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  • Joined: 19 Aug 2011
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Master System II AV mods
Post Posted: Mon Oct 09, 2017 11:20 pm
Hi,

Want to pick people's brains, get some information and share experiences regarding AV modding MSII consoles.


PAL MSII console
Sony CXA1145
CRT TV


I will briefly point out that my console is 50/60Hz modded and that I've also wired up a toggle switch to be able to alternate between PAL/NTSC output.

RGB mod:
No issues here. Just wired straight from the appropriate pins of the CXA1145 to a panel mount 8 DIN socket, same pin arrangement as original MS1 so I can use standard MS1/MD1 cables.

S-Video mod:
Needed to use a transistor to prevent sync/screen tearing issues on brightly lit screens such as the yellow background in Alex Kidd MW title screen.

What worked best for me is:

PIN15 (CHROMA) -> 75 Ohm resistor -> Chroma pin of s-vhs socket

PIN16 (LUMA) -> Transistor BASE
Transistor EMITTER -> 75 Ohm resistor -> Luma pin of s-vhs socket
Transistor COLLECTOR -> +5V

I didn't find a need to add a capacitor to the chroma line.

By using a 75 Ohm resistor on the Luma line jailbars are eliminated.

I experimented with all the different methods I could find online, what I wrote above yields the best results for me. Natural non washed out colours, no jailbars, stable image on all games.

AV mod:

Regarding audio, I don't feel that the 10uF capacitor is necessary. I obtain audio from PIN9 of the CXA chip which already outputs a buffered audio signal. Audio is crystal clear and at normal volume.

Video output is where things get interesting.

Stock standard mod appears to be:

PIN20 -> 75 Ohm resistor -> 220uF capacitor -> RCA socket

Works great however weird video glitches can occur at certain points in certain games. E.g. some levels in Alex Kidd MW, The Ninja and Sonic.

Screen flashes purple and drops out intermittently, sometimes very briefly and at other times for longer durations.

It doesn't happen continuously throughout the game. Title screens and some areas of the game display fine 100% of the time, seems to be certain colours or amount of fill colours that triggers it. Some games never exhibit the problem.

I noticed that upping the 75 Ohm resistor to a higher value, somewhere in the range of 120 to 150 Ohm, will completely eliminate the issue. This has the drawback of dimming the screen and over saturating colours.

Altering the capacitor value doesn't change anything. All that I noticed is that you want to use at least 10V.

I traced out my Master System 1 console which has the same video chip:

PIN20 -> 75 Ohm resistor -> 100uF 10V capacitor with a ferrite bead connected in parallel -> DIN plug output

Perhaps the ferrite bead is the missing component and will make all the difference?

Using a transistor greatly improves the situation however in Sonic some very minor video glitching can still occur.

PIN20 -> 75 Ohm resistor -> Transistor BASE
Transistor EMITTER -> 75 Ohm resistor -> RCA socket
Transistor COLLECTOR -> +5V

This provides a great stable image, natural colour balance and brightness levels. The aforementioned video glitching is greatly reduced, it seldom occurs, but can still creep up in games such as Sonic.

I've googled around and it seems to be a common issue but not one that's talked about much. Perhaps people don't notice it or dismiss it as it only occurs in certain sections of certain games. There's a post about it on these forums somewhere, will need to dig it up...

So that's my findings and where I'm up to. Anyone have anything to contribute?
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Post Posted: Fri Oct 13, 2017 11:10 pm
Im wondering if your TV is the problem here Frank?

Have you tried a few different TVs?

I have always hooked up the lines using a 75ohm resistor and a 470uF capacitor, as per Sony recomendation for their CXA1145.
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Post Posted: Fri Oct 13, 2017 11:28 pm
I don't think it's my TV.

I have since created a circuit that works perfectly with no glitching.

In my testing I noticed a relationship between the glitching and ground points. E.g. pending on where you grounded composite video the glitching became better/worse.

I did notice that on some MS2s there's a black wire running from one of the ground pins of the cxa1145 to a cap. Looks like a last minute factory 'fix'. Maybe this is related to the problem.
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Post Posted: Tue Apr 17, 2018 6:27 am
@MasterGear78

Here's the schematic for the composite video mod I use in MS2's. It's the only way I've come up with to reduce glitching on certain TV's.

The capacitor should really be 470uF but 100uF or 220uF will work if that's all you have on hand.
MSII-AV2.png (21.06 KB)
MSII-AV2.png

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Post Posted: Tue Apr 17, 2018 6:49 am
Frank_fjs wrote
@MasterGear78

Here's the schematic for the composite video mod I use in MS2's. It's the only way I've come up with to reduce glitching on certain TV's.

The capacitor should really be 470uF but 100uF or 220uF will work if that's all you have on hand.


Thanks very much, I'll give that a try. Where do you usually take 5v from?
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Post Posted: Tue Apr 17, 2018 6:56 am
I grab it from the CXA1145. Pin 19.
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Post Posted: Tue Apr 17, 2018 7:00 am
I tried the A/V (composite?) mod last night - signal from pin 20, through 75ohm resistor, 220uf 20v (tried a 10v too) and the image had interference on it, looked like horizontal bars of fuzz rolling up the screen. Tried a few things and got the same issue - I also noticed the purple flickering mentioned earlier.

