Proper brightness control for Sega Nomad screen mod

After playing my Sega Nomad for a little while with my modified lithium battery I started to become quite annoyed at the screen quality, in particular the edge bleeding and motion blur. I'm sure that anyone with a Nomad will sympathize with this problem. So I've taken the plunge and am performing a screen mod using one of the readily available 3.5 inch $20 ebay screens, however some screens are better than others, and after some experimentation I realized that some screens display an annoying AV in the top corner for a few seconds, while others do not, some screens turn off during black screens while others do not, and some screens require more voltage than the battery can provide.



From the pictures you will be able to see the screen that I decided on, it came as only the LCD panel and driver board wrapped in polystyrene, you will be able to find this exact screen on ebay. The problem with this screen is that it likes a slightly higher voltage than the NiMh battery can provide, however with the 7.4 lithium ion battery mod there is virtually no waterfall effect over the discharge cycle, so it should keep working right up until the end (at least 5 hours by my maths). I did however bypass the shockley protection diode at the input to the screen as there is already reverse polarity protection at the nomad power socket, and shockley diodes to provide a little bit of loss.

The next problem was getting a method of controlling the brightness, I isolated the brightness control to a 3.3k resistor on the top left hand corner of the board. This is actually adjusts the level of backlighting intensity as opposed to adding or subtracting voltage to the video signal like some other screen brightness mods. When the resistor pad is earthed out, the screen becomes brighter, when disconnected the screen becomes darker. By placing a trimpot in place of this resistor it is possible to have full brightness controls. The problem is that the trimpot in the nomad is 47k and we want about 4k across the sweep........ so i went hunting through my junk box and found a thumb-wheel style volume control trimpot from an old discman, this was a dual sweep trimpot as it used to control left and right channel volume. Each channel of this trimpot had a 10k sweep, so by running the two channels in parallel I could create my 5k sweep. You will need to ream out the two mounting points on the nomad motherboard as the trimpot is a few mm wider, and has an extra leg. The extra leg doesn't need to go through the motherboard and can just stay horizontal above the board as it will be soldered to the pin directly beside it for support and to create our parallel resistance in the trimpot.





Here you can see the new trimpot mounted to the motherboard, there are a few SMD resistor that need to be removed on the reverse side in order to isolate the trimpot from the old circuitry.


I decided to use the old screen housing to mount my new LCD and driver board in, it required a little bit of dremelling as the new LCD was a little fatter than the old, and then a little hot glue to hold it, usually I'm not a fan of hot glue, but in this instance it was only holding it in place as the screen was already secured with the metal top plate.










I used a little bit of cloth tape to insulate the top of the capacitors against the Nomad motherboard when it is all assembled. Note that I am yet to connect the wire for the brightness controller, I did this last as it is quite delicate and I did not want to stress my solder joints and circuit board tracks while testing.





Now it's just a matter of connecting up the power and video to the screen and putting it all back together





It all looks completely stock, even the brightness controller works perfectly across about 3/4 of the sweep, which is actually better than on the original nomad screen as it would wash out completely at about 2/3.

 

Nice job. I like it.

But what about that lcd? Every one that I've tried that looks like yours has the double blurred line about 1" from the bottom of the screen.

Like this :

 

I've never even seen a hint of that on my new screen, are you sure that when you removed the old nomad screen none of the terminals on the motherboard or ribbon cable shorted? It looks like it could be a problem in the nomad as opposed to the screen. A good way to test the screens is to plug them into a SNES, 64 or whatever else you have laying around and check the image quality. I used an old SNES as my test bed while I was probing to find the brightness adjusting points and gave it a good soak test before putting it in the Nomad. I would try a different video source and see if it's the screen or the nomad.

 

Oh yea I remember having trouble finding the good screens for a Nomad! I learned fast (after the first) to test them first via an av cable plugged into the nomad.

The bad ones became chrissy stocking fillers (since i didn't take them apart).

I like your idea of the brightness wheel, unobtrusive. Myself I just installed the menu buttons and in place of the brightness wheel I installed the region switch. Unfortunately I sold that Nomad and need to make another one lol!

 

Could you post a link to the seller of the lcd? Also could you post what you did to the nomad mobo and the lcd controller board with some notation?

