PCB and other factors that cause failure.

It's a little bit of a pain since some of them may not be easily reached.
A drop of solder flux and simply solder them together with a hot iron and large tip. (Don't get too large or hot)
Don't want to mess around too long, not to melt the plastic.

Additional:
Actually, from your picture, I see that there is some sort of a Motorala MCU (Micro Control Unit) used, it may have a number of AD converter that sense the various places of interest. In the 90's they usually ran off 5VDC supply, meaning that the AD converter could as 10 Bit converter do (5VDC / 1024 = 4.88mV) per bit. In other words it could, in theory measure about 5mV changes. Practically, it is probably less accurate.
The two metal strip's below the red circle, are actually very low restance current sensors.
At the bottom of the image is a hybrid IC, standing upright. There is a number of rectifier diodes visible. These are probably used, as I call them "free wheeler" to protect the circuit from the large spikes that the relays produce, when switched.