Display options and colour fault on Amiga 1200

[Dimlow]

first of all Hello to all, Years ago Iwas very into my Amiga 1200 and used to right Games in Amos and learnt to program in C on the Amiga until commodore when bust and i decided to Swap to the PC.

Well years later and with the wonders of EBay i purchased another Amiga 1200 witch of course worked for a while now the colour has stopped displaying on the TV. (The TV is fine) So i have purchased ( not arrived yet) an RGB scart lead for the Amiga in the hope that the RGB will work fine and that the problem is just with the modulator of the Amiga and not the Amiga its self. So the question is have i done the right thing, will i see colour again, if not then does anybody have a clue to how a go about checking the Amiga? I am well equipped with scopes and meters and can find my way around digital electronics quite well.

The next question for all you Amiga experts ( I was one once but my memory has failed me!) is what options are there for the Amiga 1200 for getting a better display resolution in Workbench? In the days i remember having to use 640 x 512 laced and putting up with the flicker on my TV screen. But with today's LCD TVs and monitors there must be some other option ? I guess i just got used to my 1920 x 1600 24" monitor!

Some specs on the Amiga so far
I have installed a CF card as a hard drive.
A Blizzard 1230/50Mhz 8MbRam with FPU has been ordered.
A Prism2 based wireless network card Ordered.
3.1 Roms have been ordered.

Something that surprised me about going back to work bench from my Q6600 3.3Ghz PC. THE AMIGA SEEMS MUCH MORE RESPONSIVE!!! Must be somthing to do with Windows Vista Bloat.

Also if you guys have some tips suggestions of OS and other software/ C compilers / etc etc. Id be grateful of them.

Oh Yes, i have searched for these answers on the forum but didn't really find the answers.
My claim to fame! I once got on the cover Disk of Amiga user international with my software for converting Texture Studio Texture files to Imagine Attribute files (ts-i is still on Aminet!). Also got my Imagine Object of a train on that same disk. I am also the author of DisCat(Lost forever i believe) Written in Amos and also published in the same mag i think.

Also as a special request does anybody have these magazines, with my stuff on, id really like to get a copy!

Regards
Gary

[Matt_H]

Hi, Gary. Welcome back.

You're well on your way to a fine system. The only thing I'd suggest would be some more RAM - any single-sided 72pin SIMM will do. These are all over eBay, some are even advertised as being Amiga-compatible, albeit, with a markup.

I have no idea about the color problem. Failing capacitors seems to be a common problem these days, so you might want to check those out, but I don't know if they're involved in video circuitry.

640x512 is the highest you can go on a TV. The Amiga's weird video modes are a big problem these days as not many devices can display them. A thing called a scandoubler will allow you to connect to a standard monitor, but these are irritatingly rare and expensive. Jens Schoenfeld is developing a new one (info isn't on the website), so that'll hopefully solve the "rare" problem. It also scandoubles a custom-written display mode (on Aminet) that allows 1024x768.

For higher resolutions, you'll need to move the Amiga into a tower case and add a busboard and graphics card. Or get a big-box Amiga and just add a graphics card.

Some LCD displays can handle the Amiga's 15KHz rate, but they also need to be able to handle PAL's 50Hz refresh. Many can't.

With a plain 23pin to 15pin adapter (carried by most Amiga dealers) you can use the DblPAL/DblNTSC and Multiscan screenmodes on a VGA monitor. You can't display regular PAL and NTSC with this arrangement, so it's useless for most games.

[Dimlow]

Thanks for that Matt, first question, why more Ram? i only had 2 chip and 4 fast on my old Amiga, 8 Mb seems plenty.

As for the colour problem i have found some circuit diagrams and it seems that there is a colour clock generator from a crystal that goes to the CXA114 chip, this chip generates the composite video signal in the Amiga, this is then fed to the modulator and the composite out. both the composite and modulator output go grey scale after about 3 minutes of running so i guess its that clock signal that is failing. but the good news is that as far as i can see the RGB output will not be effected by this, as this clock signal is not used in the RGB output. Yippe

I will look for the lost signal with my scope one day, but for now its not important!

I will definitely have to look into getting the Amiga on a VGA monitor, but i think for now the scan doubler is out of the question as they seem so rare and expensive. Surly there can't be much to them i will looking building something like this in the future when i have more time.

1024x768 looks good, got a link to the file? i couldn't fine much about it in aminet ( I'm currently downloading all of aminet!)

Isn't EBay Great! just ordered 2x32Mb 72 pin 60ns Simms for £2.00 , so 64Mb ram OK ?

Regards
Gary