MD 50/60Hz Switch Problem

[Confused]

Hi guys, I�ve just performed the 50/60hz switch mod on my PAL MD1 & I was wondering if anyone knew how to get a colour picture when in 60hz mode while using an AV cable??? I don�t understand why its in black & white considering my TV definitely supports NTSC. Is it possible without having an RBG cable?  

Tom  

[NFG]

It's quite possible that your TV is expecting NTSC colour when you feed it a 60Hz signal.  Without changing the crystal for the video encoder chip inside the MD you're only going to get 60Hz PAL.

[Confused]

Is It possible to change this crystal Lawrence?  

[Aidan]

Dumb question here:

Is your TV natively NTSC or PAL? From reading between the lines, it sounds like your TV is natively NTSC?

The 50/60Hz switch does not change the encoding between PAL and NTSC. All it does is change the output rate.  

[phreak97]

No megadrive will output colour via composite when switched from its native refresh rate! not a one! you HAVE to add a new crystal.
the problem is that when you switch it the glue chip is getting the wrong frequency (the main crystal is different from an ntsc machine to a pal one) and basically completely ignores the fact that its meant to be outputting a signal.
you have to build a small circuit onto the video encoder with a new crystal to keep colour.

[Confused]

Aidan: My TV is natively PAL but it gives me these choices:
- PAL
- NTSC 4.43
- NTSC 3.58
- AUTO

phreak97: Do you have schematics for this small circuit you mention?

[phreak97]

for NTSC colour output, the correct values are a 3.579545MHz crystal, 50pF (I used a 60pF) variable capacitor (trimmer), 15k resistor, and a 30pF capacitor. For PAL colour output, a 4.433619MHz crystal should be used instead; other values are the same.

the chip you are working on is the video encoder, it's labled CXA-1145 or CXA-1145P or something like that.

cut the trace to pin 6 before you begin, and make sure there's no trace leading to pin 5 (there shouldn't be).

Now, using good RF construction practices (keep cables as short and direct as possible, and solder as much to the board as you can), solder one end of the 30pf cap to pin 5. Solder the other end to the crystal. Solder the other end of the crystal to pin 6. Then solder the resistor from ground (pin 1, test pin 7, it might be ground and it's closer) to pin 5. Then the variable capacitor or fixed capacitor substitute from ground (pin 1) to pin 6.

turn the system on, you should get colour no matter what now. the picture may not be perfectly clear, adjust the variable capacitor (carefully) untill you get a clear picture.

[Confused]

Thank you phreak97

I guess I'm going to lose colour in 50hz mode? Couple of my games such as Streets Of Rage 2 constantly rolls after flicking it to 60hz mode, so I was hoping to have colour in both 50/60 modes. (Am I getting greedy?)

If I were to setup a switch between the 3.579545MHz & 4.433619MHz crystals, would that work well or do you think it would cause poor picture/colour quality?


Thanks again!

[phreak97]

just install the setup for the format you want, the games dont care what colour format, only what refresh rate.
if you install the ntsc crystal, itll always output colour ntsc, no matter if you have it switched to 50hz or 60hz. same goes for pal. once you have done this mod, you will freely be able to change between 50 and 60hz (providing you have installed the 50/60 mod aswel) without losing colour.

your tv shouldnt roll at all, no matter what colour format (or lack of) it's outputting. you should at least get a clear black and white image with an unmodded console.


in short: if you combine this mod, with the 50/60 mod, the consoles 50/60 will work like that of a snes, it wont change video format, just the refresh rate, and will keep colour

ps. the switch probably would lose you quality as its gonna add crap to the clock signal from the crystal.

[Confused]

Excellent!!!    

All the games that I tested running in 60 mode did display a clear black & white image as you said it would on an un-modded console.... * BUT * streets of rage continually rolls the screen slowly? Also the music is extremely slow?

If I boot the game in 60 mode it doesn�t roll but I get the:
"THIS GAME IS ONLY FOR USE IN bla bla bla" screen.

Any way thanks again, I really appreciate your help. I'll be doing this mod on the weekend but I�ll probably use a 4.433619MHz crystal which if I understand you correctly will result in PAL50/PAL60 modes.

I was also wondering about what you mentioned in an earlier post about the whole problem exists because �when you switch it the glue chip is getting the wrong frequency (the main crystal is different from an ntsc machine to a pal one) and basically completely ignores the fact that it�s meant to be outputting a signal�

I was wondering what the main crystal runs at on an ntsc machine?
The main crystal runs at 53.2034 MHz on my PAL MD. Are you sure it�s different on an ntsc machine phreak97 ?

Correct me if im wrong but wouldn�t that mean ntsc machines run at different speeds  to pal ones? (the 68000, Z80, VDP etc)

[phreak97]

yeah, they run at a different speed, but its only about 0.9% different apparently.
the ntsc crystal is 53.6931MHz, and as you see, the pal crystal is 53.2034MHz