Amiga A1200 RGB & composite video problem solution!

[Anemos]

Anemos back in the lab...

I had an A1200 with severe display problems, flashing - distortion - unstable display, even blanking.

I have no idea why this problem appeared, but I managed to find a solution, that actually gives a much brighter and stable picture with vivid colors.

The solution was to add a small 3mm light-diode in the specific place that is shown in the picture below
(I have also tried several regular diodes with relatively good results, but none provided the same stability and brightness as the light-diode)
In 5th photo i have the upgrade with added capacitor for more stability.
I must stress that due to the nature of this problem, my solution might not have the same results as mine, still worths a try!
Make with your trial responsibility
(thanks to keropi for translate!)

The problem



in the lab



solution



Final screen! .. ;D

[Amiga1992]

This was posted before, I am trying to find out the thread, but I can't!
This is a nice pic tutorial anyway

But in the text you say you replace with a light diode (an LED??) but you show a CAP on the pics... the fix I've seen postred before certainly uses a CAP. Are you getting confused?

[keropi]

Akira, Anemos used BOTH a light-diode and a cap!

[Chain]

smd one will be better, as conventional diode can apply more force to those smd pads

[Amiga1992]

Why a light diode?
The soluiton provided a the other post ONLY replaces the cap.
Can anybody find this other thread I am mentioning? I can't.

[PowerPie5000]

I also would like to know why an LED?? though this is not the first time ive seen led's on a motherboard as my dell systems also have them on the motherboard but i'm not sure why? (never bothered finding out either)

[prowler]

Originally Posted by PowerPie5000

I also would like to know why an LED?? though this is not the first time ive seen led's on a motherboard as my dell systems also have them on the motherboard but i'm not sure why? (never bothered finding out either)

LEDs provide a very stable reference voltage in much the same way as a Zener diode, but a lower voltage, of course (~1.7V IIRC)

prowler

[Anemos]

Perhaps you did not occupy, the problem video he was serious,
I am not reported for the (flickfix).
And yes is LED, most of them is diodes also (Light emitting diodes & Photodiodes).

[Retrofan]

As there aren't photos now (it has been 3 years), I would like to know where the cap goes, and what cap. I've got a problem with the Rgb ad the Composite http://eab.abime.net/showthread.php?t=64675

Well, perhaps it is somewhere in his greek web...http://flashback-computing.com/

[prowler]

Originally Posted by Retrofan

As there aren't photos now (it has been 3 years), I would like to know where the cap goes, and what cap. I've got a problem with the Rgb ad the Composite http://eab.abime.net/showthread.php?t=64675

Hi Retrofan,

I have copies of the photos from Anemos' opening post except "The problem" and "Final screen".

I'll zip them up into an archive for you and upload them to The Zone.

[Retrofan]

Thanks a lot. I'll post them here later.

There is a photo in the link of "my problem" (Attachment 31874) and perhaps I am wrong and the 1uF 16volts is the cap, and it goes where it shows in the photo of the led, but the draw of the pins with different lenghts makes me think it's referred to the led... but I don't find a led 1uF 16v. ?¿

[prowler]

Originally Posted by Retrofan

Thanks a lot. I'll post them here later.

There is a photo in the link of "my problem" and perhaps I am wrong and the 1uF 16volts is the cap, and it goes where it shows in the photo of the led, but the draw of the pins with different lenghts makes me think it's referred to the led... but I don't find a led 1uF 16v. ?¿

Yes, that photo is one of those I have found. It shows an LED connected to two pads, but you must also insert a 1µF 16V capactor between one leg of the LED and another pad as shown

[Retrofan]

Ok, thanks. So the photo I've attached is the one only necessary.

But he talks about the cap as something to upgrade it. In my mobo after soldering a led it wasn't on, and it did nothing.

[prowler]

Originally Posted by Retrofan

Ok, thanks. So the photo I've attached is the one only necessary.

Yes, it looks like it.

Originally Posted by Retrofan

But he talks about the cap as something to upgrade it. In my mobo after soldering a led it wasn't on, and it did nothing.

The LED is a diode, so it must be inserted the right way round. Perhaps yours didn't light up because you had inserted it back-to-front. The addition of the capacitor sounds like a refinement, and I guess the fix should work without it.

[Retrofan]

Thanks, and I know you haven't made this solution, so you don't have all the answers.. I tried it first cutting the legs, later soldering it the way round and later I soldered another without cutting. None turn on... but I will try again.

Edit: Tried. It doesn't turn on. I've got 1.23 volts between both points. Is it enough?

Edit: No, it isn't enough. These are my leds: http://www.ebay.es/itm/30x-Yellow-3m...ht_2445wt_1247

"Forward Voltage (V) : 1.9 ~ 2.1." So, what led must I search?

Edit: Forget about it. One of the points where I've got to solder it, after so many solder-desolder has disappeared. Well, the Amiga works the same, so no problem with that.

Edit again: I haven't lost anything. The point to solder it goes to the same place that the one of the bottom left. I can try another led. But I must know which one.
These are the ones I've found less demanding: http://www.ebay.es/itm/320703695867?...84.m1439.l2649
, from 1.35 to 1.6v.

[gibs]

@Anemos can you attach the pictures ? thanks

[Anemos]

hey, how gone the links on first post? (also i cant edit)

Here gibs.

[Retrofan]

Gibs you are extremely lucky to ask and have him here (I think, and in 13 minutes)...

Anemos glad to have you here. Have you seen that I'm using your trick (I call it "Anemos' Revenge Trick" Lol...). But I've found, just as @Romps has told me that it's better to quit the chip D125: http://eab.abime.net/showthread.php?t=64675&page=2

EDIT: Jeje... Just like you have in your photo now . If I had it, it would have been faster to fix this.

BTW I'm using now just a led, and it looks fantastic I've been using the miggy now for 3 hours (remaping some images for 16 colors, that takes a while) without any problem. As you said in post 1:

Originally Posted by Anemos

...A solution, that actually gives a much brighter and stable picture with vivid colors.

Do I need to solder the 1uf 16v cap too?

Edit: How? Now it is a 47uF 16v that I need?

[Anemos]

hello retrofan, in this A1200 MB the fast history is..
On this A1200 board have make before this mod "screen flickering when accessing the floppy drive" http://img212.imageshack.us/img212/6...mya1200lg1.jpg
with a capacitor.. after month, suddenly the screen is going to darkness about 80%, and unstable..
I fix it with this mod.. and yes you need 0.47Uf cap, not 1uf, other value working but unstable..
Ps. any led 2.5v or 3v working well, i try any type of normal diode,but result is better with LED! (dunno why).

[Retrofan]

Originally Posted by Anemos

...I fix it with this mod.. and yes you need 0.47Uf cap, not 1uf, other value working but unstable...

When you say unstable do you mean that the image is unstable without it (because mine is perfect) or that it can happen like to your other mod and after a time it can lose bright and become with an unstable image?