Amiga A1200 boot screen red colored / red boot screen with RGB

samysplace

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Dec 21, 2015
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germany
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Hello everyone,

I have a Problem with my A1200:
The boot screen is colored red, as you can see in the pictures I added.
The thing is; this only happens when I connect it with the RGB cable to my Screen.
When I use the composite connection , the picture / boot screen shows up normally.

Does anyone knows this problem or has an Idea?
I would be really thankful for any advice :)

best regards sam

PS: The pictures are reverse for no reason :-/
 

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Hopefully it's a bad RGB cable.

Are you sure that you don't have the red and the blue switched?
 
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^^ thats what i thought, red / blue on cable.

if the blue was faulty it would show black not a screen of red right ??
 
Blue is not connected or the blue pin in the rgb port maybe pushed in..
 
Thanks for your comments.

The cable is definitely not broken , I tested it with two other amigas and the picture was fine.

The RGB Port looks fine too, I added a picture so that you can take a look.

@Rootboy, so you think that the colours could be swtched on the board ??
IMG_0555.JPGIMG_0554.JPG
 
Here is the a pic of the Video circuit, the Composite is working so the Video dac is good as is the Video encoder so check the components in the RGB circuit, here is also a PCB component finder http://amigapcb.org/

A1200 video.jpg
 
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Here is the a pic of the Video circuit, the Composite is working so the Video dac is good as is the Video encoder so check the components in the RGB circuit, here is also a PCB component finder http://amigapcb.org/

View attachment 115906

Check resistors R232A(Red Channel), R232B(Green Channel) and R232C(Blue Channel) as they should all be ~25 ohms
 
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Thanks @supaduper :)
I checked all the resistors ( R232 A/B/C and R231 A/B/C) and the three capacitors (C211,C212,C213) , they all seemed ok and had the proper values .

so from my understanding the only components that remain are the diodes.??

- - - Updated - - -

thanks all for your help, thanks @ptp170 I just checked them in this moment :)
 
Thanks @supaduper :)
I checked all the resistors ( R232 A/B/C and R231 A/B/C) and the three capacitors (C211,C212,C213) , they all seemed ok and had the proper values .

so from my understanding the only components that remain are the diodes.??

You are surely missing the blue channel for some reason. The background on the KS screen is normally purple which is red+blue.
If you make the Amiga show some full screen grey or white picture, then you should be able to measure approximately the same voltage on R, G and B. Do that on various points from the RGB connector towards the DAC and should should find the culprit. If all the resistors are good, then it could be a shorted diode as you write, so check D231B and R231C.

It could very well be a burnt track somewhere on the MB but then I would expect it to be visible. It could be located on the underside though.
 
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I can't see how it could be the diodes as (if faulty) they would pull the R, G or B signal low which would mean the blue signal going to the encoder (composite) would also be effected..

Actually, I've just noticed the signal from R232C goes through a ferrite bead E258R before it makes it to the port... I think the bead maybe fractured...

EDIT: Also just noticed that on the bottom of the board E258C which is a 47pF capacitor... if that's shorted it would also remove the blue signal
 
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Just to be on the save side, I replaced E258R , E258C and D231B that I took from another 1200 Board.

But the red picture remains :-/

- - - Updated - - -

Now I am a little bit confused... I decided to replace D321A as well, and for one second when I switched on the power button I received a purple color on the screen - than a short white flash - and then the red boot scree again.

Could it be, that some component damages the replaced parts??

In that case, I could replace anything, and it would`t make a difference :(
 
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