Running Megadrive on 5V, possible?

[Jega]

Cheers everyone. As the topic says, is it possible to run Megadrive model 1 on 5V or is there anything inside that really needs those 10V the adapter outputs?


(there should be a pic here)

If it's possible would it be as simple as to connect the 5V to the output-pin on these two 7805 regulators?

[blackevilweredragon]

it uses a 10v input to power BOTH those regulators (it has two because the chips in their like the NMOS 68K are very power hungry)..

So yes, you can run it on 5v, but i really would recommend leaving the regulators there (which you need about 8-9v to power both those)..

[viletim!]

Jega,
I don't see why not. Make sure you remove both voltage regulators (they don't like their Vout higher than their Vin) and link the two 5v rails together.

[kendrick]

My instinct is that if there are two 7805 regulators in there, then there's a pretty good reason that both circuits are isolated from a power perspective. On the other hand, Sega's circuit design is notoriously bureucratic, in that different comittees design different parts of the circuit board and don't bother to consolidate redundant functions like power (see the Saturn and the CDX for good examples.)

If that were a 7905 providing negative voltage on top of the 7805, then I would say that the 10 volts might be a deliberate design choice. Probably the 10 volt input is not necessary, but safer. Only Sega's engineers know for sure.

-KKC

[MNK]

Sorry for the confusion but Jega is now MNK. I couldn't register before because I tried to use a hotmail account, I think..

Anyway, thanks for the replies. I'm gonna remove the regulators but not join the 5V rails at first.

[MNK]

Too bad I didn't find the schematics earlier.. it seems 9V is needed on the cartridge pins A28 and B28 . I'm gonna try anyway since I've already removed the regulators but I doubt it'll work.

[viletim!]

MNK,
Game cartridges don't require the unregulated voltage, they are just a rom on a card after all. The +5V rail is split so the two regulators will have a roughly equal load. If you only connect one you'll only power half of the Mega Drive.

[MNK]

Yes I'm gonna connect both but not by joining the rail, that's what I meant. I'll post if it worked or not later today.

[Guest]

I imagine you will need to supply extra current if you reduce the voltage. Only one way to find out, really.

As for the cart slot having 2 connections to 9v .. either that's an error on the schematic (IIRC these are from a reverse-engineering, not Sega) .. or it's just weird and unnecessary. The system is all 5v logic, everything should trigger fine on >4v, I'd think.

[Epicenter]

.. I've got to start remembering to log in.

[MNK]

I barely have any games to try but Alien 3, Castlevania and SOTB works fine. It's been running for about 2 hours now without any problems. The headphone-socket works too. I simply bridged the input-output spots where the 7805s was originally located and then connected +5V and GROUND to the original power input.

Thanks for all the help.

[RobIvy64]

Pretty cool stuff. That should help get rid of some of the heat (not that it's a problem).

I may try this and use my Neo Geo's 5V power supply.\ since they share the same connector.

[Epicenter]

I used to use my MD in the same fashion; connected to my PC's power supply via a Molex. Bear in mind that rail offers over 40 amps! If the PSU does not supply as much current as is needed to drive all the hardware, you'll encounter problems .. or maybe damage the power supply. Granted any PSU meant for a PC should be able to more than handle what the MD can draw from it.

A side benefit that occurs to me; supplying more current may help stability with the 68000 overclocked.