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

Yes, if I'm not forcing myself to hide it I sound pretty much like that (in fact every french speaking English sounds like that).

 

Sega 32X Switchless: done!

Fiewwww that was a real pain to align the 2 connectors.

On the MegaDrive side:




I've already removed some of the glue (I don't have a pic) and I also had to replace it a bit higher.

On the 32X side:


I used some electric tape to isolate the wire after that

And the connection on the 32X:


Since I don't have any Pal 32X games, I used my Mega Everdrive and yes it works. Some games like Metal Head works like a charm.

Next stop, the Mega CD.

 

Finally, I've got my order from buyICnow.



Some stuff for the Mega CD and for Snes reproduction carts .

 

Let's continue this mod!

So after my pathetic yet successful cart mod, I've continued the last part of my switchless mod: ce Mega CD.
Removing the old bios.


Add 2 more lines in the "U" connector


The socket and the new bios, ready to duty.


Does it work? Well, no. I've tried to make my own multibios with each region free bios (and columns for fun). But it's doesn't do anything.
Since those chips are 27C4096, it takes 15mn to erase them, them redo a test.
Looks like I'm really bad at programming stuff.

I'll update when it is working

 

So, after erasing the EEprom and redo the multi bios (a correct byteswap) it works!
Here's the baby in place. I also changed the battery.


US:


Jap:


EU:




and just for fun, I've hi-jacked my board to see if Columns from the MegaCD bios is working:


I'll change the colors of the LED for each region in order to have a full japanese console on the outside.


It seems I've also some grinding noises from the Mega CD, so I might have to open it up again. :/.


But the mode IS DONE! Hurray to me!



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Also I've worked on the video board, and I think I've come up with a good solution.

 

So, after a lot of thinking, I might came up with a ideal solution for my video board.


My board has 3 positions and is based on the signal sent from the console to pin7 of CXA and on the signal from the small region switch:

a) OFF: gate A and B are the same signal from the console, so always true on the 74HC5042. So it use Y/X0 and Y/X3 gate.
b) Patch: Compare A from the console and B from the region switch. If it's the same signal then true, if not, then uses Y/X1 if the switch is set in NTSC (GND/+5V) or Y/X2 if PAL (+5V/GND).
c) Override: A and B are always different, so it force the Y/X1 or Y/X2.

The probleme is when you want a 3.57Mhz subcarrier for the colors in PAL, it doesn't work (well, maybe in Brazil).
On the contrary, you can have a 4.43Mhz colors subcarrier in NTSC (PAL60Hz or NTSC 4.43).

Since my board giving a better signal than the original subcarrier, I wanted. So I need to modify my board for:
a) OFF
b) Patch always with correct colors subcarrier (only NTSC-60hz and PAL-50hz)
c) Override, allows NTSC-50hz and PAL-60hz


After scratching my head for a while, I realized that my board is actually doing its job.
The problem was the remote.
The main issue was when patching, if the signal A and B where the same, the gates are on the original subcarrier.

I needed to have always the invert of what the console is sending.
If the console is sending me a NTSC on pin7, I need to have a GND an use the gate Y/X1.
If the console is sending me a PAL, I need a +5V for using the Y/X2.

The difference with the override that the signal is still driven by the console.

So I came up with 2 solution using an inverter: a 74AHCT1G04 inverter, and a NPN transistor.




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I don't think I'll order the new remote now. I'm going back to France for holidays in august.
Also, I need to order a new video board compatible with VA3/VA4.
Since I have other bunch to order to OSH park I'll eventually order everything to have them when I go back.

I'll make some update on the firsts posts to regroup all the info I gahtered from this mod, and upploading the files I used, etc.

 

Small update.

I've made some test in order to see if my idea of the new remote was ok.
After a few hours, I realized that with the 32x attached, my board won't work.

I finally understood why:


The 32X has its own Crystal Subcarrier.

So I have to make a video board for the 32x and NOT for the Megadrive. All my efforts were useless.

I'll still order the new remote and see if everythings is ok, but I'll order the board for the VA3/VA4 later.
Now I have to design a board for the 32x and eventually I'll the same thing for the Megadrive model 2 after some prototyping.

 

Ah yes, in retrospect that is certainly something you'd need to account for. It's pretty cool actually that by using a 32x you can avoid having to fix the colour on a 50/60 modded MD through composite. Doesn't help you when you're trying to provide all the possibilities with colour encoding though...

 

From what I understand, the 32x give a better image, but for me it's now clear to me that's due to the fact that it uses a real NTSC color subcarrier, and not the average value derivated from the main oscillator of the console.
As I saw on my Megadrive, with a real 3.579545 mhz crystal from my videoboard, the image is way, way better. The 32x is doing the same thing.

My only problem is the space inside the 32x: making an additional board will be tought. I still have a spare "line" from my switchless board to the 32x, but I'll eventually make an auto-patching mod.
Maybe if I design a surface mount board I would be able to make something small enought to fit inside, but I don't have a rework station nor twizzle solder...

 

Depending on the size of the SMD components a regular fine tip soldering iron works fine, also you could design a board that connects to the points you need then have a ribbon connector with ribbon go to the Genesis/Megadrive since it has more space to house your board with the components.

