Heated rear window - repair of elements

[AndrewSlater]

Has anybody got an experience of successfully repairing broken elements in a rear 911 screen?

I ask as I am about to refit the rear Sekurit screen from '74 911 and have found that all 19 elements are open circuit.

It looks to me like the elements have slowly been abraded away over the years with cleaning.

I guess the question is what is the possibility of making a successful repair to the screen and what techniques can be used.

I was going to try repair with the loaded silver paint but I am unsure whether this is really intended to bridge gaps or whether if used extensively it will perform the function of the missing element. Also this might become a labour of love in order to repair all 19 elements.

I think the fuse is 25A so am guessing each element needs to draw 0.5 - 1A.

As always any thoughts much appreciated.
Andrew

[AndrewSlater]

To start to answer my own question, I bought some of the silver loaded paint to see if I could make an effective repair to one of the elements.

The element I chose had two or three breaks in it, at each side from the edge but the middle half of the element had little or no metal content left.
So I masked off the entire element, and then used a fibre brush over the first inch or so at the edge to give the paint something to electrically adhere to.

I then painted the silver paint into the masked area across the entire length giving three coats of paint, allowing each layer 10-15mins to dry.

The resistance is slightly difficult to measure consistently, so I chose to run a 12V power supply across the element to see what current I could pull.
At 12V the element draws approximately 1/3A, so 4W.



If I can repeat this across the other 18 elements that would give me 76W ( or 6.3A total ) across the screen.

Does anyone know what the actual specification of the screen would be?
I'm guessing the screen would originally have drawn a little more current - but I am in the right ball park.

Have yet to remove the masking tape to check how clean I can make the lines and also don't know the durability of the paint, but this could be a solution ( albeit a labour of love ) - oh well only 18 lines to go !

[Joelipol]

I reckon you make a good business repairing these things if you were to figure it out. Keep going and post the results!

[tangerineT]

This looks really interesting chaps

My screen is worn away on the element,,probably due to heat in texas and cleaning

I'd be interested to know which products work !

Let me know as I'd like mine to work if possible

Thanks matthew

[AndrewSlater]

Thanks for the comments guys.

I must admit I got so far with this and decided I had spent too long and needed to move on.
I wasn't happy with the cosmetics of the screen so removed all the paint and fitted the screen as is.

However for the sake of helping others here are my thoughts.

I think the silver loaded paint can be used succesfully to repair short breaks in the elements.
I could repair a full length of element however with the following caveats.
Firstly in order to get the low resistance required I had to paint the lines slightly wider than original ( maybe 50% wider ).
Although I don't know the actual specification of a new screen I am guessing you need to pull at least 0.5A and preferably closer to 1A per element.
I also found that an element that was repaired one day would often degrade over a day or two as I think the silver loaded paint is not very robust.
The silver lines also don't look cosmetically great from either side.

If I was to take this further I think I would change over to using a silver loaded epoxy for durability.

I think the process would be to mask lines and paint first ( to get the cosmetics right from outside the glass - depending upon the colour of the epoxy ).
Then use silver loaded epoxy to reinstate the lines. Testing them one at a time ( 1 line - 1A, 2 lines 2A etc )
Then apply another coat of paint on top again to get the cosmetics correct.

I think the silver loaded epoxy is quite expensive and the masking process doesn't use it efficiently - so it may not be a cheap option.
Either way it is definitely a slow process, and I think my screen had 19 lines to repair.

Another thought I had was to embed a wire into each line as this would be more robust.
I notice you can buy wires that are used in vaping equipment that might be suitable and aren't very expensive.


If anyone makes any more progress on this I would be keen to hear - good luck.

[tangerineT]

Thanks Andrew

I had wondered how successful this could be ,, might just have to accept that my rear screen doesn't work

Oh well ,, it is over 40 just like me