Sonic 2 is running THROUGH Sonic & Knuckles. That is how the "lock-on technology" works. It's using Sonic 2's data, but the Genesis sees Sonic & Knuckles. It doesn't rewrite Sonic 2's data. A lot of people would be quite angry if it screwed up doing it at some point.

I can't believe a ROM revision would cause it not to work... sounds weird to me.

As SgtBowhack said S&K does alter the code of Sonic 2 and 3 slightly so that's supposed to happen.

Your findings with Sonic 2 UK/JAP cats are interesting though, this could be a memory timing issue as suggested previously by DevSter so I've posted a message on his forum as he seems to be the "man in the know" about these things. If the read cycle/speed of the ROM's is different it could be the cause of the problem, although a "real" Mega-Drive can cope with the difference that doesn't mean that the Radica can. Also it would be interesting to find out if the new Volume 2 edition of the Radica (which has Sonic 2 on-board) has an updated/revised main board? (or the upcoming Street Fighter and Codemasters versions)

I really think that timing issue is bunk, myself. There's still the region issue here. I think maybe, as suggested, the Japanese version checks the region and crashes (maybe the new revision of the ROM is the same worldwide). Some copies of Sonic 2 check to see what region it is to tell the game whether or not to call Tails Tails or Miles. I'm not saying for sure it's the problem, but I'm saying it does seem more likely than timing to me. Someone should trace the address when the game crashes and see what the ROM is doing at that point.

@SgtBowhack - you are correct in thinking that timing wouldn't be an issue with the Radica!

I've tested the 'compatible' Sonic 2 cart on a REAL Genny in UK/PAL mode and on the Radica...

...if the timing were different, then the Demo's would "screw-up" on the Radica. This is not the case though, they match frame-for-frame on the REAL MD and the Radica!

@Red5 - Yeah, the JAP Sonic 2 ROM looked newer. So maybe @SgtBowhack is correct when he says that SEGA added a basic region check to later revision ROM's.

Also, let me clarify...

I should have said 'erases' instead of 'alters' when referring to what SnK does to Sonic 2 carts after they have been used in conjunction with SnK.

(hence why I said EROM and not EPROM)

It would basically 'delete' the part of the code in the Sonic 2 ROM that said : -

---add sparkles to Super Sonic by default---

(since Super Sonic in S3nK [Sonic 3 & Knuckles] also has no sparkles!)

Anyhow - I know it does 'alter' Sonic 2 somehow, as when I originally owned the games (way back when) I remember my...

"What the heck!"

...reaction to seeing no sparkes in the Sonic 2 cart AFTER having detached it from SnK!

Devster replied to my post on his forums weith a few interesting comments. He agrees that it no longer looks like a memory timing isssue BTW.Er, I think he means are you pulling power from where the ROM chip is on the Radica (which is 3.7v I think) or are you pulling it from else where (@5v?) before it gets pulled down to 3.7v. i.e. does the cart have enough power?Very interesting, so paulpsomiadis how long are your wires from the Radica board to the edge connector? And were/are they longer on the JAP unit you modded? If it's more than 3" long it may pay you to snip the wires a bit shorter and redo it (again!)

DevSter also made a couple of other techie points that I couldn't really follow so follow this link for the rest: http://devster.proboards22.com/index.cg ... 1103504018

His other points were this.
Dump the cart. data from each of the Sonic 2 carts and compare them with eachother, they might be a bit different.
Don't leave certain pins N/C. Depending the what they are they should be tied to either ground or Vcc (I'd say tie them to either Vcc or ground through a 10k resistor just for safety)

You know, that's a good point. While the rest of the Radica runs on 3.3v, that ROM may need 5. You may want to use something to pull the voltage up on the cartridge somehow, or pull it down on everything else from 5...

@Red5 - yah, I get what Devster was saying in his forum about using a higher VCC point instead of the one from thr Radica 'spot'.
So, yes - I'm currently using the 3.30v VCC from thr ROM spot.
Also checking to see if any pins on the Radica are remaining in a high (+ve) or low (-ve) voltage state for too long (i.e. 'stuck').

But bear in mind folks that this is only ONE cart, and I'm not really bothered since my U.K. version of Sonic 2 works with the Radica anyway!

Also the wires are approx. 3" - or near enough! (they can't be shorter anyhow, or they won't reach the top of the new case!)

@Gannon - I think I get what you are saying by 'reading into' Devsters post on his forum...

...basically try to 'mimick' the missing pins on the Radica by creating similar voltages for them (somehow?)

Anyway folks - more interesting news!

I got a DEAD cart (Quackshot) today and decided to use the 'innards' to wire up the Radica ROM into a cart.

