Be Excellent To Each Other

As some of you might know a few weeks ago I ordered an lead to take an Amiga to an LCD via a SCART socket. While these work fine on normal TV's, many users report problems with LCD's. The official solution (including from the people who sell the leads) was to use a CRT instead as they would give a better picture.

But one Amiga fan didn't take this lying down. Why did LCD's play up? Why were my whites shimmering? As someone who works with video all day long I know its perfectly possible to have voltages that are so high they cause problems. But I was assured that everything the Amiga outputted was within spec. Hmmm.

After some testing with a multimeter I found the voltage on pin 20 of the SCART was quite high. I ordered a big pack of resistors and just spent an hour fiddling with various values.

In short I've found that if you wire a 220 Ohm resistor to pin 20 of the SCART the shimmering white problem goes away.

Now the picture is still not rock solid clear like the Dreamcast or Megadrive but I suspect there may be other problems with the Amigas output that need taming.

But for the time being, if you are an Amiga fan with an LCD and your piccy is looking shit, try a 220 Ohm resistor on pin 20.


[nb] This is quite separate to the switching issue which my lead already had a resistor fitted for.

You should spread this around the Amiga newsgroups.

Good work.

And start selling special Amiga to LCD cables.

http://eab.abime.net/showthread.php?t=36602
That guy agrees.

I saw a video of some dude who had modified his amiga to output VGA. I remember him saying that the standard RGB looked like shit on whatever screen he was using. He just opened up the amiga, tapped into the RGB lines and fed them into a convter board, I think.

Even though I haven't tested my Scart cable yet, I'm sure I'll have the same problem. However I am a cable and soldering inadequate.

No one saying "get a 360" yet?

Get an A1200.

Really really easy. Trust me, I'm crap.

Simply heat the pin you are removing on the back of the SCART. This will loosen the cable you need to remove. Cut the resistor to size and tin each end. Heat pin on SCART pressing one end of the resistor against it (doesn't matter which end). Then just solder the other end of the resistor to the wire.

The key is just trimming the resistor to size. If you get it wrong no worries as resistors usually come in big boxes for only a few quid. I got a multipack of 480 for about a fiver!

A cretin can do it.

I think it's just the sync level that's a problem. Whatever they've actually used for the sync, it's not at composite sync levels.

You are right in saying there are problems with the Amigas output. The guy who sells the leads insists everything is in spec, and while it might be I actually think the RGB levels (and sound levels come to that) are high. But I'll be fucked if I'm wiring resistors to every pin. The black level is certainly elevated. It looks akin to NTSC black displayed on a PAL monitor.

But now the shimmering has gone at least I can enjoy some Amiga gaming in reasonable quality. Not quite the rock solid pin sharp quality of my Phillips CRT monitor but 1000 times better than composite!

I'm a hamfisted oaf when it comes to soldering so not possible. But if anyone is considering do the mod themselves, if I can do it then so can you!

Although soldering irons and holders are great for pretending you are a member of the Liberator crew from Blakes 7.

That was the amiga that I had, back in the day.

Might be a bad idea to post anything related to 'problems with Amigas' on an Amiga forum, if the 'Amiga owner' stereotype is anything to go by.

My 1200 packed up. The AGA chipset decided, one day, that it was an AA chipset and refused to remember how it ran any 1200 specific games. My 600 is still in the atic and I'm loathed to throw it out so this LCD solution might be the start of something good. Top work.

Y'know, there's something a bit odd here. I remember connecting my A1200 directly to an SVGA monitor, and the problem there was the signals being too weak, so the picture was very dark. Made a buffer circuit and all was well.

If I had to guess I'd say the signal voltage is too high AND there's too much impedance in the output. So the effect you get varies depending on what you hook up to it - some CRT monitors are clearly fine, but a modern LCD monitor requires no current as it's not actually driving anything, so the levels aren't attenuated and appear too high.

Either that or it varies from Amiga to Amiga, which wouldn't surprise me in the least.

I thought AA = AGA? Just different names for the same thing. Presumably the AGA was coined to sound like VGA.

AGA stood for Advanced Graphics Awesomeness, silly.

Anyway, when I saw the topic I thought JC was involved: Amiga fans with LEDs. The horror.

Arnie Goes Apeshit

Always Gaping Arseholes

Auntie Groping Anus

The worst Auntie of them all.

SCART is not VGA. VGA requires buffers to drive the signal. You can't plug a DVD player directly into a VGA monitor the same way you can't plug and Amiga in. You can't directly plug VGA into SCART even if you scan low enough. It's Apples and Oranges. An Amiga will always need a convertor to help it.

As for SCART, the specs are the same for LCD and CRT. The difference is the analogue circuits in a CRT have alot more "give" in them. At worst you'll just end up overdriving the tube and it'll break, at best you might just get a very high pitched whistling noise when it displays white. They'll be lots of tolerance either way

But LCD's have to perform a analogue to digital conversion. Their A/D circuits will have a little "give" in them, probably clipping whites etc, but push them too far and they get confused. Which is what was happening with the sync.

Basically whereas CRT's will let you bodge a signal into them by hook or by crook, because the LCD's have to do an A/D conversion they tend to get more uppity.

Ah, I assumed RGB was RGB. But that explains it.

CRT sets will have a set of buffers with the gain connected to the "brightness" control for a start, so that helps.

I wonder if some LCD TVs cope with this better than others. Anyway, you found a workable solution...

what did the cd32 output? Rf or composite i assume

Both. And S-Video.

RF, S-Video and composite (from memory).

I've said it so many times but when Amstrad stuck a full RGB SCART socket on the GX4000, it was the most logical and well thought out inclusion of a socket on a computer/console ever. No proprietary leads, just plug and play. So why the fucking fuck did everyone else find it so difficult?

When I had the multimetre across the RGB pins, I did note they were quite low. But the TV's will have an AGC to cope with this. I suspect this could also be contributing to some of the other artefacts I can see (increasing gain will increase noise).

Both LCD's in the house reacted the same way to the Amiga without the resistor. But they are both Samsungs.

Oh, I agree with that. It's disgraceful that most consoles have required some proprietary lead (which are counterproductive for console manufacturers anyway, as most people end up with much cheaper third party leads). Thank fuck for HDMI, I say.

(The earliest Japanese model of the Sony PlayStation had direct outputs for S-Video and composite, but not RGB SCART, incidentally. I remember early adopters with imported PSes but not modern enough TVs weren't happy about that.)

My amiga's RF and composite outputs are both rather pink in colour for some reason.

Referring back to the original problem, and excuse me if this is a bit of a thick suggestion, but couldn't one tame the signal by routing it through some sort of SCART switching box?

Lol!

This is how I diagnosed the initial problem. But a SCART switching box has all sorts of side effects. For example the Amiga causes all sorts of issues for anything else plugged into the box. If your Dreamcast is plugged into the box then the Amiga kicks out so much voltage it will power up the fan. Not good!

You also attenuate signals that you don't want to attenuate. Whites become less white for example. The elegant solution is to just reduce the signals you need.

Through the mists of time I am fairly sure that there are inconsistencies in output between different batches of A1200s based on cost cutting and who actually manufactured them.

Mines a very early one. Lots of zeros in the serial number. We're talking the first batch that went on sale for Xmas 1992.

I'm surprised it still works. I went through about 3 A1200 motherboards which developed random, weird faults. I put this down to the cheap electrolytic capacitors drying up.