Yet another Genesis/Megadrive mod - Video Selection board and Switchless Mod

Hi there,

I'm trying to make some mods on my Megadrive Model 1 VA3.
I have only few experiments with eletronics, so I hope I won't say too much stupid things.

I'll try to do a switchless mod (and prepare for also controlling the 32x and the MegaCD) by following the tutorials of Mmmonkey (Here, here and here).
But I'll also make another board which is a sort of Video Selection. This is an adaptation of the PAL60 mod from Mmmonkey/Zipplet, but this will work for any region and will do a bit more.

The board will have 3 positions:
- Off : the board won't do anything. If you have interference with RGB, this will let the CXA working normaly,
- Patch : the board will patch the signal if it differs from the selected region. i.e: if your console is a NTSC one, the board will only works when you switch to PAL. On US/Jap the board won't do anything.
- Override: the board will always override the signal from the main Crystal. This will also allows to make a NTSC console works on PAL TV, and a PAL console on a NTSC TV.

In fact, I'm using a 74HC4052, and compare the signal from PIN7 of the motherboard and a signal set with the switches. From that, I select between 2 circuits with 2 distincts crystals (3.57Mhz and 4.43Mhz). I'm also doing this because the circuit has to be the shortest possible, and with that you can place the switch wherever you want in your console.
Also, the mod will be reversible: juste remove the board and place the CXA on its original place.

I hope this is OK because this is just a theory I came up.

I'm still waiting for some parts in order to build my prototype. I already know that a capactior next to the CXA on my VA3 will get on my way.
Here's the schematic and the board design from Eagle. The board fits in a 5cm square (2 inches)




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For the switchless Mod, I'll do first the Megadrive, then MegaCD. I still have to find a clean plugable solution for the 32X.

I'll follow the tutorial from Dforce3000. It's using a 16F630 and is an adaptation of the Saturn Switchless mod.

But I wanted to used a RGB led and have separated colors, but the mod and the PIC Program use only 2 pins for a bicolor led.
At first I wanted to add another output on the program, but I cannot figured out to do it. So I decided to use a 74LS00 to have my 3 signals.

Also it seems you need to cut some trace around the swith button, and I'm not a big fan of that since it could be hard to revert this change. I'll try to make a board and replace the reset switch.

I've just finished the schematic on paper, I'll post the clean Eagle version later.



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I'll update as often as possible.

Thanks for reading. Comments are welcome

 

Here's the final result:
Don't laught too hard on my accent:

[video=youtube_share;mOY_44WACEU]http://youtu.be/mOY_44WACEU[/video]

Here's the links and the files I used for this mod:
DForce3000:
http://www.dforce3000.de/?uid=12

Mmmonkey:
http://www.mmmonkey.co.uk/console/sega/md1-switchless.htm
http://www.mmmonkey.co.uk/mcd/index.htm
http://www.mmmonkey.co.uk/console/sega/32x-switchless.htm

Files I used:
https://www.dropbox.com/s/0qlvr2iglw40chi/mega_drive_switchless_multinorm_16f630_d4s.tar.bz2 ?dl=0
https://www.dropbox.com/s/b1o8gzmtrtvlemh/MEGACD_Switchless.7z?dl=0

PCB I made:
https://oshpark.com/shared_projects/bBIxsMHm

 

For my switchless mod I didn't solder it in quite the same ways as have been described - they cut some track and solder to some tiny little thing on the top, which I'm not a fan of. I think I found an alternate point that I could solder through a hole to the underside of the board and isolate it on the bottom side (similar to the language selector). Seems a bit more reliable a connection to me, and very easy to revert - just bridge the bit that's isolated again. I can possibly post some pics if interested.

If your objection is something else then never mind

 

Yes, pretty please. Any alternative is good to see.

 

RE the two crystals, won't you need a 3.56mhz crystal instead of 3.49mhz? IIRC the CXA1145 needs 3.56mhz fed into the chip via a couple of components to generate the correct colour channel for composite/s-video/RF colour.

