Stedy's RGB to SCART cable

[alexh]

Originally Posted by ferix

I tested some other machines, like a MSX, a Sinclair Spectrum +2, and I got the same.

Could it be that the video processor in this TV does not like 288p mode? (i.e. field flag never changes?)

[Photon]

Ace. My A600 portable is on the autopsy table right now, as a matter of fact. I do have some noise (in fact, slight pixel snow) on the video to the Joytech PS2 lcd. - Despite a new perfect cable.

I can definitely try replacing caps - or is that for composite only? (My LCD does RGB, and on a CRT it looks fine*). Did you do the 3 caps near the RF modulator, or did you do all electrolytics on the board? Did you change the value of the caps to something in your opinion better, or a straight swap?

I have a car TV from China here that was horrid in composite. I might hook it up to the A1200 just for a test, it sure didn't like my A600 (superblurry superflicker in 640x256 PAL...)... was hoping to hack it for RGB... but maybe it will at least output a less crap picture with composite via your adapter.

* Since the "snow" appeared recently I'd need to check that.

[Stedy]

Originally Posted by Photon

I can definitely try replacing caps - or is that for composite only? (My LCD does RGB, and on a CRT it looks fine*). Did you do the 3 caps near the RF modulator, or did you do all electrolytics on the board? Did you change the value of the caps to something in your opinion better, or a straight swap?

I replaced every single electrolytic capacitor in my A600. Five of them had the 'fishy smell of death' when de-soldering them which indicates the electrlyte had failed. Two were in the audio circuit, the other three in the power input circuit.

The large electrolytic capacitor right next to the composite video output, is not directly related to this connector, it is bulk decoupling for the video chips. The capacitors next to the CXA1145 are those that feed the composite output.

Ian

[Photon]

The interference is on the RGB output tho. But I'll have a go at the electrolytic caps anyway.

[ferix]

Originally Posted by Stedy

You're in Tokyo a busy place, hope you enjoy the break.

Yes, I do
Too much people, too much places to see, but all is beautiful there.
Now I'm at Kyoto. And the last three days I was at Takayama.
I have no words to describe such places.
But I think that It's a wonderful country to visit, but not for living... (at least as an occidental alien).

Originally Posted by Stedy

For the MSX and the Sinclair Spectrum +2, were you also trying to use RGB mode?

Yes, I'm trying to use the RGB mode too.

Originally Posted by Stedy

I don't suppose you fancy removing the back cover from the TV and taking some photos?

I'll do that as soon as I come back from Japan...

[Photon]

Yup, occidental aliens != oriental aliens

[Stedy]

Hi,

I've just finished building one of these Macrovision killers, http://www.hobby-electronics.info/pr...ionKiller.html so that I can watch protected videos on my Sony TV, which gets upset by the protection mechanism. As it reconstruct the sync signal, I will try it with the A600. The core device is the LM1881 sync stripper, a common video IC.

I know a sure fire way of creating a 'clean' video signal from the Amiga but the two main chips cost £35.

Hope to experiment this coming weekend.

Ian

[vroom6sri]

Sorry to post a question which probably adds nothing to this thread but here I go.

Is there a working cable I can buy to connect my A1200 to my new LCD TV via the scart input or, if I am understanding what has been written correctly, are there just too many variants to get a "perfect" working one? If I could get such a cable would the picture really be much better than connecting it as I am doing at the moment via the aerial input?

[KillaByte]

@vroom6sri:
Erm ... in comparison to the aerial input? Different worlds I'd say since the aerial input most probably is even worse than Composite which already is bad enough.

@Stedy:
Nice work man - good to see that someone with the right background has a look at this. Over the years I've seen many RGB->SCART cables and only a few with the same pinout

I'm especially grateful that you shed some light on the fact with the CSYNC voltage. I was puzzled why one of my cables would have a resistor on CSYNC.

I built myself a custom cable to connect my A1200 to my Sweetspot RGB capture card. With that and DScaler I can use my Amiga on my TFT screen (or even windowed on my Windows desktop)

The card doesn't seem to bother that CSYNC is too high. But on my next cable I'll include a resistor.

I was thinking about building a SCART cable with 75 Ohms coax cables for RGB and CSYNC (just butcher an old SVGA or good SCART cable). But those cables don't have enough non-coax lines for all the other signals.

Would you mind checking the impact of using impedance matched coaxial cables for RGB + CSYNC?

[ferix]

Here are the photos I promised you.

A general view of the LCD TV controller board:



... and a closer view of the controller chip (FLI8125-LF):

[Stedy]

Hi,

Have a few response to make so in order.

@vroom6sri

I don't make or sell cables. If we can sort out the compatibility problems, more on this later, there may be an adaptor PCB that takes an appropriate lead from the Amiga and has a SCART socket. Wiring cables takes too much time to be commercially viable and is easy to make errors.

@Killabyte

Thanks for the kind words.

