Dissecting the Portable Megadrive, Fun fun.

[Qjimbo]

Well I just went and bought it one of these from my local Argos. Really nice actually, though the PSG is too low by 7 semitones, and the scaling is a bit weird, but I still think it's pretty damn cool.

Anyway, I had to take this apart to figure out whether it was possible to say, put custom roms on, so here's my guide to taking it apart...


Step 0: Admire the beauty.


Step 1: Remove the batteries and every screw on the back. 5 screws in total, the battery panel screw and a screw on each corner.


Step 2: Prize open the the case. I found that around the volume control is a good place.


Step 3: Work your way around the edges. There are 2 clips on each side.


Step 4: Once you have undone all the clips, pull apart the case. The area around the battery compatment is stuck with sticky pads, but it is fairly easy to still pull it apart.


Step 5: Remove the 2 small screws each side of the main circuit board. There are actually 4 screw holes so some people may have 4 screws to remove.


Step 6: This part is fiddly, but carefully pull the circuit board out of the case. Again, around the volume control seems a good place.


Step 7: You're done!

Now I did have problems scanning it in due to sticking out parts, so I took some pictures instead:



I believe the chip under the black plastic on the left is the CPU, and the chip on the right is the ROM.

The model numbers on the chip on the right is
M6MLT 157N1P / M6MLT I57NIP (depends if it's an I or 1)
^ Wrong, thanks IJTF_Cinder!

M6MLT157NIP
JPN EWG-D
518208

Also, when I plug this into a TV, it runs in a weird 50Hz mode with horrible scaling artifacts =/ I'm wondering if there might be some way to region mod this thing, I want 60hz!

[ken_cinder]

Part number on that chip is actually M6MLT157NIP made by RENESAS (According to a supplier listing), looks BGA placed on a secondary PCB soldered to the main PCB (Hard to tell, your pictures are a lil blurry).

I would imagine you are right about it being ROM. And if it is indeed on a secondary pcb, it's probably so they can easily put different little PCBs in these units, with different games.

Given how hard it is to dig up info on these chips (I found a few suppliers, but you'll need to order THOUSANDS at a time) you may not have the easiest time changing this thing out.

Looks neat, and if possible to change out that ROM with something more easily obtained, easily modified to play whatever games you want.

[viletim]

Pinouts for the rom in other ATGames widgets looks like this.

Code Select Expand

.     +--U--+
. A22-|1  44|-A21
. A19-|2  43|-A20
. A18-|3  42|-A9
.  A8-|4  41|-A10
.  A7-|5  40|-A11
.  A6-|6  39|-A12
.  A5-|7  38|-A13
.  A4-|8  37|-A14
.  A3-|9  36|-A15
.  A2-|10 35|-A16
.  A1-|11 34|-A17
. !CE-|12 33|-
. GND-|13 32|-GND
. !OE-|14 31|-A0
.  D0-|15 30|-D7
.    -|16 29|-
.  D1-|17 28|-D6
.    -|18 27|-
.  D2-|19 26|-D5
.    -|20 25|-
.  D3-|21 24|-D4
.    -|22 23|-VCC
.     +-----+

This one, being 16 bit, would have an extra 8 data lines (D8-D15). Region, speed, video type, scaling adjustments, and everything else is most likely stored in the ROM.

[Tiido Priimägi]

This is pretty interesting. Is it emulated or it uses hardware way ? The official MD clone on PlayAsia is emulated using some ARM...

[Qjimbo]

Thanks for the information guys!

Unfortunatly an order I tried to cancel from play asia for one of these got shipped out this morning... so I'll have to take my white one back to argos and wait for the other one to arrive! At least it'll be 60hz on a TV though. I just wish I could have got some PCB scans to compare the difference for modding, oh well. (edit: screw it, I might just keep this UK one too!)

As for these M6MLT157NIP ROMs, it seems RENESAS do have Headquarters in the UK, so I might give them a ring tomorrow and see if I can get ahold of a datasheet. If it requires those extra datalines though that seems like it might be hard to replace with another rom that does the same thing, but I know very little about electronics...

[Tiido Priimägi]

The ROM should be standard 16-bit ROM... all my pirate MD carts have ROMs with standard pinouts...

[Qjimbo]

So you're saying the pinout of that chip corresponds to the Genesis cart pinout here: http://www.gamesx.com/cartouts/gennycart.htm ?

