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aarkay14

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Dear All,

I recently consolized a Neo Geo MVS 1C. I connected it to a 19 inch PVM but I get weird 'scanline losing power' kind of issue :( :(. I have used the 75Ohm termination and capacitor circuit as recommended to be used in RGB lines so I dont understand why is this happening :(

Please see the pictures below:
DSC_2158.jpg

DSC_2157.jpg

DSC_2159.jpg

DSC_2160.jpg


Video circuit is as below:
RGB_lines.png


Can someone assist me in finding the cause of this issue.

-Rama
 
That circuit is wrong for what you're trying to accomplish. Use a 220R resistor (or ~500R pot configured as variable resistor) in series on each R, G, B line and you'll be good. However, if you care about proper signal impedance, you may want to look into AV-DRIVER designed by viletim.
 
That circuit is wrong for what you're trying to accomplish. Use a 220R resistor (or ~500R pot configured as variable resistor) in series on each R, G, B line and you'll be good. However, if you care about proper signal impedance, you may want to look into AV-DRIVER designed by viletim.
So do you mean the below:

new_design.png


Also, Thank you for the link to Tim's device!
 
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Yes, that's exactly what RGB meant. Just wire a resistor in series between the RGB output and PVM input.

@RGB

Given this scenario of a fixed video output, is there an easier way to calculate and apply correct impedance?
 
Given this scenario of a fixed video output, is there an easier way to calculate and apply correct impedance?
In theory, yes, but you'll end up with wrong voltage level, so in practice this won't work as intended. Using just a 180-400R resistor in series will cause impedance mismatch, but at least you can get the signal to be electrically safe for the receiving equipment. Ideally, you want to use some kind of amp/buffer not only to provide the correct signal impedance for your TV, but also to minimize the PCB game amp's load (it's better for its longevity; it'a a high impedance amp designed for load to be 1K-10K).
 
@zeruel85 do you have more details on the board?
Which uses does it have or where might I be able to use it? Jamma 2 scart?
 
Thanks @zeruel85

Kind of need component values for it to be of any use. :)

Guessing you're using a 7374?
 
I designed a little PCB with the hints provided here by RGB some time ago, for my personal purposes, but now you can find the PCB on OSH Park, if someone is interested in it:

https://oshpark.com/shared_projects/CQtnJzfF

Hope it helps some of you guys. :)

Preview:
46073235fd9c14d51d5be03dd7c642c1.png
Hi Zeruel85!

Thank you for the link but please also let us know the BOM and Schematics of the same!

-Rama
 
So, this is the BOM for the RGBS4Jamma:
https://drive.google.com/open?id=1aIQ8REE21iiwGVad612jnoxLNyoRpupin9Lz-AMZDfA

As you can see, I didn't write the values for R11-R12, R21-R22, R31-R32, because those are the resistors for input voltage dividing.
You have to know how much attenuation you need for your purpose.

The law is:
V_red_out = V_red_in x R12 / (R11 + R12)
Of course same things for green and blue channels.

Just to make an example.
Imagine that we have 5V in input and want to attenuate the signal to 0.714V. If you use R11/R12/R31 = 3.65 kOhm and R12/R22/R32 = 620 Ohm, you will have V_out = 0.726V.
 
I picked the 7374, the remainder makes sense now with the additional info you provided. Thank you kindly.
 
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