 

After some experimentation I found this screen to be excellent.

http://www.ebay.com.au/itm/261302842800?ssPageName=STRK:MEWNX:IT&_trksid=p3984.m1497.l2649

As for the Nomad motherboard, all I did was de-solder the old LCD screen and cover the terminals with a strip of tape to avoid shorting, I then removed the old brightness trimpot and reamed the two mounting holes at the edge of the motherboard slightly with a drill so as to fit the new slightly wider trimpot. It doesn't matter if the body of the timpot is earthed, so you can solder it directly to the motherboard earth track in the event that you ream past the original solder pads. On the reverse side of the board under the trimpot you will see the 4 trimpot terminal holes, 2 of these holes (centre two for memory) are connected to nothing while 2 (outer two) are connected to a small SMD resistor. When you look at the board you will immediately see the two tracks running from the terminal holes to the two resistors, its very easy to spot, simply remove the resistors and your trimpot will be completely isolated from the old circuitry. Because the trimpot that I used had 5 terminals, I bridged the extra pin to its neighbour seeing as I was running the dual gangs of the pot in parallel, this can be seen in the photo. Yo can solder the screen brightness wires to either the top side or the bottom of the board depending on what you think looks neatest, just remember that the outer two pins on each side of the pot must be bridged in order to give you a 5k sweep.

As for the power connection, I simply soldered the positive wire onto the track leading to the on side of the switch (once closest to the centre/screen) and my negative terminal to the shield pin (outer pin) of the DC socket. As for the video, the pin you want when looking at the back (solder side) of the motherboard coming off the AV socket is the second from the right pin on the lower row. It's easy to identify as it has a little unused solder pad below it. I just realised that the picture is a little blurred, but if you look at the yellow wire you can make out that it's connected to the second pin at the right on the bottom row of the AV socket, if in doubt you can always prod your video wire on the pin that you think it is and check for signal, there are no dangerous voltages on that connector, only audio and video, so you cant hurt anything

As for the LCD controller board, all you have to do is remove the 3.3k resistor at the top left of the board and solder little wires onto the pads where it once was then connect them to your new trimpot. If you look at the before and after pictures of the driver board and where I soldered my wires you'll see exactly what resistor it is. That's the only modification that you need to make

 

I'm the inventor of the Nomad mod, so I've been doing the screen mods since 2008. So I don't make mistakes like shorting out any pins

At first all the 3.5" screens worked fine. Then the sellers all started using a different video chip. They worked fine with any system other than the Genesis/Nomad. With the Genesis/Nomad you get a double blurred line at the bottom of the screen. It's only noticeable with text. And since most people only mod one Nomad they usually don't notice it.

For some reason you can't just test them on an N64 or Snes as they look fine on those systems but not on the Genesis/Nomad.

I have bought over 15 different screens from 15 different sellers in the past year and they ALL have this problem. I finally found last year a suitable screen , but it is a lot harder to install as quite a few parts have to be re-located.

I have several screens that look just like yours and they have the double line problem. That's why I was wondering if maybe you just haven't noticed it.

 

What would be a good game with lots of text to check for the double line problem? It's very odd that the Nomad would have this quirky reaction to the screen, I'm now quite curious to find out why. I'm wondering if the double line problem occurs with both NTSC and PAL games, it might give a clue as to whats going wrong in the signal processing, it certainly looks like a de-interlacing problem, so if I find mine to be doing it I'll try find a solution, it would almost certainly be a signal noise problem from the nomad, maybe interference from the graphics processor.

Thank you for you original mod, it gave me the inspiration to do mine, without your guide I would have probably never thought about a screen transplant. After playing it these last few days I really do believe the Nomad to be one of the coolest handhelds going I'll check this screen issue and try to create a fix so that you can use the screens again, they seem to fit really nicely.

 

I don't have any Pal games to test for the problem. So it might be NTSC games only. I'm not sure.

I use RPG games to look for the double line. Subtitles show it really well.

It would be nice if you discovered the problem. The screen/controller only 3.5" is the perfect size and the easiest to install so it would be nice if they could be used again.

 

I was getting a little bit of a distortion in my text, after a little reading I suspect noise on the sub-carrier sync line, so I'm replacing the the video encoder with one that doesn't require an external sub-carrier pulse, this will also mean that I can get a PAL output and PAL60 when playing imports. The chip I'll be using is the AD724JR as it's pretty simple to implement and is happy to run of RGB and CSYNC. the chip is only $3 from ebay and has 16 pins, so it should be very easy to work with and cheap if something goes wrong. Stay tuned, the parts are in the mail!