[ken_cinder]

So you're saying the pinout of that chip corresponds to the Genesis cart pinout here: http://www.gamesx.com/cartouts/gennycart.htm ?

Pretty sure that's the cart pinout, as in the edge connector, not the ROM itself, which most certainly will differ to a point between different chips used.

[Qjimbo]

So if I removed the original ROM chip, then soldered a wire from each point on the PCB to an edge connector following viletim's pinout, it would boot from a cart instead? I'm assuming the ROM already in the device is somewhat similar to a tototek cart then?

Also Renesas' UK line sucked, the operator wanted to transfer me to a distributor and I had no idea which one to pick. So I decided to send them an email instead. Now we play the waiting game...

[viletim]

So if I removed the original ROM chip, then soldered a wire from each point on the PCB to an edge connector following viletim's pinout, it would boot from a cart instead? I'm assuming the ROM already in the device is somewhat similar to a tototek cart then?

Maybe, though a megadrive cart runs on 5v and this rom/flash/whatever is almost certainly 3.3v. I'd bet that the device needs to be setup first too (just like the Atgames handheld Sega Master System things), and guess where the setup data is located...

Also Renesas' UK line sucked, the operator wanted to transfer me to a distributor and I had no idea which one to pick. So I decided to send them an email instead. Now we play the waiting game...

What are you expecting to find in the datasheet? The only interesting thing about it is the data contained whithin the ROM.

TmEE,
How do you know there's a software emulator in there?

[Qjimbo]

In regards to the Setup data, it might not all be doom and gloom! I actually have a Double Pro Fighter Rom dumper (similar to a Super Magic Drive), and a Sonic 2 Pirate cart I could dismantle. I might be able to solder in the ROM chip from the portable megadrive into this cart and dump the ROM.

I've worked out the total size of all the roms on there is about 14MB, so it must be a 128Mbit ROM, meaning it probably uses bank switching, which means I might only be able to dump 4MB of it.

In regards to the datasheet, I just thought it might be useful to have, to see if it might be reprogrammable for example?

[viletim]

Qjimbo,

The best way to dump this ROM is with a versatile ROM reader/programer, rather than some dedicated ROM dumper. Bankswitching is a function of other chip...

Here's how I've done this in the past:
http://members.optusnet.com.au/eviltim/sega20in1/extra/romdump.jpg

Remember: If you connect a 3.3v chip to a 5v Vcc you'll destroy it.

[Tiido Priimägi]

TmEE,
How do you know there's a software emulator in there?

http://www.assemblergames.com/forums/showpost.php?p=293453&postcount=15

[phreak97]

these units are for sale here (but black and red).. theyre licensed products apparently. in some other pirate/ aftermarket licensed units (atari tv games for example) theres been just sets of jumpers for region.. perhaps theres a pin somewhere? when you get the ntsc version, take the two apart next to each other and compare everything.. there might be something connected differently somewhere? or is it pretty certain it's going to be information within the rom?

on another note.. what does the lcd run off? the thing outputs analogue video, so would it be reasonable to assume the lcd could be used to display an analogue video input?

[viletim]

these units are for sale here (but black and red)..

Really, in real bricks and mortar shops? I'll have a look for one when father's day is well and truly over.

theyre licensed products apparently. in some other pirate/ aftermarket licensed units (atari tv games for example) theres been just sets of jumpers for region.. perhaps theres a pin somewhere? when you get the ntsc version, take the two apart next to each other and compare everything.. there might be something connected differently somewhere? or is it pretty certain it's going to be information within the rom?

I have no doubt it'll all be in the rom.

on another note.. what does the lcd run off? the thing outputs analogue video, so would it be reasonable to assume the lcd could be used to display an analogue video input?

It's just a normal LCD, same as what you'd find in a camera or a phone. No analog video, each pixel is clocked in digitally.

[phreak97]

theyre for sale at gametraders marion, mark, the owner, has taken to importing alot of items, this is probably one of them, i can find out where he got them if you want.

[viletim]

theyre for sale at gametraders marion, mark, the owner, has taken to importing alot of items, this is probably one of them, i can find out where he got them if you want.

Ah, just a sole importer then. Not to worry, I'll probably buy one eventually. But I really don't have enough free time or even motivation to properly analyse the rom contents... It's not a particularly interesting job.