vendredi 8 juin 2012

Indivision AGA MKII : How I got rid of my glitches

The indivision AGA MKII is a flicker fixer for Amiga 1200/4000/CD32.

Some new drivers have been coded for this board allowing the Amiga to reach some incredible resolution such as 720P. As we have never experienced those high resolution before the release of those drivers [Lisa (the AGA chipset) is pushed to its limits], it appears that some motherboards are showing some glitches.

I own 2 different Amiga 1200 boards (Rev 1D4 and Rev 1A).

Here is my experience with those new drivers.

The Amiga hardware is very old (20 YO), so it’s important to say that my 2 boards are recaped (capacitors changed) and that I use a recent PC PSU.

So I started with the Amiga 1200 Rev 1D4 with a Blizzard PPC accelerator (68060 at 50Mhz and 128MB of Fast Ram).

Here is the result :

You can notice the horizontal stripes and some glitches on the icons etc.
The first workaround I found, is software and it was using «fblit».

Some Amiga users have reported glitches before me and as «solder-Junkie» I was looking for the right Hardware fix for my issue.

The first thing was to add a 1K resistor like Jens Schoenfeld said:

Which I did...

But I had more glitches than before. The software workaround was still working.

Watch out: It seems that this fix is needed if you have vertical stripes (not my case).

I decided to keep it for now and try some new advices.

Jens Schoenfeld said : «Check E127R (might have to be replaced with a ferrite) and E127C (might have to be removed), but also the usual suspects E123C and E125C that may have to be removed for proper accelerator operation.»

Which I did :

But now the software workaround isn’t working anymore.

So I have decided to remove the 1K resistor (then fblit was efficient again), and leave the board as this for the moment. So at this stage it was a total failure !
>>So I decided to move on and I took the Amiga 1200 Rev 1.A motherboard.

This board was unmodified (only recaped), I put the Blizzard PPC with the 128MB of RAM on it and so the Indivision AGA MkII.

The result was exactly the same (same as my first video).

I was sounding weird to me. Two different boards showing exactly the same glitches.
I would have accepted it I had a different result as Amiga users were reporting different kind of glitches.

So I let the Amiga like that for the moment for doing something I wanted to do since a long time ago : upgrading my Blizzard 1260 with a 68060RC50 (71E41J). This CPU was also the one socketed on my Blizzard PPC.

And of course, when you finish this kind of work, you want to test if it works. So I took the 128MB I used before (on the Blizzard PPC) and put the Blizzard 1260@66MHz on the Amiga 1200 Rev 1.A.

The Amiga was starting, and BINGO...


Interesting eh? I let the Amiga runing 9 hours without having any crash/glitches.
Well...Let’s try with the Rev 1D4 (remember, I kept the board modded).

So, this is how I got rid of my glitches. I seems that the Blizzard 1260 is a pretty good accelerator that works with all kind of board revision without putting the solder iron on the Amiga.
Any doubts about it ? Well... One of the only video that has been posted so far without glitches has been posted by Fitzsteve and...What did he used ? A blizzard 1260@75Mhz.

My advice is : Install your own minimal workbench environment, put the monitor driver and try without the accelerator. Then report.

Now, lolof/EAB has reported glitches after 30 minutes of MP3 with AmigaAMP in 1024x768/64 colours with his Blizzard 1260@66Mhz on his 1D4 rev... Well here is a video in 720P/128 Colours playing mp3 for 45 Minutes without glitches...

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