I cant overclock my sega genesis! help please!

[maxxfarras]

Well I will try with 12 MHz now!

You will never get Road Rash fluid, you can get it smoother but not fluid.
and for Road Rash, switch to 50Hz to get a huge inprovement, the game does not care for 50/60Hz for gameplay speed, and in 50Hz you get 50% more VDP bandwidth which is the key factor also for that game.

Well in my region we use ntsc system, so I suposse that road rash runs in 50 HZ right?, so I must go for the 12 MHz overclock.

[kool kitty89]

12 MHz oscillators seem to be more common/cheaper on ebay as well (at least recently and in small quatities).

TmEE, the model 1 VA5/6 revisions are the only models of MD/Genesis that will like more than 12 MHz overclock, with later models not liking more than 10 and earlier up to 12. (but, practically, 10-12 Mhz is the highest games like anyway)

BTW, are there many (or any) cases with 10 or 12 MHz where switching speeds after booting is necessery or preferred or is omitting the halt switch OK?

Well in my region we use ntsc system, so I suposse that road rash runs in 50 HZ right?, so I must go for the 12 MHz overclock.

No, NTSC is 60 Hz (or actually slightly less, around 59.5 Hz iirc), PAL is 50 Hz, but PAL tvs tend to work with either, not so for NTSC sets. (maybe HDTVs, but they'll tend to look worse in general for retro games)

[TmEE]

VA5/6 are indeed the best overclockers, I've heard of some 28MHz stuff happen even !!!

10MHz never requires a half switch, and 12MHz should not either.

[kool kitty89]

VA6 is also nice with the open space where the EXT port would be. (for AV mods and such -though I'm considdering using that DE-9 port for AV connections and riging up a coresponding cable)

[maxxfarras]

Hi again guys, Im in problems again, now I tried the 12 MHz overclock but dont worked. As before Im using only a 74HCO4 I.C and the 12 MHz crystal (Im not using the 4 pin oscillator because I cant find it). Maybe I need to put some capacitor, because I switched from 10 Mhz crystal to 12 Mhz crystal...Jorge can you please help me again with a suggestion for this?

Thanks again for your time and patience guys.

[Ace]

VA6 is also nice with the open space where the EXT port would be. (for AV mods and such -though I'm considdering using that DE-9 port for AV connections and riging up a coresponding cable)

Yeah. I put the S-Video jack on my modified VA6 Genesis Model 1 in that empty spot. Perfect spot for an S-Video jack.

[maxxfarras]

No, NTSC is 60 Hz (or actually slightly less, around 59.5 Hz iirc), PAL is 50 Hz, but PAL tvs tend to work with either, not so for NTSC sets. (maybe HDTVs, but they'll tend to look worse in general for retro games

So, Road Rash works better in Pal format? never thought that...Could it be because the VDP takes more time for display the screen updates, so in that way the cpu haves more time for calculations? or I misunderstood everything?


I have an LCD television and it supports pal format, the sega genesis looks great with s-video in that TV...do you recomend a pal mod in my sega genesis for better gameplay with roadrash?

Returning to my overclock problem I noticed that something very strange it happens, and took me some time to discover the reason. When the cable which go from the (10 Mhz) clock output to the 68000 is long enough the overclock dont works!

But when I use a short cable the overclock works perfectly...!

Someone could tell me please what the heck is happening?, its very confusing for me

Thanks again

[kool kitty89]

Maybe the clock signal becomes unstable when the wire is too long, maybe the wire has too high resistance.

[maxxfarras]

I give up! (for today at least)

I tried to do the cable shorter and it dont worked again, so I used again the same cable and it worked but after of some tests dont worked again, something very strange ocurrs. Maybe it is some kind of interference. I say it also because when I stayed close to the sega genesis and after that I moved then the game frezees! ( It remember me a Mr. Bean´s episodie lol!).

All that I can conclude is that my circuit is very "inestable". Someone has experienced something like this when did overclock? Could it be that my oscillator is homemade? If that is the case, maybe the solution could it be to order an oscillator from ebay...

Could someone say me if someone had this kind of problem with a "stock" (non homemade) oscillator when did overclock?

At least now I know that my sega genesis its overclockable...

[Jorge Nuno]

These kind of "homemade oscilators" are somewhat instable, as you have already noticed. You can improve the their stability, by connecting the unused gates' inputs to GND or Vcc, and adjusting your oscilator impedance with little caps (less than 33pF ones, like 22/18/15/whatever) on both the input and output. For the "cap tunning" process is advisable an osciloscope so you could see the wave of the clock signal, but still, it's possible to try out different caps and see which ones maximize stability.

Without caps, there might be a chance that your circuit may be oscillating in the 3rd overtone of your crystal, and of course 30MHz it's too much for a hardware stock MD.


Anyway if you're tired of your oscilator, you could still try the ready-to-roll EDClk signal, and see if your MD supports it. Or better, get a 4-pin oscilator with the frequency of your choice, or a divide-by-N circuit and supply the MClk signal to it.

The 4-pin, metal can oscilators are perfect though. Those things just need power, and puff! there's your nice sinewave clock signal on its output.

[maxxfarras]

Thanks again Jorge, I will try to find 4 pin oscillators of 10 and 12 Mhz. In any case I dont have an oscilloscope and I have no idea how use it. I have very few experience/knowledge with electronics devices...
do you can recomend me some site online for buy the oscillator?



Edit: Ohh and my sega genesis did not supported the EDclk, at least I think so...

[Jorge Nuno]

I usually buy electronic stuff from farnell/ebay/local shop.

http://www.farnell.com/

It seems mexico is not on the available coutries, though..

There are other big distributors like RScomponents and digikey.