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EDIT:
Everyone, please go to this thread instead, as it contains way more discussion:

https://www.smspower.org/forums/18045-JailbarsFixFound

Hey everyone.

So... I've known about this for a while now, based on my own research I did into SMS2 hardware. For those who don't know, Master System 1 and 2 are BOTH notorious for noisy RGB output; the most common complaint is about "jailbar" noise, which are faint vertical lines across the screen.

Well, I've had videos and technical notes about this for a while now, but nobody was seeing them. Well, a good friend of mine took my technical notes and wrote a step-by-step guide, and then I tweaked/modified his guide to be more complete.
https://retrofreedom.com/jailbarsms/jailbar.pdf

This step-by-step guide is based on my original technical notes which you can find here:
https://retrofreedom.com/sms2.html

I don't need to repeat much info here because you can find it in the resources I've provided, but here's a basic summary:

* Cut Z80 clock output from VDP. Cut Z80 clock input pin, leaving a bit left to solder on. Hardwire correct oscillator there. Because VDP clock division circuitry is done too near to analog video circuitry within the VDP

* Cut subcarrier (community already knew about this, and it's simply mentioned in my guide)

* Put 10uF power filter capacitors on 5v pins of SMS2 VDP (VA3 SMS1 has same VDP).

* THS7374 bypass if Alex Kidd SMS2 or *any* SMS1; with inline RGB resistors and RGB pull-downs on bypass board adjusted to give proper 700mV "75ohm level" RGB output on DIN plug. Sonic1 SMS2 uses a much better video encoder (MB3514) versus CXA1145 and doesn't need a bypass

* OPTIONAL: re-route VRAM lines going into VDP. (re-routing RAM/VRAM data/address lines on older SMS1 has been hinted at by a few other modders: I've not yet studied SMS1 myself but the person whom I worked with on the PDF guide has written, in the guide, some info about VA3 SMS1 which actually uses the same VDP as SMS2 and is basically an SMS2 electrically, just with SMS1 case, and has.... some motorbike game built into it I think?

Anyways yeah enjoy. I spent several weeks studying SMS2 hardware before coming up with the main fix (the oscillator bypass for CPU clock).

My name is Leah Rowe, twitter @n4of7 - I do research on retro gaming hardware all the time! So keep an eye on my twitter :)[url][/url]

Untitled.jpg (15.55 KB)

Links de-mangled, quite inventive mangling there.

lol yeah. i was being overkill in subverting the link restriction thingy. totally reasonable that you'd block links from new members, or members with low post count (to protect against abuse).

thanks for de-mangling the links!

I'm not used to forums anymore. It's been... years since I posted to forums on regular basis. An associate of mine told me that I should share my SMS2 findings on this forum, then I remembered i already have an account ;)

so hey maxim could you um, once you've verified this info in the guide and happy with it, link this info in a more permanent place? you have a dedicated section on the website for mods right?

or is this something i can do myself?

The dev wiki is editable by everyone. We'd be happy to host a mirror, as links rot. I'm not sure where else you'd want to link it from?

See also https://www.smspower.org/forums/18045-JailbarsFixFound which I guess is related.

lol yeah the SLR guy in that other thread learned from me. good guy

The PDF guide has been updated. Those who did those mod previously must be made aware:

Cutting CPU pin 6 cuts the 3.58mhz clock going to cartridge slot pin 47. Most carts don't use it, but you should go back and solder a wire jumper between pin 6 (connected to your oscillator aswell) to cartridge slot pin 47 on the solder side of the board.

We have discovered that doing the oscillator bypass to Z80 pin 6 results in a slight timing discrepancy between CPU and VDP. This is because not all oscillators have the exact same frequency, even for a given specified rate. In practise, this just means that games will show random garbage sprites on random parts of the screen, but only for a split second or two. If you want fully accurate game execution, it is recommended instead to wire a clock divider that takes the VDP's clock input 10.7mhz and divides by 3 to create the CPU clock; this will ensure perfect sync between VDP and Z80. Clock divider can be constructed using a simple circuit consisting mostly of flip flops; look online for info on how to do it, there are many youtube videos!

The PDF guide has been updated to reflect this.

