I cant overclock my sega genesis! help please!

[maxxfarras]

Hi again guys,

Sorry for my English I hope that you can understand me.

Some time ago Jorge Nuno (thanks again Jorge) gave me some instructions for get overclocked my sega genesis, the problem was that I cant find a 4 pin oscillator so I tried to construct the oscillator for using a 10 Mhz crystal, a 74HCO4 I.C and a 33 pf capacitor as Jorge explained me with great detail.

So when finally I got a chance for go to the electronics store and I got the electronic components, my circuit dont worked.

The problem is that I cant get the genesis system works, the screen only still black. I dont tried to use a halt switch, (because I suposse that 10 mhz dont need the halt switch) and my sega genesis is an "non TMSS model 1 with the high definition graphics logo" with a signetics main cpu. I cutted the pin 15 trace which I think is below of the main cpu in the genesis motherboard, Its that so in this case, right?

I double checked cables, instructions and connections, I have some experience with soldering, in fact I was succesfull with the s video mod...
but my electronics knowledge is near to zero ...maybe the crystal could be have a polarity?

Any idea about which could be my mistake, maybe I dont cutted the correct trace from the 68 000 cpu...?

Thanks beforehand.
Rafael

[TmEE]

if you reverse the mod (repair the cut trace) will things work ?

and having some pictures of the mod will be helpful.

[Ace]

my sega genesis is an "non TMSS model 1 with the high definition graphics logo" with a signetics main cpu.

There's your problem. Signetics CPUs can't be overclocked. You would need to completely replace your CPU with an actual Motorola CPU in order to overclock it. You're best off just getting another Genesis Model 1 to overclock.

[maxxfarras]

if you reverse the mod (repair the cut trace) will things work ?
and having some pictures of the mod will be helpful.

Yes TmEE, it works, I soldered a small cable for repair the trace and all works normal. I will try of take some pics from my mod and motherboard of my genesis. And I will post them later. Thanks for your reply man

There's your problem. Signetics CPUs can't be overclocked. You would need to completely replace your CPU with an actual Motorola CPU in order to overclock it. You're best off just getting another Genesis Model 1 to overclock.

Really? TmEE told me time ago that could it be very possible get overclocked my sega genesis even with a signetics cpu...

[Jorge Nuno]

Maybe the circuit isn't working, or you assembled it wrong... Without pictures is difficult to tell.

You could try with another logic port, and with or without cap..


Or you could test your luck connecting the EDClk to the 68000

[TmEE]

Signetics CPUs do overclock so its not the problem, 12MHz will work very well.

[maxxfarras]

Signetics CPUs do overclock so its not the problem, 12MHz will work very well.

Great, so I will keep trying

Maybe the circuit isn't working, or you assembled it wrong... Without pictures is difficult to tell.

You could try with another logic port, and with or without cap..

I will try that possibilites this saturday, in any case I will try to put some pictures tomorrow also.

Or you could test your luck connecting the EDClk to the 68000

Do you have some link for try it this please? I dont have idea how can I do this

[Ace]

Signetics CPUs do overclock so its not the problem, 12MHz will work very well.

So then why the hell does every place I have previously seen say that Signetics CPUs can't be overclocked?

[Jorge Nuno]

Do you have some link for try it this please? I dont have idea how can I do this

Nope. I'll tell you now:

You can grab EDClk from the cartridge slot, pin15, side B, or from either terminal of the little coil marked FB7 on the board.

Connect it to the 68000 clk pin after disconnecting any other clk going there

[TmEE]

So then why the hell does every place I have previously seen say that Signetics CPUs can't be overclocked?

its just rumors basically, that came from the people doing like 16MHz+ clocks. From all the signetics MDs I've messed with, all have worked flawlessly up to 12MHz.

[ApolloBoy]

So then why the hell does every place I have previously seen say that Signetics CPUs can't be overclocked?

One word: Misinformation.

[maxxfarras]

You could try with another logic port, and with or without cap..

I did it! I get overclocked my sega genesis, I just drop the capacitor as Jorge suggest me and it worked perfectly with 10 MHZ! Thanks so much guys!

However when I tried with Strider the slowdown dont dissapear completly in the antigravity boss. However the slowdown is noticeable minor, It is normal?

-In road rash II is little noticeable but the game runs a little more fluid

-No more slowdown in sonic 1

Some other questions for TmEE:

Do you know how so much I need to overclock the signetics cpu for eliminate completly the slowdown at games or for get road rash so fluid as the xbox neogenesis emulator with overclock enabled?

Do I need a halt switch for get overclocked to 12 MHZ the signetics cpu, or it worked for you without the halt switch?

THX

[TmEE]

you only need halt switch if you plan to change clock on the fly, in other cases not... the models with Signetics CPU do not work well above 12MHz, and 12MHz is around the highest point where most games still work with no or minor problems, above that things start going downhill.
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.

[Ace]

its just rumors basically, that came from the people doing like 16MHz+ clocks. From all the signetics MDs I've messed with, all have worked flawlessly up to 12MHz.

Well that explains everything. So it's just a CPU that can't be clocked as high as Motorola's 68000 then?

It makes me wonder: how high can Hitachi's 68000 be overclocked?

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.

Seriously? *puts 32X on region-switched Genesis Model 1 and pops in Road Rash II*

[TmEE]

Well that explains everything. So it's just a CPU that can't be clocked as high as Motorola's 68000 then?

It makes me wonder: how high can Hitachi's 68000 be overclocked?

Hitachis are the best overclockers, Signetics ones worst, but the units where you see Signetics ones (VA4 and lower) do not overclock over 12...14MHz, you can replace the CPU but it will not overclock... like MD2s... the Hitachi in my MD2 will run fine up to 20MHz, just the system itself won't. most games will crap out at speeds higher than 12MHz, only one game that seems to be fully overlcocking tolerant is flashBack, that one ran with no glitches at 17MHz !!!