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View topic - SMS 2 - AV MOD - sound works, no video?

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  • Joined: 19 Nov 2020
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SMS 2 - AV MOD - sound works, no video?
Post Posted: Thu Nov 19, 2020 4:58 pm
Hi Folks,

I stumbled across this forum while trying to diagnose my issues with an SMS 2 (UK/PAL 50hz)

I have done an AV mod (composite, pin 20) the sound works fine there is no video output.

RF works fine.

I have put the 3 RCA jacks in the case, taken ground from pin 1 on the CXA1145P and put across all 3 grounds, continuity tested etc no issues

Sound is from pin 9, to both L+R audio for pseudo stereo, the output is fine I hear alex kid demo from the speakers.

I have put a 75ohm resister on pin 20, wire from the resistor to a 220uf 10v capacitor positive leg, then soldered the negative leg to the RCA jack used for video.

I have tested it on a dell monitor that has composite in, nothing, a zx spectrum I modded for composite works fine, same cable.

I tested it on a TV also, an old first-gen none HD flat screen, nothing.

I am seeing 2.5v on pin 20 itself, 2.2v on the positive leg of the capacitor, 0 on the positive of the composite out RCA while I see 2.5V on the positive pins on the audio RCA jacks.

Any advice, I am going to swap the composite rca jack just incase its that causing it but I would appreciate any advice or questions.

Many Thanks.

Ant.
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Post Posted: Thu Nov 19, 2020 6:51 pm
My modded MS2 works fine without capacitor in video signal, only with 75 ohms resistor, maybe you can try it

I got audio form R19 and R20 resistor, check this external link. It is in spanish but you can see photos, and translate it to your language

https://www.briconsola.com/potenciar-consolas/master-system/
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Post Posted: Thu Nov 19, 2020 7:50 pm
I will give removing the capacitor a try now, the sound is fine though.
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Post Posted: Thu Nov 19, 2020 7:57 pm
Same without the capacitor.
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Post Posted: Thu Nov 19, 2020 9:11 pm
Try only Video signal, without audio.

Take ground from chasis

Try connect Ground to pin 18, if no works to 21, and rest grounds signals

It may work
scart_pinout.png (27.98 KB)
scart_pinout.png

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Post Posted: Thu Nov 19, 2020 9:43 pm
Tried removing the audio altogether, still no video.

Tried regrounding to chassis, still no video

Tried 18 and 21, still no video.

I am starting to think I am not getting any video output on pin 20, maybe a bad chip.

I have another few SMS II's on the way from eBay, I guess I will do the same with those.
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Post Posted: Thu Nov 19, 2020 10:29 pm
I've done loads of sms 2 machines as a composite mod, I no longer take video off the chip, but off the resistor next to it.

I will try and add a pic, I'd have to find my notes to see what I use, but its a resistor and capacitor then onto the video phono.

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Post Posted: Fri Nov 20, 2020 9:33 am
Thanks for taking the time to take a picture.

I just tried that, no difference.

I am wondering if the fact that I see no voltage on the positive pin on the video rca is something to do with it, I see 2.5v on the positive leg of the capacitor
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Post Posted: Fri Nov 20, 2020 9:47 am
I have just swapped the resistor, the capacitor and even the rca jack, absolutely no video signal, I hear the music though.

I think it is time to assume it is the chip.
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Post Posted: Fri Nov 20, 2020 9:55 am
But your rf works ok?
In theory that's probably just converting the same video from the chip I would have thought.
Can you get a closepic of your chip? Just to make sure its not shorting over 2 legs or something.
I did a similar thing before I realised the resistor held a video signal and was easier to solder to.

What size capacitor and resistor are you using and if you bell out the earth on the board (go from the surround on the edges) to the earth on the phono does it give a tone?

I will try and find my notes, they are on my work laptop somewhere lol
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Post Posted: Fri Nov 20, 2020 10:03 am
I have just made some progress, I took the capacitor and the resistor out of the equation, I got a picture, colours not great, some rubbish pixels on the bottom.

Added the capacitor back in (220uF 10v) and it still works, but still a pretty bad picture with lots of interference, I put the resistor back in, no picture at all again.

I suspect I may have some badly labelled resistors as 75k rather than 75r

I am going to have a hunt around for a different 75 ohm resistor and see if that was all the issue was all along.
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Post Posted: Fri Nov 20, 2020 10:12 am
Well thats a good sign at least then!


backtogeek wrote
I have just made some progress, I took the capacitor and the resistor out of the equation, I got a picture, colours not great, some rubbish pixels on the bottom.

Added the capacitor back in (220uF 10v) and it still works, but still a pretty bad picture with lots of interference, I put the resistor back in, no picture at all again.

I suspect I may have some badly labelled resistors as 75k rather than 75r

I am going to have a hunt around for a different 75 ohm resistor and see if that was all the issue was all along.
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Post Posted: Fri Nov 20, 2020 10:22 am
wow... lesson learned, do not rely on the labelling on the cheapest bulk resistor packs you buy from ebay/china.

I found another 75R pack, popped it in, perfect, a bit of noise still so I scratched up the ground plate surround on the board a bit and grounded to that, now it is working.

I am seeing the odd very minor glitch when running in 60hz mode which is not present in 50hz mode but its not gameplay affecting.

I did a very quick dirty solder job due to the number of steps I have gone through, I will redo a nice job that will help and hope that is that issue resolved :)

I really appreciate everyone's help and I hope this post helps someone else out someday!
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Post Posted: Fri Nov 20, 2020 10:24 am
Great News!
Glad you are up and running. :)

Now you can run it on 2 screens simultaneously, one with RF one with AV ;)
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Post Posted: Fri Nov 20, 2020 10:28 am
haha I guess you could yes... but why? haha

Tiny further update, the glitching only seems to impact the built in game and only in 60hz mode, I popped streets of rage cartridge in and it is fine.

Thanks again.

next step, full rgb mod, I have another MS 2 on its way to me.
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Post Posted: Fri Nov 20, 2020 10:43 am
backtogeek wrote
haha I guess you could yes... but why? haha


In my case I used it when I was doing an event to have a screen at either end of a table 😉

backtogeek wrote

next step, full rgb mod, I have another MS 2 on its way to me.


I'd be interested to know the solder points for that, I bought some din plugs ages ago, but never got round to looking or trying.
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Post Posted: Fri Nov 20, 2020 10:50 am
The pinout is on this page linked to earlier: https://www.briconsola.com/potenciar-consolas/master-system/ (scroll down)

I have finished resoldering it, made the wires as short as possible and I am pleased to say that all graphical glitches at 60hz have now gone also!



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Post Posted: Fri Nov 20, 2020 10:52 am
and excuse the extra hole, I did not judge well how close together they should go :(

There are no mistakes, only lessons!
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Post Posted: Fri Nov 20, 2020 11:50 am
Cool!

Interestingly, I don't take my audio from the top chip, I go from the same one you have your 50/60 mod switch.

The main reason for that is some ms2s have that tiny chip which was a nightmare to attach to. Lol
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Post Posted: Fri Nov 20, 2020 6:54 pm
Nice! You did it ;)
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