Strange Central Locking Behaviour - Mercedes-Benz Forum
 
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post #1 of 7 (permalink) Old 10-07-2016, 06:32 AM Thread Starter
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Strange Central Locking Behaviour

I've been having an ongoing problem with the central locking ... sometimes it would lock from the driver's door, sometimes not. Quite by accident I've now established the following:

1. If I deadlock the boot while the drivers door is adjar, everything will lock except the drivers door (obviously a safety aspect);
2. If I then close and lock/unlock the drivers door, all doors and the fuel flap will lock, every time.
3. If I leave the drivers door adjar and lock/unlock the boot all doors except the drivers door will lock (as above).

The point is, if the drivers door is left adjar and closed after the boot is dead-locked (turned to the 3 o'clock position) the central locking works fine. However, if I simply lock the boot and then lock/unlock the closed drivers door the central locking may work, it may also leave all the doors, fuel flap and bootlid open and leave me with a situation where only the drivers door locks/unlocks.

Any ideas? It can't be the micro-switches as they obviously seem to work. I was thinking it may be the pump's on-board PC board, the pump is not running long enough every time to lock all doors? Oh, there's never been an issue unlocking all the LOCKED doors, but there is a problem locking all the UNLOCKED doors.

1992 W124 230E Auto, M102.982, 212,750 km / 132,968 miles, MBSA-built - CURRENT.
1985 W123 280E Auto, M110.988, 110,265km / 68,915 miles, MBSA-built - SOLD.
1985 W123 230E Manual, M102.982, 219,320 km / 137,075 miles, MBSA-built - SOLD!
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post #2 of 7 (permalink) Old 10-07-2016, 09:49 AM
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The pump died on my wife's car recently, I carefully took it apart and found...







in that last picture, those two leaf switches next to the little disks, I believe those act as vacuum pressure switches, and tell the box to stop pumping once the pressure is fully up or down.
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post #3 of 7 (permalink) Old 10-07-2016, 10:18 AM Thread Starter
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Originally Posted by LeftCoastGeek View Post
The pump died on my wife's car recently, I carefully took it apart and found...







in that last picture, those two leaf switches next to the little disks, I believe those act as vacuum pressure switches, and tell the box to stop pumping once the pressure is fully up or down.
The pics are excellent, thank you (I previously took my cover off, my circuit looks okay ... maybe I should go in for another look)!

Looking at your first pic it's obvious your resistors overheated, the question is why? If one looks to the right and slightly down it seems two of the three pins have lost their connection with the board (solder gone), this seems to be part of the magnetic coil switch. Did you have a leak, was the pump running longer than necessary, i.e. not switching off after a specific time, possibly leading to the overheating of the resistors? It seems the thick two-pin inputs provide the power, while the smaller three-pin (FTS, KDS, TS) provide the inputs from the micro-switches, these in turn then trigger the magnetic coil switches.

I'm no electrical engineer, maybe someone with an electronics background could shed more light on the circuit diagram and current flow.

1992 W124 230E Auto, M102.982, 212,750 km / 132,968 miles, MBSA-built - CURRENT.
1985 W123 280E Auto, M110.988, 110,265km / 68,915 miles, MBSA-built - SOLD.
1985 W123 230E Manual, M102.982, 219,320 km / 137,075 miles, MBSA-built - SOLD!
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post #4 of 7 (permalink) Old 10-07-2016, 10:39 AM
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Originally Posted by RSK_W123_230E View Post
The pics are excellent, thank you (I previously took my cover off, my circuit looks okay ... maybe I should go in for another look)!

Looking at your first pic it's obvious your resistors overheated, the question is why? If one looks to the right and slightly down it seems two of the three pins have lost their connection with the board (solder gone), this seems to be part of the magnetic coil switch. Did you have a leak, was the pump running longer than necessary, i.e. not switching off after a specific time, possibly leading to the overheating of the resistors? It seems the thick two-pin inputs provide the power, while the smaller three-pin (FTS, KDS, TS) provide the inputs from the micro-switches, these in turn then trigger the magnetic coil switches.

I'm no electrical engineer, maybe someone with an electronics background could shed more light on the circuit diagram and current flow.
I'm a bit of an electro-nerd, but I saw that charred PCB, and decided to get a remanufactured unit.

as far as run to long or what, I have no idea, its my wife's car and I only find out stuff is broken when I drive it, unless she remembers to tell me at 1am or something (which of course, I never remember the next day, oops, its all MY fault, hahahahah, ok, we've been married nearly 35 years now).


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post #5 of 7 (permalink) Old 10-07-2016, 12:14 PM
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I promise it's YOUR fault.... from a guy who's working on 41 yrs of marriage.
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post #6 of 7 (permalink) Old 10-07-2016, 12:58 PM
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I promise it's YOUR fault.... from a guy who's working on 41 yrs of marriage.
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