Author	Message
retroleah Joined: 11 Dec 2019 Posts: 32 Location: United Kingdom	HOWTO: Completely remove jailbars on SMS2 Posted: Mon Aug 17, 2020 7:09 pm Last edited by retroleah on Fri Aug 28, 2020 8:12 am; edited 1 time in total
	EDIT: Everyone, please go to this thread instead, as it contains way more discussion: https://www.smspower.org/forums/18045-JailbarsFixFound Hey everyone. So... I've known about this for a while now, based on my own research I did into SMS2 hardware. For those who don't know, Master System 1 and 2 are BOTH notorious for noisy RGB output; the most common complaint is about "jailbar" noise, which are faint vertical lines across the screen. Well, I've had videos and technical notes about this for a while now, but nobody was seeing them. Well, a good friend of mine took my technical notes and wrote a step-by-step guide, and then I tweaked/modified his guide to be more complete. https://retrofreedom.com/jailbarsms/jailbar.pdf This step-by-step guide is based on my original technical notes which you can find here: https://retrofreedom.com/sms2.html I don't need to repeat much info here because you can find it in the resources I've provided, but here's a basic summary: * Cut Z80 clock output from VDP. Cut Z80 clock input pin, leaving a bit left to solder on. Hardwire correct oscillator there. Because VDP clock division circuitry is done too near to analog video circuitry within the VDP * Cut subcarrier (community already knew about this, and it's simply mentioned in my guide) * Put 10uF power filter capacitors on 5v pins of SMS2 VDP (VA3 SMS1 has same VDP). * THS7374 bypass if Alex Kidd SMS2 or any SMS1; with inline RGB resistors and RGB pull-downs on bypass board adjusted to give proper 700mV "75ohm level" RGB output on DIN plug. Sonic1 SMS2 uses a much better video encoder (MB3514) versus CXA1145 and doesn't need a bypass * OPTIONAL: re-route VRAM lines going into VDP. (re-routing RAM/VRAM data/address lines on older SMS1 has been hinted at by a few other modders: I've not yet studied SMS1 myself but the person whom I worked with on the PDF guide has written, in the guide, some info about VA3 SMS1 which actually uses the same VDP as SMS2 and is basically an SMS2 electrically, just with SMS1 case, and has.... some motorbike game built into it I think? Anyways yeah enjoy. I spent several weeks studying SMS2 hardware before coming up with the main fix (the oscillator bypass for CPU clock). My name is Leah Rowe, twitter @n4of7 - I do research on retro gaming hardware all the time! So keep an eye on my twitter :)[url][/url] Untitled.jpg (15.55 KB)

Maxim Site Admin Joined: 19 Oct 1999 Posts: 14744 Location: London	Posted: Mon Aug 17, 2020 7:18 pm
	Links de-mangled, quite inventive mangling there.

retroleah Joined: 11 Dec 2019 Posts: 32 Location: United Kingdom	Posted: Mon Aug 17, 2020 7:22 pm
	lol yeah. i was being overkill in subverting the link restriction thingy. totally reasonable that you'd block links from new members, or members with low post count (to protect against abuse). thanks for de-mangling the links! I'm not used to forums anymore. It's been... years since I posted to forums on regular basis. An associate of mine told me that I should share my SMS2 findings on this forum, then I remembered i already have an account ;)

retroleah Joined: 11 Dec 2019 Posts: 32 Location: United Kingdom	Posted: Mon Aug 17, 2020 7:42 pm
	so hey maxim could you um, once you've verified this info in the guide and happy with it, link this info in a more permanent place? you have a dedicated section on the website for mods right? or is this something i can do myself?

Maxim Site Admin Joined: 19 Oct 1999 Posts: 14744 Location: London	Posted: Mon Aug 17, 2020 8:32 pm
	The dev wiki is editable by everyone. We'd be happy to host a mirror, as links rot. I'm not sure where else you'd want to link it from? See also https://www.smspower.org/forums/18045-JailbarsFixFound which I guess is related.

retroleah Joined: 11 Dec 2019 Posts: 32 Location: United Kingdom	Posted: Mon Aug 17, 2020 8:39 pm
	lol yeah the SLR guy in that other thread learned from me. good guy

retroleah Joined: 11 Dec 2019 Posts: 32 Location: United Kingdom	Posted: Fri Aug 21, 2020 8:45 pm
	The PDF guide has been updated. Those who did those mod previously must be made aware: Cutting CPU pin 6 cuts the 3.58mhz clock going to cartridge slot pin 47. Most carts don't use it, but you should go back and solder a wire jumper between pin 6 (connected to your oscillator aswell) to cartridge slot pin 47 on the solder side of the board. We have discovered that doing the oscillator bypass to Z80 pin 6 results in a slight timing discrepancy between CPU and VDP. This is because not all oscillators have the exact same frequency, even for a given specified rate. In practise, this just means that games will show random garbage sprites on random parts of the screen, but only for a split second or two. If you want fully accurate game execution, it is recommended instead to wire a clock divider that takes the VDP's clock input 10.7mhz and divides by 3 to create the CPU clock; this will ensure perfect sync between VDP and Z80. Clock divider can be constructed using a simple circuit consisting mostly of flip flops; look online for info on how to do it, there are many youtube videos! The PDF guide has been updated to reflect this.

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