A1200 - Display too bright

[alexh]

I edited my post to include pin 14 also

I was also thinking about the resistor values and voltage levels.

You want 9-12v on PIN 8 and 1-3v on PIN 16?

My ohms law might be a little rusty but surely to generate them both from 12v you need the larger resistor on the one you want to have the largest voltage drop? No? Does that mean they are the wrong way round?

It is quoted like you've said in 100's of places.

I must be thinking wrong. A long time since I did electrical power calculations.

[Rabbit80]

Originally Posted by alexh

I edited my post to include pin 14 also

I was also thinking about the resistor values and voltage levels.

You want 9-12v on PIN 8 and 1-3v on PIN 16?

My ohms law might be a little rusty but surely to generate them both from 12v you need the larger resistor on the one you want to have the largest voltage drop? No? Does that mean they are the wrong way round?

It is quoted like you've said in 100's of places.

I must be thinking wrong. A long time since I did electrical power calculations.

Me too - perhaps they are the wrong way round... Also does the wattage rating of the resistor matter?

No - my TV isnt auto switching either

The resistors seem to have no effect on the voltage (or very little effect)

[prowler]

Hi Rabbit80,

Thanks to you and all other contributors for this compelling thread.

I also have a problem with my A1200 display, though not such a serious one. I've only ever used the TV as a display as I don't have a monitor for the Amiga. The picture 'jumps' every now and again as if losing the video signal momentarily, but there are no other symptoms which is why it's only a minor irritation.

When I first got the Amiga, my TV at that time would accept only an RF input, so I thought the trouble was with the built-in modulator. Then I got hold of an external RF modulator (from a PlayStation), and connected the composite output from the Amiga to it, but the problem didn't go away.

When I replaced my TV, the new one had composite and scart inputs, so now I connect the Amiga composite output to the TV via the same scart input used for the PS2 and the problem with the display continues...

I too would benefit from building an RGB to Scart cable to help find the source of my display problem. I think I have all the bits I need to do this, and I might be able to help you solve your problem if I am successful with this.

Thanks for posting your wiring diagram, but first I'll see if I have the authoritative information on this you've requested.

I'll be back...

[Edit] RGB to Scart pin connections are documented on the following pages:
http://pinouts.ru/VideoCables/AmigaScart_pinout.shtml
http://www.allpinouts.org/index.php/...to_SCART_Cable

[Rabbit80]

I'm starting to think this is not voltage related

I have put a pot in (on Gnd and pin 23 - 5v) to regulate voltage and have tried all values from 1-3 volts without success

With this configuration it is possible to adjust the voltage from 0 - 5 volts going to scart 16 but I still get nothing.

On the plus side - My TV is now switching channels automatically after changing the 150 Ohm for the 1K

I have also wired pin 14 scart to Gnd and switched pins 17 & 18 on scart so I now go 19 (Amiga) - 18 (Scart)

I'm out of ideas now

[Rabbit80]

I'm almost sure it would be easier to repair the 1200 - what could be the cause of the troubles?

[prowler]

@Rabbit80:

Have a look at the links I've edited into my last post.

I think I'm going to build my cable according to those specs.

I'll let you know how I get on (probably tomorrow)...

[alexh]

Originally Posted by prowler

[Edit] RGB to Scart pin connections are documented on the following pages:
http://pinouts.ru/VideoCables/AmigaScart_pinout.shtml
http://www.allpinouts.org/index.php/...to_SCART_Cable

Both of which are not exactly correct.

[prowler]

Originally Posted by alexh

Both of which are not exactly correct.

What's the problem with these pin connections, alexh, apart from Scart pins 21 (the shield) and pin14 ?

[Rabbit80]

Aside from the fact I have wired each of the colour gnd signals seperately and the resistors - this looks identical to mine!

Edit: Which still does not work

[alexh]

Originally Posted by prowler

What's the problem with these pin connections, alexh, apart from Scart pins 21 (the shield) and pin14 ?

They do not go into enough detail about all the missing ground connections. It might work it might not. Especially on LCD TV's.

Originally Posted by Rabbit80

Edit: Which still does not work

Is it worth putting resistors on the RGB lines? The Amiga is known to put higher than normal voltages on it's RGB outputs. Most TV's do not mind but perhaps yours has over-current protection?

[alexh]

http://us2.aminet.net/docs/hard/AMIG...T-RGBcable.jpg

Amiga - SCART
23 (5v) ---> 16

Might be worth trying?

Another thread worth a look at:

http://eab.abime.net/showthread.php?t=37795

[Rabbit80]

I think I'm just going to get an A520 and take composite from it - it will be easier for now!!!

What values of resistor would you suggest on the RGB lines? I'll keep working on it but I have little faith!

[DDNI]

Perhaps this non amiga specific page will help you.
http://www.idiots.org.uk/vga_rgb_scart/index.html

[alexh]

Originally Posted by DDNI

Perhaps this non amiga specific page will help you.
http://www.idiots.org.uk/vga_rgb_scart/index.html

That page has the common mistake that has circulated around the internet. It's not their fault the same information is replicated almost everywhere. (Perhaps a previous version of the spec in the early 80's?)

It states pin 18 is "Blanking ground" and it is not. Blanking gnd is pin 14. Check out one of the SCART specifications (IEC 60933 or EN 50049-1) to be sure.

[Rabbit80]

So - where exactly on the Amiga should I take pin 14 scart from?

[prowler]

You know, if we ever crack this business of an Amiga RGB to Scart connection, we shall be the first EAB users to do so...

[alexh]

I think when TV's were CRT it did not matter if your cable was wired 100% correctly or not.

[alexh]

Originally Posted by Rabbit80

So - where exactly on the Amiga should I take pin 14 scart from?

Any GND? I would be amazed if it is not a common GND on the Amiga side.

[Rabbit80]

Originally Posted by alexh

Any GND? I would be amazed if it is not a common GND on the Amiga side.

Maybe its just my TV

Has anyone in Yorkshire got an A520 i can borrow for a while (I've got one ordered but I'm having to wait for a CC statement as I tried to pay with PPPay and I need a statement before I can verify my card )

[DDNI]

I have one you can have for p&P