 

I've just ordered a surface mount board CIC + IGR for my Snes



That will make me a good training.

 

That should do well for some practice,just make sure the PICs are programmed correctly before soldering as trying to remove them later on without a hot air rework station will prove very difficult.

 

Yeah I know, I had some bad experiences with a 29L3211 and my repro of Star Ocean. I still have 2 16F630 in DIL-14 so I'll prepare all the wires inside the Snes, and try before the code with a proto board.


Also, I've made a first the schematic of what the 32X video board should be:


I copied the original design from the 32X schematic. Since some values of the resistor/capactior are different from NTSC and PAL, I saw 3 points do bypass in order to have an alternate cuircuit:
- on pins 11 and 12 next to the IC12 videochip,
- after the resistor 40 next to the transitor TR2, which leads to pin 10 of the IC12.

I'll use a 74HC4053 ( a triple 2-channel analog multiplexer) and see from PIN32 if it's a +5V (NTSC) then use the original circuit (nY1 to nZ) or if it's a GND (PAL) signal then switch to the replacement one (nY0 to nZ).
Unfortunatly with this design, this board will work only work for NTSC 32X. Ill add an inverter or a solder point for make this design compatible for PAL 32X too.

 

So I've updated my design:



The components on the board has to be the opposite of your 32X. If you have a NTSC 32X, you have to make a PAL board.
I've used the same name as the original board.
In order to limit the number of cut traced on the 32X, you'll have to remove the resistor R40 and R41 from the 32X, and resolder them on the board, so you'll have some solder points.
Also, since the 74HC4053 needs a GND signal to use the board circuit and +5V use the original circuit, you have to invert this signal for PAL 32X.

But there's another problem: after looking toroughtly the schematic of the 32X, I saw something else: the value of components on Yout/Yin and Cout/Cin are different between PAL and NTSC : inductors, capacitors, resistor they are all different. Their values are not so different, but still.



So there's my concern:

If I change the circuit of the Crystal subcarrier, will that make Yin/ou and Cin/out wrong? If not why should I be concerned of making a board so complex, and just making a switch on the Crystal?

The more I'm trying to make an universal input, the more I feel all my effort are useless. :/

 

Hi everyone, sorry for the lack of updates. After 3 weeks of vacation back in France, let's go back to some electronics.

So I received my 2nd order from OSH park with the new remote for the Videoboard (amoung some other stuff, like my IGR+Super CIC board, Super CIC key for Snes repro Cart and TSOP to Willem adapter)

And.... there's a mistake in my design: I've inverted two poles of the 2P3T switch. :/
The good news is when they are in the good order, it works: I finally have a normal behaviour: the patch mod will automatically use the correct subcarrier, the Override force the subcarrier.

I've already corrected the design, I will order later the new-new remote.

Also, I've bought a reworking station, so now I'm able to do SMD stuff

 

Good stuff!

 

Ok so I'm starting to think that I'm inverting the same signal twice and/or mixed up the gates in the 74HC4052. Even if now I have the good design of the remote for the first videoboard I made, I'll have to go back to the drawing table to see if I'm wrong or not.

Also, I've perfomed a switchless mod on a Genesis 2 VA 1.8 with the same board I used in mine


It works fine. I now have to make a prototype of a videoboard for the Genesis 2, which has the particularity of not have a Crystal driver. I saw here 2 methods, and got the design done for both.
If one of them works, I'll order from OSH park with the new-new remote, and the 32X videoboard.

 

Quick update.

From this thread: http://www.assemblergames.com/forum...ive-2-PAL-60Hz-color-fix-with-a-2-pin-crystal

I built a proto board with the 74HC04, but unlike Da bear, I didn't cut the trace to the R61, but I've removed the resitor, added a 10k on my board (which is the value of the R61) and used one of the solder point of the R61.



That works! So by using my own work, I will be able to make a videoboard for the Genesis 2 too.

I haven't test the solution with the 12C508. But since this one is working I will stick with it.

 

Alright, update time. I finally recieved my order from OSH with the 32X board. I didn't expect it since it still in "process" on my OSH's profile (meanwhile I'm sill waiting some other stuff set as "expedited", like the "new-new" remote for the Genesis 1 board)


Unfortunately I didn't receive yet the 74HC4053 I need.

I've also received the board for the Genesis 2

and made some modification since there are some flaws in my design.

I had to totally close and isolate the NTSC and PAL circuits, and add a diode on the "on/off" jumper in order to avoid some wierd behaviour: I use a gate from the 74HC04 as an inverter, but it seems to interfer on the "video line" (SW3/SW4) from the console.

Tested in a Genesis 2 VA1.8, it works! But I didn't find a good place to put the final board, and had to glue it on the side. I'll take some picture tomorrow.

 

SO what exactly does this last board pictured do? does it change the region with appropriate frequency from those crystals? Sorry if this seems obvious but the thread hasn't been updated in some time and I lost track of the progress. Also OSHPark has a new speedier fabrication service but pricey that will get the boards fabricated and ready to ship in 5 days.