 

PAL 50 Nomad modification

after some fiddling around I managed to modify my trusty old nomad to output a true PAL 50 so that I can play my Australian and European games on it. This was done by firstly changing the pins on the CXA1645P/M so that it outputted PAL colour this was done by changing pin 7 and pin 18. Pin 7 needing to be lifted and earthed while pin 18 is lifted and connected to ground through a 16k resistor.



This will Set the CXA1645P/M to PAL mode however there is a catch, the colour subcarrier frequency is still NTSC and as such the image you get will be black and white. To solve this I removed the NTSC frequency crystal oscillator from the lcd driver circuit and replaced it with a PAL 4.4336mhz subcarrier crystal.



I then tapped from the crystal occilator output and ran it into the lifted pin 6 on the CXA1645P/M.



The Nomad will now have perfect PAL 50 with colour.

 

Obviously I changed the region and frequency jumpers to suit my region.

 

Nice mod!

 

Done the same/similar to the old Nomad but I added the oscillator. I actually like your way better.

 

Well, that should just about cover how to modify the Nomad with a new screen, working brightness controller and true PAL 50 for all those European and Australian folks out there. I have not noticed any problems with text being interlaced or distorted either when running NTSC or PAL, so I'm thinking it's luck of the draw a lot of the time with those Chinese screens and how well they display. If anyone has any problems or cool ideas they would like me to try I'm all too happy to help, just drop me a line.

 

Have you done the reset mod? Using the start + mode button and an OR Gate to cart slot B2. Handy for those pirate carts that use reset to select the game.

 

Hi torben. I tried your color mod with my nomad, becaus i only get strange pictures on my LCD but i can't get it working as you can see in the following pictures



without the mod i have black/white pictures with vertical scanlines on NTSC and rainbow colors on pal

Do you have any idea whats going wrong here ?

 

[FONT=Lucida Grande, Geneva, Verdana, Arial, Helvetica, sans-serif]The first thing I would ask is what video frequencies are you trying to run, this mod only really works for PAL50 as my screen was not happy outputting NTSC50. Were you getting a good solid picture before you changed the motherboard frequency jumpers? I suspect that maybe one of the pins has not been lifted away cleanly from the motherboard, most probably sub-carrier syc pin 6, as the original sub-carrier frequency may be interfering with your new one.
Is the frequency of the new crystal correct too, remember you need to change it to the pal sub-carrier frequency. It is also essential that[/FONT] pin 18 is lifted and connected to ground through a 16k resistor for the video processor to output a PAL colour profile. I didn't actually lift mine, but instead just removed the surface mount resistor running to the pin because I was lazy, this works too and saves lifting a pin.[FONT=Lucida Grande, Geneva, Verdana, Arial, Helvetica, sans-serif]
The fact that you are getting some colour is promising, remember that once you do this, you will be locked to playing things in 50hz PAL, I am quite happy being stuck on PAL50 as my whole collection is Australian, but if you are wanting to play american/jap games then you might need to so some elaborate switching.
I did actually buy one of these [/FONT]http://www.alibaba.com/product-detail/PS2-NTSC-PAL-CONVERTER_361448489.html [FONT=Lucida Grande, Geneva, Verdana, Arial, Helvetica, sans-serif]and was tempted to trim it down and put it inside the nomad somewhere, if you did that it would display anything you threw at it. All it requires are the three RGB signals, the video composite for sync, and 5 volts, all of which the nomad has, so you could actually wire it up and test/run it from your genesis/nomad using only the AV port for starters to see how it performs. It will basically take the RGB and composite sync, combines it and output PAL50, fitting it inside the nomad might be tricky.

Anyway, let me know how you go, I'm all too happy to help.
[/FONT]

 

Anyway this can be adapted to a Game Gear?

 

The Game Gear is a different kettle of fish all together seeing as it never had a composite video output to begin with. There are a few boards out there that provide composite and component output so that you can use a modern LCD display.
http://segaage.com/forum/messageview.cfm?catid=48&threadid=63769
There are some very good pictures of the mod on there, it's not too hard to install by the looks of it, but will probably cost you a little more in parts.