JAMMA to SCART TV cum arcade monitor

[Zebidee]

Thought a few people might be interested in this.   

I just picked up two old cabs with complete JAMMA systems in them, and mounted my 27" Sony Professional Video Monitors (SCART input) into them.  As these Sony's are really nice, I really wanted to make these cabs into proper JAMMA cabs, capable of using a PCB or JPAC. 

I've converted some SCART TVs to arcade monitors by using a VGA-SCART cable, but what I really wanted to do was run the video input through a JAMMA connection. This sounds pretty straightforward until you realise that a JPAC amplifies the RGB signals to arcade monitor levels, which are too high.  It works, but the brightness is way too high and it probably damages components over time.  TVs expect a signal level of about 0.7v average, but an arcade monitor expects around twice that or more. 

Because normal arcade PCBs also amplify the video signal, this was a real problem.  I solved it simply by putting some small resistors (75ohm, 6 cents each) on each of the R, G & B signal lines in my JAMMA-SCART cable.  This reduced the signal voltages to more acceptable/normal levels for the SCART input, brought the brightness levels back into line and improved the clarity/contrast.  I still reduced the brightness control, but only very slightly.

I had two cabinets to do, so on the second one I put slightly stronger resistors (110 ohm, also 6c ea.) onto the RGB signal lines on my JAMMA-SCART cable.  This worked even better, and the picture required very little adjustment to be perfect.