- Joined: 18 Mar 2018
- Posts: 7
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Master System II - No RF - Rough AV Mod Patchy
 Posted: Sat Feb 25, 2023 12:40 am
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Hi All,
New to the forum and opening up a Sega! Me and my son (8 years old) are well into our retro gaming, typically been into PS1 / PS2 / PSP and modding etc but recently we’ve been hunting in my parents loft and managed to dig out my original Megadrive and Master System II 😎😎
Megadrive still works spot on and we’ve been playing away but the master system unfortunately we can’t get a picture, we’ve an old CRT TV knocking about and can confirm it tunes fine to the Megadrive but nothing with the Master System II via RF.
Having recently had an appetite for modding and light repairs, installing a mod chip in the PS1, stripping down and repairing controllers etc we are keen to attempt to rescue the Master System as it’s in mint condition! Just to point out I’m far from an expert but a keen learner and we’ve been watching many YouTube videos / doing research on google etc and it’s nice my son has the interest which I had as a child.
Anyway rambling on a bit there - stripped the Master System down and we’ve tested all the obvious suggestions we watched on YouTube videos, regulator is getting 10v and outputs 5v (well 4.97v) when switch is powered up, we also have voltage on all the chips we are able to test (only have a standard multimeter - nothing flash) none of the chips get hot which could indicate a fault, none of the caps look blown, appreciate they could be but my multimeter doesn’t test for capacitance. Board and traces look OK and I gave some not so clever looking solder joints a reflow and cleaned the entire board with 99% isopropyl. Obviously we don’t have an oscilloscope so I can only test so far. TBH I’m limited into knowing what I’m doing with my multimeter.
Having got as far as I could I saw the AV mod so thought I’ve nothing to lose. Not having all the exact components to hand we tried this -
Took an old cheap rca cable and cut the plugs off one end, separated the ground wire and signal wire, ran a wire from pin 20 solder point on the rear of the board, to the lowest resistor I had which was 470 ohms and then to a 10v 470uf cap then onto the signal wire exposed from the cheap rca we cut the end off, ground wire from pin 1 to the rca ground wire.
This did give us a very very rough picture - no colour and flicking - but at least it was progress, we also tried it without the resistor and without the cap, but it didn’t really make any difference to the picture. (Added images to the bottom of the post)
Appreciate this was a very very rough attempt with the objective of seeing if we had video on pin 20. My questions would be -
By getting a 75ohm resistor and possibly thicker wiring as we used 30 AWG, and some proper rca female panel mounts - should we get colour and a better picture? As ours isn’t anywhere near playable.
I’m nervous that the problem is deeper as some videos I’ve seen of some people doing the AV mod get a clear, stable, colour picture with a pretty rough wiring setup and no resistor or cap.
Be glad of some advice!
Thanks in advance.
Simon
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- Joined: 14 Aug 2000
- Posts: 742
- Location: Adelaide, Australia
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Master System II - No RF - Rough AV Mod Patchy
Posted: Sun Feb 26, 2023 12:53 pm
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It looks like you've connected your cable to pin 21 of the CXA1145 instead of pin 20.
Pin 21 is the one of the RGB pins.
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- Joined: 18 Mar 2018
- Posts: 7
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Posted: Sun Feb 26, 2023 1:38 pm
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You know what, looking at that picture it does look like pin 21!
I will check shortly and report back!
What a basic error that could be!
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- Joined: 18 Mar 2018
- Posts: 7
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Posted: Sun Feb 26, 2023 9:33 pm
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asynchronous wrote It looks like you've connected your cable to pin 21 of the CXA1145 instead of pin 20.
Pin 21 is the one of the RGB pins.
Sir I owe you a beer 🍺
What a rookie mistake! Feel like a right tool! Crazy thing is I watched a video where someone went to that pin! I knew it was pin 20 I needed too 😳
All working good now! I get a few line bars keep flashing across the screen but it’s only hooked up rough and I’m using a 470ohm resistor and a 10v 470uf cap, so I need to order the right ones now (75ohm a resistor and a 10v 220uf cap) hence why the picture is dark too and I hope that my kill the flashing bars too.
Get some rca panels jacks ordered and keep my fingers crossed 🤞
(See the line bar in picture 2)
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