Heated screen help

[techbod]

Today I took the screen off the car and out of the surround and had a good look around. I assume mine is a standard CC screen - this is how mine is put together anyway. Each of the +ve and gnd wires has a short piece of metal at the end, almost blade like, which connects to the main piece of conductive foil that runs along the bottom of the screen.

 

The screen is made of two parts of glass with the heater element sandwiched between. The inside edge of each piece must be bevelled a certain amount since there is quite a thick bead of silicon between the two panes (which I'm guessing is how the pieces are held together?)

 

Looking at the internal heater wiring , the conductive element that runs along the bottom has a gap in the middle - it has to otherwise it would effectively be a short between the +ve and gnd wires. So in effect there are two separate grids wired in series, one on each side of the screen, each with approx 145 parallel elements.

 

At first I thought I might be lucky since one of the points the wires joined the foil was badly corroded and might be the cause of the extra resistance. However, poking the meter probes onto each end of the conductive foil showed the resistance was still in the order of 30 ohms - still to high. The way the two bits of glass are stuck together means it is possible to push a needle into the silicon and make contact with the top run of foil. That meant I spent a bit of time trying to measure the resistance of each of the 'groups' trying to work out if one was ok and it was just one side that had failed, but they both seem to have a more or less equal (and too high) resistance.

 

So thats it really. I found no obvious reason as to why some of the elements have failed have concluded that the high resistance is in the heater grid itself and not external wiring, and so better start looking around for another heated screen. Still as I'm getting to know how my 7 works at a good rate of knots which is no bad thing

 

cheers

 

 

Edited by - techbod on 25 Nov 2006 19:29:13