RGB signal from MK4 board is very weak

[Hugo]

The RGB output from my Mortal Kombat 4 board seems very weak, resulting in a very dark screen.

The seller demonstrated that it worked (watched it run at his house) and the MK4 system test which automatically runs when turning the board on also seems to indicate the board is fine.

I tried to solve the problem by using a RGB signal increase board from Axunworks (https://www.axunworks.com/h-product-detail.html?goods_id=669521). This greatly increases the brightness, but the colors still look very pale. I also tested it on multiple TVs and scart cables, all with the same result.

Does anybody know how to solve this?

Also; does anybody know what mV the RGB lines should output? with 330 ohm resistors it's 275 mV and without around 400 mV. Wondering if the problem is with the board or my supergun/setup.

Please note; I turned the brightness way up on the photos, so it's not the more common strong RGB signal problem that can be fixed with 330 ohm resistors.

 

[stj]

is the video-ground pin on the jamma edge properly connected?

 

[Hugo]

is the video-ground pin on the jamma edge properly connected?

What's the best way to check this?

 

[stj]

to look at your adapter - does the pin actually connect to anything?

 

[digitron]

Do other pcb's look good on the same setup? You said you tried multiple scart cables, which ohm resistors are on your RGB lines on the scart cable(s)?

 

[Hugo]

to look at your adapter - does the pin actually connect to anything?

the jamma edge pins connect nice and tightly into the slot. Please note I tried it both on my supergun and RGB signal increase board with the same results.

Do other pcb's look good on the same setup? You said you tried multiple scart cables, which ohm resistors are on your RGB lines on the scart cable(s)?

This is my first and only PCB. The MK4 board came with 0 ohm resistors (which seems to be the default case) the issue occurred and I replaced them with 330 ohm resistors after tips from the community (which only made the image darker). I replaced the resistors on the board itself.

 

[digitron]

the jamma edge pins connect nice and tightly into the slot. Please note I tried it both on my supergun and RGB signal increase board with the same results.


This is my first and only PCB. The MK4 board came with 0 ohm resistors (which seems to be the default case) the issue occurred and I replaced them with 330 ohm resistors after tips from the community (which only made the image darker). I replaced the resistors on the board itself.

Grab your multimeter, set to Ohms, and check the RGB lines on your scart cable.

 

[jassin000]

This is a known issue with MK4 PCB, most people solve it by removing RGB resistors near the JAMMA edge.
Its not your cable/hardware.

Another very dim (but not as bad) PCB is the Irem M92.

*Disclaimer* I do NOT recommend modifying PCBs for stock/normal video issues, only stating I've seen this practice used in the past.

 

[Hugo]

This is a known issue with MK4 PCB, most people solve it by removing RGB resistors near the JAMMA edge.
Its not your cable/hardware.

Another very dim (but not as bad) PCB is the Irem M92.

*Disclaimer* I do NOT recommend modifying PCBs for stock/normal video issues, only stating I've seen this practice used in the past.

The common problem seems to be the RGB signal being too strong (very bright image). Which can be solved by replacing the 0 ohm resistors with 330 ohm resistors on the RGB lines.

I have the opposite problem; image is way too dark (tv brightness settings are on max in photos to at least see something). I don't think this can be solved by removing the resistors? since the default resistors are 0 ohm.