Build Your Own Arcade Controls Forum

Main => Monitor/Video Forum => Topic started by: AE35 on July 19, 2008, 02:19:06 pm

Title: Jamma to RGB scart, do I need 220uF caps?
Post by: AE35 on July 19, 2008, 02:19:06 pm

Hey all!

I have a Sega STV in my cabinet with a 22" TV, and I'm using RGBS scart. It's been
perfect on all other PCB's, but with the STV the image is blooming..Everything in the high IRE's is washed out.

Right now the leads are just running directly from the Jamma til the scart, but I'm
thinking if I should put 220uF's on the RGB? (and what do they do anyway:))

Thanks!

Nicholas

Title: Re: Jamma to RGB scart, do I need 220uF caps?
Post by: Zebidee on July 27, 2008, 02:46:04 am

Arcade PCBs usually output the signals at a higher voltage.  Try using 75 ohm resistors on the RGB lines, but leave the sync alone.

Title: Re: Jamma to RGB scart, do I need 220uF caps?
Post by: MonMotha on July 27, 2008, 10:05:09 pm

SCART specifies that there can be a DC bias on the RGB lines, so it should already have any AC coupling needed.  Your monitor is probably expecting 0.7-1Vpp signals into 75 ohms from 75 ohms, but the arcade PCB is Hi-Z output (as they usually are). Put a 75 ohm resistor in series on the RGB video lines (not needed or desirable on sync) to form the proper back termination (like a SCART source would have) for ~2-3V signals commonly seen on arcade PCBs.  Increase this resistor if it is still blooming.