I'm going to try your 75ohm - 420uf - 75ohm later and see if it works.

A couple of questions - why does the transistor make a difference in your circuit?

Also... I looked at the schematics and the video out from pin 20 goes to the RF modulator - why do people not tap the video signal from pin 2 going in to the modulator?

Thanks for the useful info so far :)
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Post Posted: Tue Apr 17, 2018 7:06 am
I noticed with 150 Ohms resistance all problems were resolved. The issue with using the higher resistance is that the picture becomes too saturated.

So to maintain the image colour/brightness/contrast balance and stop the interference/glitching, I use 2 x 75 Ohm resistors and use the transistor to boost the image to normal levels.

If you hook it up correctly you will be rewarded with a perfect picture. Perfect colour, brightness and NO glitching or artefacts under any circumstances within any game. Tested on both CRT and LCD TV's.
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Post Posted: Tue Apr 17, 2018 10:39 am
Certainly hope so! I've just redone the mod to make sure there wasn't any obvious errors. This time round i've gone pin 20 - 75ohm - 470uf - 75ohm - out and it still gives the exact same issues, the transistor is key it seems - I only omitted it as I'm waiting for some to arrive in the post!

Looking at other mods, like the famicom for example, it seems that having a transistor in circuit is the only way, most mods make use of one somewhere. I'm surprised anyone is getting any real success going down the cap + resistor only route from my recetn experience.
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Post Posted: Tue Apr 17, 2018 11:27 am
chunder_jacket wrote
Certainly hope so! I've just redone the mod to make sure there wasn't any obvious errors. This time round i've gone pin 20 - 75ohm - 470uf - 75ohm - out and it still gives the exact same issues, the transistor is key it seems - I only omitted it as I'm waiting for some to arrive in the post!

Looking at other mods, like the famicom for example, it seems that having a transistor in circuit is the only way, most mods make use of one somewhere. I'm surprised anyone is getting any real success going down the cap + resistor only route from my recetn experience.


I was able to almost eliminate the screen glitch by grounding the composite video jack to various parts of the MSII motherboard. I attached one wire to the side and one to the central pin of the voltage regulator chip and initially that seemed to fix it. Unfortunately the signal still flickers to black and white occasionally but it's greatly reduced.
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Post Posted: Tue Apr 17, 2018 1:37 pm
Quote

I was able to almost eliminate the screen glitch by grounding the composite video jack to various parts of the MSII motherboard. I attached one wire to the side and one to the central pin of the voltage regulator chip and initially that seemed to fix it. Unfortunately the signal still flickers to black and white occasionally but it's greatly reduced.


It does seem odd that there are so many issues getting composite video out.

Looking at the schematic, before the signal goes to the RF modulator, the signals goes from pin 20, through a 100uf cap, then strangely through a 75ohm resistor connected to ground? I don't understand that.

What is interesting is it then goes through an inductor which I presume is used to clean up the signal being sent out of the sony chip.

I still don't quite understand why we don't tap the composite signal from pin 2 of the RF modulator - its going through that smoothing circuitry. I did try it out but got quite a dim screen and it's beyond my electronics understanding to work out how to boost that signal if thats what it needs.

The frustrating thing on mine is that the RF signal is amazingly clear, the composite by comparison is hideous!
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Post Posted: Tue Apr 17, 2018 3:21 pm
The grounded 75R is acting as a voltage divider. It's not actually grounded both ends, the signal passes through one end while the other is grounded.

Strange that Sega used a 100uF capacitor. The CX1145 datasheet calls for a 470uF. Neo Geo uses the same chip, earlier units have a 220uF while they changed it to 470uF in later units.
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Post Posted: Tue Apr 17, 2018 4:51 pm
Only effect the smaller capacitor would have is possible brightness change between left and right side of the screen. Too small capacitor will result in loss of sync though. The bigger the better.
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Post Posted: Tue Apr 17, 2018 7:06 pm
It’s interesting that some people are saying that depending on where you ground the circuit gives different results - I’m not sure why that would be - all grounds are common aren’t they? So surely it shouldn’t make much difference whether you ground on the Sony chip, the ground plate round the edge of the board or elsewhere... should it?
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Post Posted: Tue Apr 17, 2018 7:18 pm
Ground is not equal everywhere, copper losses, inductances and currents that run though matter, especially for audio where you can get all sorts of buzzing noises from improper ground location.
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Post Posted: Tue Apr 17, 2018 8:31 pm
Ah... where is the ideal ground location on the sms2 then??
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Post Posted: Tue Apr 17, 2018 10:55 pm
Areas near power regulator but after any filter capacitors.
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Post Posted: Wed Apr 18, 2018 1:39 pm
Frank_fjs wrote

....

Using a transistor greatly improves the situation however in Sonic some very minor video glitching can still occur.

