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Old 30 January 2006, 12:07   #1
ST Dragon
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Defective? (RGB)-Scart SEGA Mega Drive Model 1 cable & 4:3 to 16:9 display problem...

Also, I just got a non-SEGA RGB(Scart)(Non-official) cable for my two Euro PAL SEGA Mega Drives Model I (Bulky models)
I have a standard 4:3 display 21” Flat SONY 50/60HZ EURO PAL/NTSC TV with RCA-IN, RGB-IN(Scart) & RF-In (Antenna)

All my other consoles that are connected to this TV via the RGB-IN, work perfectly, at 4:3 display ratio. But when I connected both my Mega Drives (Model I) with this new cable, the display will switch from 4:3 to 16:9 after a few minutes in random.
My TV has a button that I can switch back to 4:3, but after a few minutes it will switch back to 16:9 again.

My TV doesn’t have a problem as all my other consoles (PS-1, PS-2, DC, Saturn, work perfectly at 4:3 via RGB(Scart) constantly and I don’t thing the problem is caused by my two MDs.

This specific RGB(Scart) cable only uses these pins: 2, 6, 7, 8, 11, 15, 16, 18, 20 (pin 2 is connected to pin 6, internally)
I’ve never had an official SEGA Mega Drive Model 1 cable so I wouldn’t know if these are the right connections, but what else could be causing the random switching from 4:3 to 16:9?

Thanks in advance.

Last edited by ST Dragon; 02 February 2006 at 09:40.
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Old 30 January 2006, 23:51   #2

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Ive got a Bush 22" tv that has same issues with my ps2 two. The problem lies with pin 7 (AV Switch signal). The tv is using whatever voltage is on this pin to detemin if the screen should be 4:3 or 16:9. The system needs to provide at least 9.5v-12v to stay up in 4:3 mode, else anything between 2 and 9.5 is 16:9. 0-2v and it wont switch.

The kicker for me is that the tv isnt even a wide screen yet follows the above rules. The output of the switch signal appears to me 9v so my tv doesnt hold 4:3 image very long if at all :/. Also my tv seems to require the blanking signal else the screen stays blank on rgb. The ps2 rgb cable connect pins 7 and 16 together (blanking) with a resister bringing the blanking voltage to the required 3v. (Cable actually didnt have resister, just connected two pins - blank screen on my tv).

My Current solution is to use a scart switcher box and switch the dvd player on at same time (Interestingly needs the resistor too else blank). this puts enough voltage on the switch signal to keep it 4:3.

My Amiga has no issues with rgb , its cable provides 12v on switch signal and already had resisters on Blanking and composite signal (Both are needed to work on my tv). I think Bush must be super strict on the scart standard or something because it requires abit of work getting things working on it.
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Old 31 January 2006, 08:50   #3
ST Dragon
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That was a very imformative reply!

I connected it to another simpler TV SONY 21" 50/60HZ Mono-Sound and it worked perfectly without switching from 4:3 to 16:9 randomly, so it's obviously the TV.

I don't have a DVD player in between to turn on and increase the voltage, but I can get a Scart switcher box to increase the voltage.

I'll also check the exact voltage output of pin 7 on the Mega Drive Scart cable and try to figure a way to increase the voltage by connecting it to a 10-12V line on the Mega Drive PCB.

I'm wondering if I go ahead and install the 50/60HZ & country mod switches on my Mega Drive Model 1, will it fix this problem as well as the JPN Altered Beast cart not loading on my consoles.

I’ll do it my self this weekend.
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