Kudos for allowing the circuit to be disabled too - have found turning off add-in oscillators makes a difference when hooking up a machine via RGB (less noise).

 

Ha yes my mistake, it's 3.579545 MHz indeed.

EDIT: I don't know why I wrote 3.49. > I wrote 3.57mhz on the board and the schematic -_- .

 

Haha, sorry about that from my end - I should have paid closer attention to your schematic!

 

I would like this as well and is there such points on the model 2's? I have my own switchless board and if I don't have to cut traces that would be good.

 

Ok, I've finally all the pièces. I haven't bought the PIC programmer yet, since I had to buy a new fridge and that wasn't part of the plan :/ .
I'll build the proto of the video board by the end of the week-end.

I have also made a V1 of the switchless board.
I had to make a weird circuit with a 74LS00 in order to transform the output for a bi-color led into a RGB led.
I wish I had some more advanced programming knowledge and used one more output of the PIC, but I couldn't figure it out.

The small part on the bottom will replace switch. I still have to take some measurements and really find a way to not cut any trace.

board:

schematic:

 

I made a monster :




Seems good from what I tested. I need to test it thoroughly. It was a pain to make. It's horrible. I hope this will work.

Next step:
- be sure to this "thing" is functionnal,
- some measures on the MD,
- find a good solution for the reset button,
- make the PIC board,
- Once both prototypes are working, command to OSH Park some clean final PCB.

 

Here are a couple of pics of how I did the switchless mod with respect to the reset switch (MD2 VA1.8, btw).

Before:


After:


Parts-side:


Basically, I used kynar wire (light-grey in the 3rd image) to poke *through* the hole on the parts side (it is NOT soldered there), then routed it to a solder hole UNDER the reset switch, which I had isolated by cutting a box around it (in grey rectangle). This wire connects to pin 8 of the 16F630 PIC (reset out).
The other (orange) wire is just soldered from the top down through the solder hole a bit lower down the board (orange rectangle). It connects to pin 13 of the 16F630 PIC (reset in). I think I had to scrape a bit of the solder pad off there to give a better solder joint.

In this fashion, I have pretty solid solder joints, and also if it needs to be reverted, simply take off the wires and then bridge some solder where I chopped around the reset-out hole in the grey box (which is really easy to do, and would be a very solid connection).

I should probably mention I used dforce3000's code in the PIC - since it's actually specifically for the MD mod. Find more details at http://www.dforce3000.de/?uid=12 .

Observant folk might notice the 'before' board is clearly not the same as the after - very good. It's enough to give the idea though. And you can poke the kynar through any one of the holes which ARE open on your board that is near enough to the reset switch.

HTH


also, just realised the OP's av is of Kamui Senketsu from Kill La Kill, nice

 

Thanks fluxcore. As mentionned, I'm also using dforce3000's mod.

Unfortunately I'm making my mod on a VA3 which has a different layout. I took some photos and measurements for the switch.
Also, I forgot to add an 5k resistor on my switchless board (since VA3 has an active-high switch) and a 100nf between +5v and ground just to be sure to don't have any noise.

And Yes, it's Senketsu, a pixel art sprite I did for an side-event of a french convention (the Stunfest)

 

Ok so I've tested the board by attaching a USB plug and a switch to simulate the behaviour of the NTSC/Pal line.
Everything seems fine. The only way I found to see if the correct crystal's circuit was called each time I'm changing the switches is by measuring the resistance between a circuit and the output pin and see if it falls to 0 when selected.

It works but I have a doubt that the non-selected circuit will generate some noise since I had a really high resistance on them whereas I was expecting nothing.
To be more clear, the selected cuircuit has a resistance of 0, but at the same time the other circuit has a realy high resistance.

I think I'll totaly isolate each circuit just to be sure. Right now they have common ground on the resistors and trim capacitors, I'll make closed cuircuit and add 2 diodes before joining them on the common ground.

Is it a good idea?

