Megadrive 2 composite B&W picture

[dadou]

hi,   i did some mod on my Megadrive 2 pal version this one:

50/60hz switch
Jap/Eng switch
RCA Mod
Composite Mod
Led Mod
Improving sound and video on scart cable

some pictures:





the problem i have is that i got B&W picture on my Pal TV in composite i do also this circuit to solve it : http://www.zipplet.co.uk/index.php/cont ... cs_mdpal60
but it's not working
i have the MB3514 chip inside and not the CXA1145 but i see it's the same one

how can i do to solve this problem?

thx in advance

[albino_vulpix]

Welcome to the boards!

Two thing I can think of for why this isn't working. First, the link you provided states that this will not work with an MD2. Not sure what video IC he tried it on though; could be that the IC you have works. If this is the case, then your circuit needs to be "fine tuned". Wire lengths affect the clock just enough to throw your TV off.

[dadou]

hi, for the site i didn't see the note on it  

i did also this circuit : cristal oscillator of 4.43 instead 28 MHz

i did this one because my chip MB3514 don't have an oscillator driver

i did like it's specified in the datasheet:

pin 5 to ground with a series capacitor, 100pF

connect a 0.1uF capacitor to pin 6, and connect the other side of this capacitor to the oscillator output.

pin 7 to ground

but one more time i got a B&W picture  

[jpx72]

for MD1 i have this schematics, but for MD2 , sorry

[l_oliveira]

Have you tried to lift the pin7 (NT/PAL) of the video encoder and tie it to GND ?

Considering that your console is already PAL, why would you need to add another clock source ?

Don't you want to get PAL60 ? you can tie the NT/PAL pin on the video encoder to get it locked into PAL mode. If I am not mistaken, that pin changes state when the VDP is set to NTSC.


Edit: After consulting with Tmee, I got informed that the clock divider on the MD changes from 12 to 15 when switched to NTSC. So please disregard what I said here ...

[dadou]

You can see here all the things i tried  http://sega-16.com/forum/showthread.php?t=10522 for now i didn't find any solution 

[dadou]

finally i got it to work!! with the help of hacksquad, Tmee and Jorge Nuno of the sega-16 forum here's the schematic:



now i need to explain some things:

in the schematic you can see this: "cut the orignal trace" you need to cut the trace like this picture where you see "disconnect":

http://www.fileden.com/files/2008/4/21/1876835//MD2fujitsuClock.jpg

in the schematic you have a wire from "after R61" in the same picture you need to solder a wire after the trace you cut

and finally solder the signal after the capacitor of 100nf in the point where you see "feed clock here"

this is the result:

Pal Mode:



NTSC  Mode:

[albino_vulpix]

Question: I see the NAND gates are of the LS family and the inverters are HC. Is this important?

[dadou]

for the circuit with the oscillator only the HC family are working, for the Nand gate i use LS because i only have this one but HC will bo good too i think