Jaleco Megasystem 1A 16 bit Overclocking Guide

[Hammy]

Overclocking the Megasystem 1
GUIDE

I keep getting asked so the information is now compiled here separate.

1. 6.00 MHZ STANDARD

2. 8.00 MHZ / 10.00 MHZ (STABLE)

3. 12.00 MHZ (NOT STABLE)




8 / 10 MHZ
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To overclock to 8 or 10 mhz a cpu replacement is not always needed if your original CPU can cut the mustard.
It's worth testing the faster clock before thinking about a replacement.

To perform the mod:

1)
Lift pin 4 of IC M21 IC HC04 (no longer connected)

2)
Install a 8mhz or 10mhz 4 pin OSC into the empty location @ D8
Connect the power and Ground pins (one will be missing and need jumping from the bigger pinout.
(Don't use position F1 the PWR + GND is messed up)

3)
Add wire from the osc out to MAINCPU (5C - pin 15)

4)
Good to test, use rodland or something, if it's not stable at 10mhz consider CPU replacement to P12/P16 or going for 8mhz that is within spec. of the original processor.



12.00 MHZ (NOT STABLE)
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An easy mod but never works
Maybe it will work on some boards but this has been tested on 3 setups now not stable.

1) Lift pin 4 of IC M21 HC04 (no longer connected)

2) Add wire from Pin 8 IC M21 HC04 to the now empty pin 4.

3) Good to test, use rodland or something, if it's not stable remember you are pushing luck so drop down lower.




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ADDING A SWITCH:

Not a problem, 3 position switch.
Middle pin = CPU clock pin
1st Side = Pin 4 of the HC04 (isolatedfrom the board)
2nd Side = New clock signal (OSC Output)

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GAMES WITH SLOWDOWN:

Rodland - Slowdown improvement with any overclock, still seems to drop @ 10mhz+ (code issue i guess...)
EDF - Slowdown improvement with overclock best @ 10mhz+
Big Striker - REQUIRES 10mhz OR BETTER or Unstable!
Phantasm - Slowdown improvement with overclock best @ 8mhz+
P47 - Slowdown improvement with any overclock, still seems to drop @ 10mhz+ (code issue i guess...)
ST dragon - This had some slowdown @6mhz but not tested on an overclocked setup yet.

Others?

 

[Hammy]

NEW HACK 7MHZ - no added clock, used 7mhz from onboard!

1) Lift pin 4 of IC M21 74HC04 (no longer connected)

2) Add wire from Pin 6 IC H3 74HC04 - MAINCPU 5C - pin 15

 

[opt2not]

Just wanted to follow-up with my experiences with these mods.

At first I tried the easy 7mhz hack, it went fine but I wasn’t getting the performance I was looking for in games like EDF or Rodland. So I decided to do the cpu upgrade + 10mhz mod.

It’s not a greatly difficult mod. The hardest part is removing the old cpu.
But with a bunch of flux, some new solder and my trusty hakko FR-300, I was able to get it off really cleanly.

Installed a socket for the cpu and fitted the 16 variant :

I had a left over 10mhz Crystal from upgrading my cps1 mobo, so I fitted it onto the spot indicated in Hammy’s earlier post.

Jumper wire from the osc to the new 16 CPU (make sure you connect to pin 15! I made that mistake the first time around)

Then of course lifting the pin 4 on IC M21, to finish the hack off.

The results!

Big Striker runs stable!

All the other games run as they should and have less slowdown from what I can tell. I’m going to do more testing but so far this was a success.

 

[Hammy]

Just to clear this up, the overclock is not mandatory... Although it is nice to have and unlocks some doors...
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List of games that are perfect / true to original on stock system (without mods):

P47
Avenging spirit
Plus alpha
Kick off
St, Dragon
Rod land
Soldam
Astyanax
Ninja Kazan
Hachoo
Bases loaded 2 jap
In your face
Samurai shingen
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Games that are ported from other hardware / experimental:

Legend of makai (runs well on most standard motherboards... working on better compatibility....)
EDF (runs well as standard with minor slowdown, 8mhz+ recommended)
Big striker (10mhz required)
Peek a Boo (coming soon , 100% port runs ok on stock speed system)
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Future / WIP (not released / not finished):

Cybattler (10mhz and extra sprites HW)
Chimera beast (10mhz and extra sprites HW)
64 Street (10mhz and extra sprites HW)
Mustang (8mhz and extra sprites HW)
++??

 

[dos]

List of games that are perfect / true to original on stock system (without mods):

By stock system you mean 6mhz? I was under the impression some of these games in the list came with a faster CPU. Or was the faster CPU always underclocked? My P-47 came with 6mhz so I can't check

 

[Hammy]

By stock system you mean 6mhz?

Exactly, the 1a / romboard system always comes with this clock speed regardless of CPU chip model.
Any games with slowdown on the top list are exactly as released.

Bumping the speed can fix slowdown to some extent on these games if they have any (they are all capped so won't run too fast).

I was under the impression some of these games in the list came with a faster CPU.

Only non- romboard hardware used faster CPU but we can run the games with the upgrade(s).

 

[opt2not]

Oh man, Cybattler would be awesome to run on this multi! I’m so down for that extra hardware board.

 

[Hammy]

Oh man, Cybattler would be awesome to run on this multi! I’m so down for that extra hardware board.

It's on hold at the moment , way too much going on!
When everyone is setup with the multi and there's more with overclock i'll get back to finishing it hopefully...