Video breakup

I have made a quite nifty VGA adapter for my A1200 using two pinout diagrams and a bit of soldering, however it does not hve any fancy chip-work in, which some people seem to think it needs.

Anyway, I have a VGA monitor hooked up to it and it seems to work OK for a wh8ilke under workbench then, usually when I open a menu, the screen starts showing artifacts. I have 2 theroies regarding this, as the artifacts seem to stay until a reboot. One is there is something I am running that is causing application memory to invade the gfx memory (operating on 2MB chip RAM alone - trying to resolve this but it's going to cost me) and corrupting the screen memory, which uses a lot of RAM as it's 640x480x16cols. The other is that my wiring i flakey. I doin't think it is, I used a nice shielded monitor lead for most of the cable run and kept the bare wire length down to about 2", and the signmal has no capacitance (red: shadows) on, it's really crisp. It's all in a little box too so it's not shorting on anything.

This isn't a biggy, it's just annoying as mit makes my wallpaper flash (it inverts it's colours then flips back every sop often at random) and can lead to me dropping everything I'm doing an rebooting.

[pteppic]

I did the same, built a VGA adapter without using the chip.  

It worked fine for 3 or 4 hours then I got a big blue puff of smoke from the back of my A1200 (before I towered it) which fried my video out port.  Since then my motherboard can only output video on the rgb or composite ports, can't even use the video port to hook up to a scart TV as I used to.
Fortunatly there was no other serious damage and now I have a graphics card anyway.

In any case I suggest you buy a proper vga adapter or build one with the chip for safety.

Pteppic

pteppic wrote:
I did the same, built a VGA adapter without using the chip.  

It worked fine for 3 or 4 hours then I got a big blue puff of smoke from the back of my A1200 (before I towered it) which fried my video out port.  Since then my motherboard can only output video on the rgb or composite ports, can't even use the video port to hook up to a scart TV as I used to.
Fortunatly there was no other serious damage and now I have a graphics card anyway.

In any case I suggest you buy a proper vga adapter or build one with the chip for safety.

Pteppic

Erm, there is no logical reason why it'd do this, except for one, which I ran into (nearly gave em a bloody heart attack too!). Because of the ability to hang a genlock on the back of an A1200 (yet another of the never-say-die expansions) the video port has 4 extra pin that pose perhaps the most danger known to your Amiga. These are at one end of the Video connactor and are '+5V, +12V' and 2 grounds. These are the power pins that powered genlock boxes and SHOULD BE AVOIDED AT AL COST, unless you know exactly what loads you are putting on them! They seem perfectly ok if left alone, until you short them by accident. I did this testing my adapter, and the Amiga went off. I tried the power, nothing. I tried the C= PSU (instead of my AT box), still nothing. I was starting to sweat by now! :-o I left it a few minutes and it eventually woke up and has been fine since.

My guess is that your adapter may have shorted these (did you wire up all 23 pins?) and lead to the connector, solder or something getting extremely hot. This is one reason I quickly wrapped my project up in a platic box, and made doubly sure there was nothing touching those pins!

I could be wrong, but simply leading the video signal off to a VGA monitor would not stress any components, the system itself is perfectly able to drive a multiscan monitor at 31.5Khzx65Hz, as Commadore includes the drivers to do it in WB3.1, and, if you ONLY wire up the right lines, it shouldn't place any untoward strain on anything as the signal is passive (i.e. always there, cable or not cable).

Thankfully I don't think I damaged the video controller or any sub-system components of the Amiga, it seems to happily output PAL modes when I'm playing games.

[Damion]

Hey MacMiga, what version of the OS are you
running? I had some strange problems while
using the VGAonly patch found in 3.1. Nothing
serious, but there were always lines in the
screen that really degraded the picture quality.
This problem seemed to disappear with the VGAonly
patch in 3.5. Anyhow, good luck with your adapter,
it sounds like a fun (and brave!) project.

The 1200 is an excellent machine. It still surprises
me how well they perform, even completely unexpanded.

-D- wrote:
Hey MacMiga, what version of the OS are you
running? I had some strange problems while
using the VGAonly patch found in 3.1. Nothing
serious, but there were always lines in the
screen that really degraded the picture quality.

That spunds very like what I get. I get lines, usually after opening am menu. It really ruins what is otherwise a very crisp looking desktop. My dad suggested maybe the chip is overheating but if it went away in 3.5 then it must be a driver issue.

This problem seemed to disappear with the VGAonly
patch in 3.5. Anyhow, good luck with your adapter,
it sounds like a fun (and brave!) project.

The 1200 is an excellent machine. It still surprises
me how well they perform, even completely unexpanded.

It's not all that bad if you do it right, you just have to check, and then double check, the wiring is right for tyhe sake of your monitor and your Miggy.

I am quite surprised how well mine performs as  astock machine with only an IDEFix board with a 5GB 2.5" hard disk and a CD-ROM attached to it.  Running F1GP form the hard disk is great, much faster than a PC of 1992 standards was!