A1200 RGB Video Problem

[darkwave]

Hi all,

I'm having some issues with the RGB output with my A1200. I bought an RGB cable for my A1200 so I could take advantage of the greater picture quality. Although the image does output, it is wavy, and the tv's 'No Signal' text ghosts up and down the image.

At first I figured this was maybe the tv or the cable, but recently I bought an A600 which works absolutely perfectly with the same setup. So then I bought another A1200, thinking it might be a dodgy RGB port. Same problem.

The one thing these A1200s have in common is that they are both revision 1d4 boards. Do you think the motherboard timing error could be affecting the RGB signal, causing it to output at a slightly different frequency from the A600?

Any help would be greatly appreciated!

[Zetr0]

have you tried the composite signal out from both the a1200's ?

[darkwave]

It works fine through the composite cable; no rolling whatsoever. Unless you mean the RGB port outputs a composite signal through scart as well, in which case I don't think my scart cable is wired for composite as I get no picture when plugged into my non-rgb scart socket.

[rkauer]

Originally Posted by darkwave

It works fine through the composite cable; no rolling whatsoever. Unless you mean the RGB port outputs a composite signal through scart as well, in which case I don't think my scart cable is wired for composite as I get no picture when plugged into my non-rgb scart socket.

I'm not an expert in SCART, hence there not a single SCART TV in this side of the pond.

But for what I read, the SCART connector can be used for RGsB, RGB-S and other things. So a simple, naive question: those A1200 are NTSC versions? AFAIR, PAL TV systems don't sync very well in 60Hz.

And other probably culprit: what PSU you are using with the 1200? The bog standard? If so, try a better PSU, hacking one from an AT/ATX one or even a Goliath (if you find one...).

[darkwave]

Well it's not the PSU as I've tested this with the standard A1200 one, an A500 one and a Goliath. They're both PAL A1200s, but then so is the A600, so I don't know why they would be any different.

It's really bugging me. I need to find out if the timing fix affects any of the graphics chips at all, which I presume may in turn affect the overall output sync.
I'm just guessing though, I'm fed up with having to use composite.

[TheCorfiot]

2 Questions,

Is the RGB output syncing, V+H, If it's jumpy, try feeding the composite output from the A1200 as the sync into the RGB, I had to do this with my A1000 years ago. Check if there is a resistor in line on this signal within the cable.

Is the Fast Blanking Voltage for RGB sufficient, again check if there is a resistor in the Scart cable passing from +12 V to FB on the Scart input.

The Signals & voltages being output must be fine as both A1200 can't be faulty, My one A1200 is a 1D4 & RGB output is fine.

Do suspect the cable, just because the A600 works is not really a good basis to prove it's OK as voltage levels maybe slightly different, ie within tolerence levels between the A1200 & the A600.

If you can get another cable to test that would be the best.
Download schems for the cable & compare it with the one you are using.

[twizzle]

i have had the same problem, i min its ok and the next the image is all wavey.
if i wiggle the scart connector around its ok again.
it turned out to be a few dry solder joints on mine.

[Zetr0]

very interesting.....

very interesting indeed.... why work on the a600 but no either of the a1200's ??

hmmmmm

[rkauer]

Originally Posted by Zetr0

very interesting.....

very interesting indeed.... why work on the a600 but no either of the a1200's ??

hmmmmm

Because the video circuit is slightly different?

[Zetr0]

@RK

my friend i thought that but the A600 is virtually identical to the a1200... the both use the same Sony CXA1145 encoder chip. the both have identical pin outs on the 23 pin video port.

there could be a current differential, the a600 uses less power than an a1200 .... hmmm i wonder if that scart lead resistors are a little too high on the blanking line.... hmmmm....

@Darkwave

Take some nice Hires pics of the unit with the shielding off each end.... than rkauer or i could advise...

[TheCorfiot]

@Zetro,

As I mentioned earlier on, I think the problem lies with the cable makeup, esp the Fast Blanking....

Good suggestion lets have a look at it

[thomas]

@darkwave:

Run Prefs/Screenmode and check that it is set to PAL:Hires or NTSC:Hires but *not* to DblPAL, DblNTSC, Multiscan or something similar.

Remove everything but PAL and NTSC from Devs:Monitors.

[darkwave]

Okay, I've attached some photos of both ends of the cable from top and bottom angles. Hopefully this will shed some light on the problem. I really have no idea what I'm doing when it comes to the insides of cables!

[Zetr0]

@Darkwave

Thank you very much for some awesome res pics!!!

looking at it there is an error in the cable, as its not made to this generic spec

http://pinouts.ru/VideoCables/AmigaScart_pinout.shtml

its using only one resistor not two, and there is no 1kohm resistor on pin 8 of the scart (audio / rgb switch) and its using pin 23 for somthing!?

if you want i can post you a couple of the needed resistors to fix this and include a visual "HOW TO FIX IT", or as you live in the UK you can post it to me, with a nice SAE and i can spend 5 minutes sorting it out for ya and post it back.

[darkwave]

Thanks for the offer Zetr0. I've sent you a PM.

[Zetr0]

indeedy, i have replied too

[ant512]

The timing problem has no impact on the video circuitry, so that can't be the cause of the problem.

[Zetr0]

@ant512

looking at the pics that darkwave posted there is an error in the cable.. infact i am surprised the A600 functions to be honest...

anyway its not gonna hurt to test it here with another A600 / A1200

[TheCorfiot]

Originally Posted by Zetr0

@ant512

looking at the pics that darkwave posted there is an error in the cable.. infact i am surprised the A600 functions to be honest...

anyway its not gonna hurt to test it here with another A600 / A1200

@Zetro,, mmmm said the cable was suspect, Fast Blanking level probably incorrect.

The AV switching on Pin 8 does not work with all TV's,, Modern ones are probably all OK, but for example, early Panasonic's (worked as design engineer for them), did not have this enabled for UK Models, was seen as a European feature

Let us know the outcome mate. All the Best

[Zetr0]

will do, and take hardware pron... worse case scenario, i shall buy some scart cables from pound land and (re-engineer them)... sheesh i could make a mint.... the components wouldonly cost £3 to buy LOL!!!!


hmmmm