The sweetspot capture card looks interesting. I know the NXP SAA7118 device quite well, when you can decipher the bloody manual it can do some clever things. The BT878 device I'm aware of it's capabilities. I'm amazed the TTL CSYNC signal has not upset it but if it is working, do not screw around with it.

With regards to cabling, shielded impedance matched cables are of course the best. You should be able to hack a VGA cable. From what I remember, the HSYNC/CSYNC signals are shielded.

My prototype SCART cable only had an overall shield, which was connected only at the TV. The RGB connections were made using twisted pairs with no shielding. Each video connection was maybe 150mm and it works fine.

@Ferix

Back from your holiday already?

I'm aware of the Genesis/ST Microelectronics parts, unfortunately without an NDA can not get datasheets. Thanks for taking the TV apart though. I'm sure Zetro admired the pron.

@Thread

I did a quick experiment tonight, I hooked up my Macorvision circuit to the Amiga output to see what happens, not a lot.

Of interest were the CSYNC and ODD/EVEN outputs. The composite video output of the Amiga was fed into the LM1881 device on the board. The CSYNC output was a TTL level copy of the CVBS signal, without colourburst.

Of note was the fact the odd/even signal was stuck high, indicating that the chip could not detect odd/even fields of video, due to a lack of equalising pulses and possibly field sync pulses.

For the benefit of the thread, equalising pulses are used to discriminate between odd and even lines in a frame of video and to provide synchronisation for the top of video scanline. This is only applicable for interlaced video where in 1 field (2 fields make a frame) you draw lines 1,3,5... up to 312.5 for PAL and on the second, even field, you draw lines 2,4,6.. up to 312.5 to give 625 lines of video, with 575 full lines and 2 1/2 lines.

Back on topic, how to fix this.

The complete overkill way would be to use a video decoder, like the ADV7184 which handles RGB/SCART and then take the digital video and convert it back to analogue using a video encoder like the ADV7393. This does handle non-standard video but the two main devices cost £30.

The cheaper option, would be to take the H&V Sync signals from the Amiga and create the equalising and field sync pulses using a small, cheap CPLD, which costs around £3-5. The design would also provide the CSYNC pulses to the TV, reduced in amplitude of course.

Beside my PC is a Xilinx Coolrunner-II CPLD starter kit, which I have been waiting for a project to use it on. Think the ideal project has been found.

Unfortunately work will cease for a few weeks due to other commitments.

To those following the thread and who have built SCART leads, do they always work fine with a CRT TV?

I'll be back in 2-3 weeks.

Ian

[KillaByte]

Originally Posted by Stedy

If we can sort out the compatibility problems, more on this later, there may be an adaptor PCB that takes an appropriate lead from the Amiga and has a SCART socket.

Aah - an adapter PCB. Never thought of that before (maybe because I suck at making my own PCBs). Sometimes my own thickness amazes me

That would get rid of quite a few problems - for example one could use a good SCART cable with coax leads. That way I wouldn't even have to build a custom cable for my Sweetspot since they already offer a very high quality SCART adapter cable. You wouldn't even have to use a lead between the PCB and the Amiga - just make it plug straight into the video port. Minimize the way the signal has to travel through a potentially crappy cable.

Originally Posted by Stedy

The complete overkill way would be to use a video decoder, like the ADV7184 which handles RGB/SCART and then take the digital video and convert it back to analogue using a video encoder like the ADV7393. This does handle non-standard video but the two main devices cost £30.

Wouldn't we be halfway down the road of building a DIY SD/FF with something like this?

Originally Posted by Stedy

The cheaper option, would be to take the H&V Sync signals from the Amiga and create the equalising and field sync pulses using a small, cheap CPLD, which costs around £3-5. The design would also provide the CSYNC pulses to the TV, reduced in amplitude of course.

I guess you lost me there - wasn't the amplitude reduced CSYNC from the Amiga good enough already? Or do you just want wo make sure that we get an absolutely standards conform signal to avoid any compatibility problems?

Maybe there could be two versions - one for the cost conscious consumer with no active parts (or maybe even with the CPLD) and one deluxe "end all your amiga video worries" version featuring the video decoder. On that one a S-Video and (better?) Composite output could also be included.

You see the idea with the adapter PCB really got my thoughts going

[Stedy]

@killabyte
A PCB design is under consideration, for when I get back to the UK. Currently sitting around the pool whilst on holiday in majorca. Didn't bring my laptop so can't design circuits

The video decoder device I mentioned is part of my updated scandoubler design, utilising the Averlogic AL250 in YCrCb mode to better suit 18 bit LCD panels, if the screen refresh rates are ok.

The encoder device supports composite, Y/C (S-Video), RGB & YPrPb all via I2C conttrol. A neat solution. Plan to buy some of these from Farnell for video experiments shortly.

The CPLD is to create the equalising pulses for
the TVs benefit. This approach should also work with other retro equipment and modern TVs.

Time for some sangria!

