Thunder cross 1 pcb strangeness

[slk486]

Hey guys, need your help.

Just received Thunder cross 1 in the mail. Board starts fine, graphics look fine and sound is fine.
When the game starts, however, the player ship explodes as soon as the invincibility flashing stops. The ship moves fine in that short period, but bullets from the ship look like they hit an invisible wall, ie. Sometimes they move across half the screen and sometimes only the muzzle flare is displayed.

I've reseated all eproms and made sure the two boards are connected properly.

+5v line on a arbitrary chip is 4.45. Is that enough?

Any ideas?

Edit: forgot to mention that demo mode exhibits same strange behavior.
Edit 2: Should also mention I'm using a Vogatek MK III supergun.

[rolins]

I had a similar problem on my Sky Shark pcb and the culprit was a bad rom chip.

You could also take out the eproms again, get some fine sand paper, and gently clean the pins until they're super shiny.
Also clean the jamma edge on the pcb with some rubbing alcohol & q-tips, then finish up with an eraser.

Have you tried adjusting the +5V on your power supply?

[slk486]

Looks like it is a voltage issue. I've changed PSU to one that delivers 4.65 on load and the issue is mostly gone, except when the screen gets really busy.

Don't have any better PSUs on hand, so may have to get a real Arcade PSU where I can tweak the +5v line.