Cobra alarm in Mercedes

Printed From: the12volt.com
Forum Name: Car Security and Convenience
Forum Discription: Car Alarms, Keyless Entries, Remote Starters, Immobilizer Bypasses, Sensors, Door Locks, Window Modules, Heated Mirrors, Heated Seats, etc.
URL: https://www.the12volt.com/installbay/forum_posts.asp?tid=12026
Printed Date: August 27, 2025 at 3:31 AM

Topic: Cobra alarm in Mercedes

Posted By: pentoman
Subject: Cobra alarm in Mercedes
Date Posted: April 10, 2003 at 9:06 AM

Hi,

I am trying to repair the cobra alarm (appears to be date 05.87!) in my Mercedes 190E. It works fine, but recently the range of the transmitter has reduced to just a couple of feet (despite new batteries), and after sitting 'armed' for a while, the transmitter won't appear to work at all. The alarm still goes off if triggered, and otherwise acts normally. I don't think it's a factory fitted unit.

Is there any kind of service manual i could find on the net ro help?

thanks

Replies:

Posted By: Car-Stuff
Date Posted: April 10, 2003 at 3:53 PM

Sounds like the problem is down to the receiver card within the control unit. If you open the unit, you may find a "trim pot" on the receiver card, you could try and tweek this to improve the range. You will likely also have a trim pot within the remote also.

It's not easy to set up without a scope. Other than that, treat yourself to a new system - you deserve it...

Nick

Posted By: pentoman
Date Posted: April 10, 2003 at 4:27 PM

Thanks for the reply...

Somewhat optimistically, i took the alarm apart - here's a pic of the alarm in pieces. Top is the siren, left in pink is the main circuit, and on the right in green a separate circuit that joins it with some pins (seen on the underside). The only wire going into this is an odd coaxial one, which runs through the wiring loom but is then coiled round itself and connects to nothing - the end is circled in yellow.

I wonder if this is perhaps the aerial/receiver for the transmitter, and should be unrolled?

posted_image

Posted By: draasch
Date Posted: April 10, 2003 at 7:36 PM

you can try to do that, or see if you have the tuning ports that was talked about before. i would start with the transmitter first. they take a beating sometimes...

-------------
Good Luck
David
Ace Security
813-376-9778
Tampa
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Posted By: pentoman
Date Posted: April 12, 2003 at 6:14 AM

Thanks all - It just required tuning of the transmitter!
The range is excellent now, and no longer drops off so badly that I can't disarm the alarm after it's been sat for a while

Thanks again
Russ

Posted By: Car-Stuff
Date Posted: April 12, 2003 at 1:32 PM

Glad you got it sorted.

Nick