[alexh]

Originally Posted by Stedy

utilising the Averlogic AL250

Is this suitable for use on Amiga? I thought it only had 16-bit input and AGA is 24-bit.

[Stedy]

Originally Posted by alexh

Is this suitable for use on Amiga? I thought it only had 16-bit input and AGA is 24-bit.

My plan is to use the YCrCb colourspace and thus avoid any potential gradient issues. DVD's use YCrCb co
our encoding.

99.9% of LCD panels only support 18 Bit colour (262144 colours) so the dithering algorithms they employ will smooth out some imperfections.

The big unknown with the AL250 is how it will work with a VGA panel with 50Hz video. The plan is to have a protoype this year.

Ian

[Supamax]

Hi Ian,

I have two SCART cables:
- one bought by me (when I bought my A500, MANY years ago)
- one which was given to me by a friend of mine, a few years ago

The first one worked perfectly with my CRT monitor Philips CM 8833 and with my CRT TV Telefunken PALcolor MP 150.

It doesn't work (black screen) with my recent CRT TVs Philips 14PT1574/00C and Mivar 14 P1.

AMIGA OUT                                SCART IN
---------                                --------
pin  3 (RGB red) ------------------------ pin 15 (RGB red)
     4 (RGB green) ---------------------- pin 11 (RGB green)
     5 (RGB blue) ----------------------- pin  7 (RBG blue)
    10 (composite sync) ----------------- pin 20 (composite video)
    16 (GROUND) --┬-------------------┬-- pin  9 (RGB green GROUND)
    17 (GROUND) --┤                   └-- pin 13 (RGB red GROUND)
    18 (GROUND) --┤
    19 (GROUND) --┤
(*) 20 (GROUND) ==╧====================== pin  5 (RGB blue GROUND)
    23 (+5V) ---------------------------- pin 16 (blanking)

audio plug: L+R GROUND ------------------ pin  4 (audio GROUND)
audio plug: L --------------------------- pin  6 (audio L/mono)
audio plug: R --------------------------- pin  2 (audio R)

(*) pin 20 is connected to pin 5 via the cable grounding/shielding

The second one works perfectly with two recent CRT TVs: Philips 14PT1574/00C and Mivar 14 P1.

I don't know if it works with my CRT monitor Philips CM 8833 (didn't try it yet).

AMIGA OUT                                SCART IN
---------                                --------
pin  3 (RGB red) ------------------------ pin 15 (RGB red)
     4 (RGB green) ---------------------- pin 11 (RGB green)
     5 (RGB blue) ----------------------- pin  7 (RBG blue)
    10 (composite sync) ----------------- pin 20 (composite video)
(*) 15 (clock out) ==╤=========╤======╤== pin  4 (audio GROUND)
    16 (GROUND) -----┤         |      └-- pin 18 (blanking GROUND)
    17 (GROUND) -----┤         |
    18 (GROUND) -----┘         |
    22 (+12V) ---------[R1]----|--------- pin  8 (status/switch)
    23 (+5V) ----------[R2]----|--------- pin 16 (blanking)
                               |
audio plug: L+R GROUND --------┘
audio plug: L --┬------------------------ pin  6 (audio L/mono)
audio plug: R --┘

R1 = R2 = 82 Ohm +/- 10%

(*) pin 15 is connected to pin 4 via the cable grounding/shielding

[alexh]

Originally Posted by Stedy

My plan is to use the YCrCb colourspace and thus avoid any potential gradient issues.

Which means it will have to be an internal mod?

Originally Posted by Stedy

The big unknown with the AL250 is how it will work with a VGA panel with 50Hz video. The plan is to have a protoype this year.

From a quick read of the datasheet it does not appear to perform scan rate conversion. i.e. Vertical Refresh in = Vertical Refresh out. If true, as you suspect, it won't work with most LCD's with an Amiga in 50Hz modes.

[Stedy]

Hi,
@supamax
On your first cable you have no +12V connection to pin 8 of the SCART lead, this means the TV is not set to 4:3 RGB
mode.

Ian

[Anemos]

Originally Posted by Stedy

My plan is to use the YCrCb colourspace and thus avoid any potential gradient issues. DVD's use YCrCb co
our encoding.
n

Interest thread ..
@Stedy i found this on siliconchip.com.au
http://www.siliconchip.com.au/cms/ga...?a=102648&i=12
has also full shematics and pictures of this..(press next image)
first look is easy constraction.. but i cant try that this time ..

[ferix]

Originally Posted by Stedy

Back from your holiday already?

Yes, I came back last week's tuesday, but I was too busy for post replying. You know, too much work waiting for me... :P

Originally Posted by Stedy

I'm aware of the Genesis/ST Microelectronics parts, unfortunately without an NDA can not get datasheets. Thanks for taking the TV apart though.
I'm sure Zetro admired the pron.

I know It. But I promised you such photos.
Anyway, I love pr0n too...