Sega Naomi board freezes/loops - Any thoughts?

krankcolc

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A couple days ago my Sega Naomi board froze up and ended up in a sound loop on MvC2 at my arcade. I shut it down, let it sit and powered it back up and it did the same after a couple matches. I switched over to Project Justice to see if it was the cart but got the same results. With PJ it took like an hour before it got to that point. I got a new Naomi mobo today, swapped it out and it worked perfectly all day today. Anyone know what would cause this freezing picture/looping sound?
 
First I would check all your votages at the PS. Then check your mother board to see if the fans are working and that its clean no dust all over the chips. That can cause overheating that leads to your issue.
 
most important part is to make sure that your +5 voltage is reading at 5.10V at the back of the main board, and that the 3.3V voltage is exactly 3.30V. if the 3.3V is too low or too high, it will cause your game to freeze.

the CPU fan to my understanding utilize hardware monitoring, as in, if they're not spinning or working properly, the board will go into a shut down mode (not to be confused with it freezing). maybe it's not that sophisticated, but I do know from experience that if it's unplugged, the board won't boot up. :)

start with the power supply. the power plugs on the back of the main board have red, yellow, white and brown wiring.

red = 12V (irrelevant, unless you lack sound, which isn't the problem)
yellow = +5V (check that this is 5.10, that's a safe operating voltage)
brown = 3.3V (check that this is 3.30 volts exactly, this will make your game freeze if it's out of adjustment)
white = ground

not entirely sure why Sega have to be dicks and use non-standard wiring colors.

if you have one of the original power supplies, there won't be knobs to adjust the voltages, you have to use a teeny tiny phillips screwdriver, and be very subtle with your adjusting and make sure you don't slip with it and hit something inside the unit that can get shorted out.
 
+1 on the power issue.

If the board is running at 5.2 or above you risk frying the very tiny 16 bit buffer chips on the board or cart. This will cause all kinds of hell, including random crashes or lockups.

Dirty fans or bad fans will cause things to overheat and die.

Also, the NAOMI 1 is prone to damage from a leaking supercap next to the battery. That electrolyte will eat traces and kill a NAOMI. Check for leaks and trace damage - especially under the 8 pin EEPROM next to it.

RJ
 
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