For those who want to try - the N/C point on Ben's diagram is actually VCC. (if yer' reading this, please update your diagram Ben!)
It is REQUIRED for the Radica ROM to power up (otherwise it's 'black screen a go-go'!)

Okay, so I thought "Great! now I can use it on a REAL MegaDrive!"

But not so...

...WHY? Well, I tried ALL region combinations (NTSC/PAL/ENG/JAP) and just got the "Produced by or under licence from SEGA enterprised Ltd." message, followed by a black screen!

Yet the ROM still works PERFECTLY on the Radica!

Hence why I listed it with a region of: - PAL/?

The only two possibles remaining are...

1. The Radica has no region (like @SgtBowhack has said all along!)

2. The Radica is based on an ASIAN MegaDrive (PAL/ASIA)

I'll test my 'theory' when my ASIAN MegaDrive arrives in the post...

That's all for now folks!

There are Brazilian Megadrives that have a different region setting too. I'm not too sure what the differences are, but Mega Keys have settings for them. It'd make sense that TecToy would have a design for a GOAC since they're building tons of the things.
Anyway, it could be a myriad of things.
paul: too bad your copy of Quackshot is dead. I have the Japanese cart, actually

True, true! (anyone for a Budweiser - LOL!)

It could also be a Brazilian MD...there are actually many regions!

USA / JAPAN / EUROPE / ASIA / BRAZIL / FRANCE / HONG KONG

And yes, it did kind of suck that my Quackshot was a dead cart...

...but on the bright side I can play the Radica ROM again!

==VCC Voltage comparison==

REAL MD = 4.96v

Radica = 3.30v

The best way to remedy the problem is to take a reference line from a solder pad near the power inlet of the Radica (this pad measures 5.30v approx.) then add a 'pull-down' resistor to bring the voltage to approx 4.96v...

I'll update again later after some more checking...

Ookay - after a LOT of messing with resistors, I found that a 1meg ohm resistor on the 5.3v line will give approx 4.8v.

This 'would' be perfect as a voltage to run carts from - except for one problem...

...when the machine is powered off, the voltage rises to ABOVE 5v, even WITH the resistor!

This would mean that any cart plugged in would get toasted!!!

The only viable solution would be to 'feed' the 4.8v through a relay (powered by the old VCC of 3.30v) to the cart slot.

Therefore when the old VCC from the Radica ROM spot is powered to 3.3v - the Relay would switch on and allow the 4.8v to power up the inserted cart.

Thus the voltage returns to zero at power off, and we still have the required 4.8v supplied in a SAFE manner...

In other words - it's a right Royal mess-on, and I can't be bothered!

Compatibility is good enough, so lets leave it at that!

True, just as a thought though have you tried dumping the rom using your Tototek reader/writer and seeing what emulators make of it (Gens, Kega etc.) ? Or even looking through the rom dump with a hex reader to see if there's any region info in that. That would answer a lot of questions although you may have to give the rom dump to someone who knows how to do reverse disassembly to find the info.

The Tototek reader/writer will ONLY read/write to the 'special' flash card it comes with!

If you want to backup carts you'll need a backup device!

(I wouldn't be speculating if I could have already dumped the cart!)

Time will tell - if I can either get my hands on an old backup cart, or build a backup device in the near future, then I'll let you all know!

I was going to suggest trying UCon64 ( http://ucon64.sourceforge.net/ )with your Toto-Tek, if you haven't already that is, but it looks like that might only read/write to the Flash cart as well might be worth a look though.

Alternatively there's the Sega-CD transfer cable ( http://www.pages.drexel.edu/~mrp29/transfer.html ), this is a DIY/home-made cable which also allows you to dump Genesis carts. However you need a Mega-CD to get that working and I don't know if you have one of those... I might try building one of these cables later and give it a try with my system if I get bored

If you want, I can find you another one. They aren't too expensive (I got mine for less than 200 yen).

I think a pull-up circuit is still the best option I think I might use one if I ever made a portable of something lowish power, simply because I could get away then with 1 or 2 AA rechargeables and still power all of the circuits (for a limited time). But I wouldn't have to worry about uneven charging and it'd make sure that battery was completely discharged before a new charge.

@Red5 - Hmm...maybe UCON might work, dunno? I could try it I guess...

Oh and I know about the MegaCD cable (saw it somewhere else in the forum).

I own an ASIAN (RARE) MegaCD - but I'm still waiting for my ASIAN Megadrive to arrive in the post!

Might give it a try when I get everything working!

@SgtBowhack - Thanks for the offer on Quackshot, but I'm going to have to stop on this 'list' soon-ish (been spending too much on carts!)

As for the pull-up circuit. It's a good idea in theory, but they create a heck of a drain on the circuit around them! Might work, might not...