nanao ms9 15Khz mode w/ J-PAC

[donkey]

First time poster, so i'm probably doing something wrong - and its likely already been answered before but for the life of me I just dont know the right search terms to hit on my issue as i'm new to this. So here it goes;

Bought a new astro city cab, with nanao ms9 - this is confirmed the main PCB is exactly like the many pictures online. Its set to 15kHz mode.

I have a J-PAC, which is connected to the jamma harness. sync OK and sync IN LEDs stay lit.

The PC I have groovyarcade installed, and I think i've installed to harddrive in standard arcade 15kHz mode, it boots to HDD easily.

Finally the PC has a displayport connector (no VGA), so I bought a displayport -> VGA dongle to connected to the J-PAC.

The nanao ms9 cycles through red, blue, green horizontal lines that shoot up and to the left, all on top of a black screen. I suspect (and hope) this is just a pot tuning issue, but before I go attacking them with screwdrivers I wanted some guidance - am i doing the right thing here?

I should note, that before my attempted MAME install with J-PAC the cabinet had a simple jamma pcb installed and I haven't touched any of the monitor pots.

Thanks donkey.

[buttersoft]

Does the DP-to-VGA dongle handle 15kHz? Is the Jpac set to only pass 15kHz? Might help for troubleshooting this.

How do you know the system is booting fine? Are you VM-ing in or something?

And *when* do the horizontal shooting lines appear? Each time you connect the j-pac to the monitor, each time you connect the dongle to the J-pac, or only each time you power on the PC? Can you please post a picture of the lines you're talking about?

EDIT: any chance you're using this particular DP-to-VGA dongle? https://www.amazon.es/gp/product/B00Z08TZNU/

[donkey]

So, after picking this back up, and trying GM2020 edition, I've switched computers to a native VGA (HD-15) and not DP.

Lets recap, first time nanao ms9 15Khz w/ J-PAC (previously i think its been configured for ROM boards).

I know this is a noob question, but what do I have to adjust to get this screen stable? (and is it safe to adjust inside the nanao?)

[donkey]

ok update. the dual screen width is something J-PAC does to handle 31kHz being sent to it from the PC and then passing it as double width 15kHz to the nanao ms9 to protect it. Anyway, net-net its expected. So i've set the J-PAC jumper to only operate in 15kHz mode via only using the 15kHz jumper.

and i get what looks to be a h.hold issue. The nanao ms9 is set to 15kHz (as opposed to 24kHz) so I feel like i need to have a go at h.h.15 pot on the mainboard.

now not knowing whats safe and isnt safe when this CRT is powered on, I dont want to go fiddling in areas i shouldn't, esp with a screwdriver.

So how do people adjust the pots on the mainboard when the unit is on?

[buttersoft]

Two images side-by-side is 31kHz being fed into a 15kHz monitor. (Or in this case a multisync 15/31kHz set to 15kHz only?) The Jpac has the ability to cut out every second sync pulse here, but most old 15kHz CRT TV's will try to sync but only capture every second pulse, leading to the same image. Note that it's a bad idea to do that last with Arcade monitors the older they get, but the Jpac will protect you in the example of that pic. I'm not sure about the settings for that though, but you seem to be aware of that part.

Changing the Jpac to pass 15kHz-only won't alter the sync frequency of the input, so in your pic the GA PC must be outputting 31kHz. Which can't get past the Jpac now you changed it (but the rest of the video information can) and without horizontal sync the picture is scrambled. You didn't post another pic, so i guess that's what's going on.

For GA support, and how to get 15kHz, you'd be better off in the GroovyMAME subforum. I know next to nothing about that part