Shielding a QL, issues and questions.

[vanpeebles]

I'm going to have a go at shielding a QL case(due to problems with screen corruption) with some copper foil. Would the foil need to be grounded? If so where?

I've read old Quanta issues that poor shielding was a common problem in the past and sometimes people used paint inside the cases? Also what did the US Samsung model look like inside as I believe that was shielded?

Ta!

[dex]

European (German) Samsung QLs were sprayed inside with metal silver color, and there were small metal plates grounded on the main board with contact to the inner side of the case.

[vanpeebles]

Have you got any pics? Where are the grounding points on the board?

[Mr_Navigator]

In electronic terms most shielding is always connected to the zero volt line, If memory serves me correctly, split supplies such as +5 and -5 volt systems, +12 and -12 systems will have a 'ground' at 0 volts.

Single supplies in normally every case (and this should include the QL) that have a 3 pin voltage regulator, such as the 7805 (just in front of the microdrives on a heat sink), would be connected as follows:
Pin In – raw input voltage
Pin Out – regulated output voltage
Pin GND – connects to ‘0’ volts hence Ground and also shield

Diagram here http://www.national.com/images/pf/LM78M05/01048409.pdf
On most circuit diagrams general practice would be to have the ground connection as the most expanse of copper that you see, however it is not always the case.
If you trace the GND pin on the regulator to some point where you can attach a cable, or alternatively the black cable indicated here on the underside of the keyboard https://picasaweb.google.com/1087615291 ... 6513300162 this can be your connection to the shield that you put within the QL case, however it must not touch any other electrical connection, as this will short out and cause damage to your QL.

Alternatively you could run a cable from your shield connection to the big shiny metal case of the RF modulator. I will try and post an image later.

I am doing this from work without actually checking, so please if your not sure, refrain until confirmed by other people.

[dex]

Alternatively you could run a cable from your shield connection to the big shiny metal case of the RF modulator.

This way is it done in the case of german Samsung QL.
Modulator has a metal plate for connection with the cover piece (with keyboard) and is connected using a wire to the metal plate on the back of QL (where the Canon connectors are).
The metal surrounding the connectors is connected via another metal plate to the inner side of the bottom piece of case.

There is another metal plate next to the expansion connector door, which connects the inner shielding (it is fixed to the screw column) with the side of expansion card.

[vanpeebles]

Cheers everyone, I'll take some pics once the copper foil arrives and we can make a plan of action!

[Mr_Navigator]

Cheers everyone, I'll take some pics once the copper foil arrives and we can make a plan of action!

The mention of copper foil reminded me of when I was a lad (10/11 ish) many many years ago, my mum used to work at Plesseys (then an electronics company) during the evenings and one night brought home the end of a reel of copper foil. I had no idea whether it was 100% copper or not, but it looked shiny and was about 30mm wide.
We never had much money in those days as a family and as a child I used to get sixpence a week, which I spent going to Saturday morning pictures at the ABC cinema.

Anyhoo, I convinced my dad who was good with plywood, hardboard etc. (did this for a living at a place called the Wangey Works in Chadwell Heath, to make me a slightly raised plinth of around the size of a dining table, with a groove running around near the edge in the shape of a very large lazy B (a bit like the greek letter).

I stuck the copper foil across the groove all the way around and then cut it down the centre with my dads Stanley knife, saved up for a few months and bought myself the cheapest slot car and controller I could find, hey presto my home made Scalextric, I was over the moon.

[vanpeebles]

That's a great story, did it drive ok?

[Mr_Navigator]

That's a great story, did it drive ok?

Yes it did, however because of the size of the track, It couldn't go very fast without spinning off, the car was just too fast and also there are only so many laps you can complete on your own without any other competition to maintain the interest (I think it was more about building it than playing it which is why I think I went it to engineering when I left school). Eventually I moved on to other engineering things like the cellar with all the electrics for the house coming together on one board and some paint. But that's another story.

I just did a quick look around to see if I could find the orange racing car I bought, and here it is worth £45 now apparently.


http://www.scalextric-car.co.uk/Cars/C4 ... ra_LHS.jpg

I go on thinking that this might be an interesting project. A Scalextric circuit where one car was controlled by the QL, to which you race against. Some A/D needed I suppose, or has this already been done I wonder, anyone?

[QLvsJAGUAR]

European (German) Samsung QLs were sprayed inside with metal silver color, and there were small metal plates grounded on the main board with contact to the inner side of the case.

Here are some links to pictures of Samsung made QL's:

https://skydrive.live.com/?cid=c250d874 ... &sc=photos

https://skydrive.live.com/?cid=c250d874 ... &sc=photos

https://skydrive.live.com/?cid=c250d874 ... &sc=photos

https://skydrive.live.com/?cid=c250d874 ... &sc=photos

https://skydrive.live.com/?cid=c250d874 ... &sc=photos