JPAC Resolution issues

[MrMatt]

I'm using a JPAC with GM in 2 cabs.  One I set up over a year ago, and a new cab I've just finished.

I've noticed that the same issue is present in both installations which is making me think that I've done something wrong in both setups of my JPAC or CRT_emu.

Both cabs are Hatarex CRT monitors so I've kept the default 15kHz and 31kHz jumpers in the JPAC.

When both cabs boot, the PC BIOS POST screen just shows a scrambled screen like it is the wrong frequency.  I read that if the 31kHz jumper is present then it should display the screen doubled side by side because it's halved the 31kHz output, but I have never seen this in either cab.

When Windows gets to the login screen the video output syncs and the games appear to be running using superres etc, however if I remove the 31kHz jumper from either JPAC then when it boots into Windows and/or GM then the display is always scrambled like it's the wrong frequency still.

Have I done something wrong with my installation because when I try to use only 15kHz output with just that jumper inserted then my video output doesn't appear to be 15kHz.  It only works if I have both the 15kHz and 31kHz jumpers inserted, is this normal?

Whenever I'm in Windows or the MAME menu then the Windows resolution has always been glitchy and flickering, so maybe this is also a symptom that something is wrong with my video output?


My 2nd issue is I just bought a new cable to replace the stock VGA cable that comes with the JPAC but it doesn't appear to work.  Should this cable be OK?

https://www.amazon.co.uk/gp/product/B0799B4Q95

Thank you.

[MrMatt]

Anyone??

[DaddyLongLegs]

What video card are you using? If you don't have one, you should really consider one of the ATI cards that are supported by Atom15 and CRTemudriver.

No matter what I did with my JPAC, I always had a scrambled screen in the BIOS. Flashing Atom15 fixed it.

You can find it here: https://geedorah.com/eiusdemmodi/forum/viewtopic.php?id=64