Cobra alarm in Mercedes

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

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

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?

Thanks all - It just required tuning of the transmitter!

Thanks again

Glad you got it sorted.

Nick