PIN20 -> 75 Ohm resistor -> Transistor BASE
Transistor EMITTER -> 75 Ohm resistor -> RCA socket
Transistor COLLECTOR -> +5V


Probably a silly question, can you clarify this arrangement?

In the quote there's no mention of the capacitor in the circuit, is that just an omission? Also the inference I get from this is that the transistor is in series with the 75ohm resistors, but in your circuit diagram a few posts later it appears to be in parallel, being connected directly to pin 20 and then outputting after the capacitor?
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Post Posted: Wed Apr 18, 2018 2:14 pm
Follow the schematic, ignore everything else.

The other stuff I wrote was just some early findings before I finalised things.
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Post Posted: Thu Apr 19, 2018 1:48 am
Frank_fjs wrote
Follow the schematic, ignore everything else.

The other stuff I wrote was just some early findings before I finalised things.


I tried the transistor boost and unfortunately it didn't seem to work for me. As soon as I boosted the signal back up the glitches returned. I even got occasional glitches with 150 Ohm resistance and no boost.

I've noticed some really strange patterns with this problem. It seems to be triggered by certain colors. It either effects the title screen on a game or the game play itself, rarely both. By turning the console off and on again I can switch between a good title screen and glitchy game play to a bad title screen and good game play. I'm testing on a Sony KV-PG14P10 CRT TV that normally doesn't have a problem with any composite signal I throw at it. My 32 inch LED TV doesn't seem to have the same problem but it has significant lag.

I'm stumped at this point. Maybe I just have a dud console? I think the previous owner must have lived next to the beach or something because there is a fair amount of corrosion on the motherboard. Maybe that has something to do with it.

I guess I'll just leave the RF unit in for CRTs and add S-video for modern TVs.
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Post Posted: Thu Apr 19, 2018 1:54 am
Is your console PAL or NTSC?

Either way hook up a SPDT switch to PIN 7 of the CXA1145. You will need to cut the trace to this pin first. Then connect this pin to the middle pin of the switch. Connect one outer switch pin to 5V and the other outer pin to gnd.

This will let you toggle the console between PAL/NTSC colour encoding. I've found some TV's play nicer with NTSC.
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Post Posted: Thu Apr 19, 2018 2:57 am
Frank_fjs wrote
Is your console PAL or NTSC?

Either way hook up a SPDT switch to PIN 7 of the CXA1145. You will need to cut the trace to this pin first. Then connect this pin to the middle pin of the switch. Connect one outer switch pin to 5V and the other outer pin to gnd.

This will let you toggle the console between PAL/NTSC colour encoding. I've found some TV's play nicer with NTSC.


It's PAL, I did the 50/60Hz mod and still getting the same results for both PAL & NTSC. Are there any issues with s-video mods? I think I will just skip composite if I cannot get it working 100%.
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Post Posted: Thu Apr 19, 2018 3:22 am
50/60Hz is not PAL/NTSC. It only changes the frequency and not the colour encoding. E.g. in 60Hz your console is outputting a PAL60 signal.

You need to do as I described in my post above re pin 7 to alter the colour encoding for a true PAL/NTSC signal.

I can't explain why my amp didn't work for you. Are you sure you connected it correctly? I ask as I've tested on at least half a dozen MS2 consoles, all that glitched with the standard AV mod and all were remedied with my amp.

S-video is fine and doesn't exhibit the same problem.
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Post Posted: Wed Apr 25, 2018 1:23 pm
So... I tried the circuit with the transistor in and whilst there is some slight improvement, I still have the flashing colour issue and a single diagonal line of what looks like interference rolling up the screen.

I've double checked grounding/accidental shorts and even tried "doubly" grounding it by grounding near the voltage regulator but it doesn't improve. I've also double checked the orientation of the caps and transistor.

Obviously this isn't a "finished article" but the image attached shows my attempt as I tested it. Can anyone spot anything obviously wrong?

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Post Posted: Thu Apr 26, 2018 1:47 am
Hard to follow but I don't think it's hooked up correctly.

I tend not to use the CXA to ground.

MasterGear sent me his console and I have it up and running smoothly with my amp.

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Post Posted: Thu Apr 26, 2018 6:10 am
As far as I’m aware I’ve followed the schematic. As I mentioned before I’ve tried different ground points and it hasn’t helped. Could you elaborate on what you think isn’t connected right?
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Post Posted: Thu Apr 26, 2018 11:24 pm
Try using shielded cable for the video signal and see if that helps. That should reduce stray noise getting into your video signal
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Post Posted: Thu Jun 21, 2018 5:18 am
wasup wrote
Try using shielded cable for the video signal and see if that helps. That should reduce stray noise getting into your video signal


I can confirm that the type of cable matters. After a lot of experimentation I was able to eliminate composite video glitches without the use of transistors to boost the signal.

I simply used an extremely thick wire, one I had taken from a PC power supply unit. I also made it as short as possible with the resistor and capacitor on the end. This has worked flawlessly for me. A really thick cable might seem like overkill but so far I have had zero screen jitters on a variety of games over several hours.

Possibly the same results can be achieved with shielded cable that is not as thick, but I haven't done any experiments with that yet.
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