124 Immobiliser/alarm

[cross]

1993 220 E 170k miles with 2 fobs, handbook etc. Scorpion alarm I think
I have a fob as per attached photo (Having difficulty down loading the jpg. )The fob is oblong with 2 press pads at the top (right and left) the left activates the unklock function - top left hand corner is a tell tale that light red when the left button is pressed - top right hand corner is a recessed tiny screw (for adjustment I assume) there is a slide switch on the side which has 2 positions up/front (towards the buttons) and down/back (away from the press buttons) The switch is positioned at the "up" position

Yesterday after long time problem free usage the fob would not open the door - I resorted to a key opening and the alarm went off - I rushed for the spare fob and cancelled the alarm by pressing ( I think -the left hand and right hand buttons)- it was at 7.45 am and I was a little concerned for neighbours etc.
The spare fob works fine - opening and closing the car without problem.
The original will not however open the doors. I replaced the battery - thinking it might be flat - but even with a new battery the fob will not open the door.
The "bad" fob shows a red light when the button is pressed so I assume that power (with a new battery) is not a problem.
Does this fob need resetting - if so can anyone advise why, and how is this done ? Does it need replacing ?
Can anyone throw any light on this problem please - I have searched for other threads but have not found anything suitable.

 

[television]

You can check the IR beam by testing in front of a digital camera

 

[Dec]

Scorpion Alarm Fob.

1. Lock/Unlock
2. Panic button turns on siren.
3. Battery indicator.
4. Round key to turn ON/OFF alarm.
5. Tactile switch under both buttons.
6. 12v Battery.
7. Don’t know what this screw dose it could be a distance or radio frequency adjuster, best left alone.
8. 3 pin socket for factory programming.
9. Slide switch;
In one position it turns OFF alarm internal motion sensors and indicators flashes 2 times.
In opposite position it turns ON alarm internal motion sensors and indicators flashes 3 times.

Operates on radio signal no infrared.

In your case it could be a poor connection on the Tactile switch (5), examine closely with a magnifying glass and try operating the switch with the casing open and rubber button removed.

See also, as example… http://forums.mercedesclub.org.uk/showthread.php?t=26895

Dec

 

[cross]

scorpion alarm problem

Gentlemen,
Apologies for delay, was away for the weekend, many thanks foir your replies much appreciated.
Explanation of the fob very useful - thank you Dec
Have already opened the fob and tried the operation without the rubber button - I had assumed it was making correct contact as the red light lit when the button was pressed - but will have a much closer look front and back.
In the event that it looks OK - do you think I should assume the unit/fob is kaput and I need another one ?

 

[Dec]

For my part, I don’t know enough about that type of electronics to comment, Malcolm is the man for that.
Unless you can find a bad solder joint, there might be 4 legs to that switch, 2 to test the battery which seems to work o.k. and 2 to send the signal, maybe the are the problem, but that’s only guess work on my part.

I turned on my house radio to a VHF station and held my working alarm fob about 3mm from the antenna, every time I pressed the button I got an interference bleep on the radio reception.
What I don’t know is whether the switch being pressed and the Red light coming on is causing the interference OR the radio signal from the fob is causing the interference. You might try that just to see what happens.

Dec