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On an other subject, I'm puzzled by the switchless mod and the reset button. After taking pictures and look at the Genesis' schematics, I still don't understand how to make it works on VA3/VA4 with an active-high reset.
This is what I understand so far:

The PIC takes place between the "switch+510k pull-down resistor" and the reset line.
But on the PDF of Dforce3000 it says that I need a 5k pull-down resistor. Why? The 510k is not enought? and where should I put it?

I tried to compare with mmmonkey's mod but it seems way to complicated.
I'm starting to think that a NPN transitor will be the simplest solution and make something like that:
Switch --> NPN ---> PIC-in
then
PIC-out ---> reset line (using the 510k pull down resistor as welding point)

Any ideas?


Edit: damn the more I read my post the less I find it understandable. I'm really sorry for my poor english.

 

While I'm still investigating on those subjects I've tested a part of my switchless board:




Yay RGB colors
The 2 wires on the pictures will be on pin 5 and 6 of the PIC. When one of the wire is "low" logic this will change the color. Technically, both wire on low will just set the led off, but I don't think the PIC program can enter in this state (only H/H - L/H - H/L).


Nobody can help me about the adding the diodes and about the reset switch?

 

this is some real cool stuff ,,,enjoying this !

 

Thanks shark, I was starting to feel lonely.

While I was looking on the switchless board, I realized I made something way to complicated.


Only one gate, and bonus:

A fourth color (cyan). So if one day the PIC program is updated for a L/L state (like JAP 50Hz) the board is ready.

But now I'm stuck with the 74LS00 and 3 other gates for nothing.
I search for a 74HC1G00 or 1single 2-input NAND gate but I found only ICs in SMD and no DIP. :/


Nobody wants to help me about the reset switch?

 

Could you show all the pictures of each install wire? it looks like you didn't make the cut where your yellow wire is so I'm wondering if you cut anything on the bottom of the board connected to that via and the other wires as well.

Also could someone edit dforce3000's source so the pinout matches that of mmmonkey's mod, I made a few pcbs for that mod and would hate to throw them out since the pinout isn't the same for this mod. I did try editing it myself but shit experience coding for PICs but if someone could take a look at my code or make the changes I would be grateful. Here is the current pinout of dforce3000:





Seb's code:




My edited ASM file:
http://www.mediafire.com/download/d4a1kw8pa8sac3y/Genesis_Switchless_Mod_ASM.rar

 

The yellow wire is connected to the isolated language selector pin on the ASIC, if you look at the underside image with the orange/grey rectangles, off to the right of the grey box is where the yellow wire attaches (you can see a silver mess where the isolation cuts forming a square are, the inside is soldered and isolated from the surrounds). I didn't do a particularly *clean* job of isolating the solder hole from the surrounds on this one though. I didn't highlight it because it was irrelevant to the reset switch part.

I don't like cutting the trace on the top-side of the board and soldering to that, seems very fragile to me. I prefer soldering through to the underside like this instead, even if it means a lot more cutting.

I feel like noting this was the first time I'd tried the switchless MD mod, and also that this board was a repair job anyway, so I wasn't particularly concerned with being tidy with wires or cutting the tracks out >_<


As for the OP's reset switching question, sorry, not sure how to help you with that one.

 

Edited my post above with some extra info if you or anyone could help. Also what did you for the other wires like the video selector wire? did you do the same with cutting something on the bottom of the board where that via connects to?

 

Daily update. I've start to redo the video board. I'll deport the switches and make a "remote" which you can place anywhere in your MD.


It's a mess right now. I'm trying to make the smallest board as I can.

Also I think I have an idea for the switch, but this will lead to remove the 510k CMS resistor from the motherboard and put it elsewhere.
This could be a good solution and provide me some welding point to the Reset line.
I'm still puzzled with the 5k resistor mentioned in the Dforce3000's PDF.


@Helded: Sorry pal but I've no experiment with PIC (yet) and programming (only some basics on some script languages). If I had I would gladly help you and made a modification for using a third output on the PIC rather than using a additional gate for the RGB led.