Sega Model 2 A-CRX Dead or Alive garbage screen

skylab

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Hi guys, I've a sega model 2A board whit Dead or Alive game, when I power it I get a garbage for video, no sound. Only led 11 lights up in the cpu board. In the video board all four leds light up for about 1 second when I power up the board, then turn off.
Power supply voltage is 5v.
I've checked all connections, all pins of rom chips, everything seems ok.
The garbage is a bit different every time I power up the board. Test button and service button don't work.
 

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I don't think is a rom problem. If you search "sega model 2 broken" on ebay.com you can see some broken board with the same garbage and those are tested with working rom board.
 
My Dead or Alive pcb was doing that too. I have just the pcb and filterboard without the cage. My problem was the filterboard wasn't seated properly onto the pcb. It's working fine now.
 
All connections are ok. I see the same garbage without security board and/or without rom board. I think the problem aren't in security and rom boards. What have I to see in a working board without security board and/or without rom board? Black screen? Error message? Other?
 
Most likely its something on CPU Bd. CPU bd is dead. Garbage on any Model 2 or 2A aside from VC2 means hardware failure related to CPU Bd. Could be main program or something on Video Bd touching main address or datalines on CPU bd but I will say its something on CPU Bd. Could be corrosion, dead clock, bad buffers or RAM, opens on CPU or CPU controller.
 
Is it reparable? I've checked the oscillators with an oscilloscope and are ok, but I can't find clock signal in the i960 cpu. In according with the intel datasheet, pin 117 is clock signal, but I read a constant high level (about 5V). This pin si connected to a 74F245N but there isn't signal in any pins of this chip and there isn't signal in other nearby chips. Is it correct or is it a problem?
I've found 25MHz clock near 50MHz oscillator but not near intel i960 cpu.
 
Is it reparable? I've checked the oscillators with an oscilloscope and are ok, but I can't find clock signal in the i960 cpu. In according with the intel datasheet, pin 117 is clock signal, but I read a constant high level (about 5V). This pin si connected to a 74F245N but there isn't signal in any pins of this chip and there isn't signal in other nearby chips. Is it correct or is it a problem?
I've found 25MHz clock near 50MHz oscillator but not near intel i960 cpu.

Which datasheet are you referring to? The clock input is pin 91 (CLK2), not pin 117 (LAD15).
 
I've checked 91 pin and there is 50MHz clock (is it divided internally?). There aren't activity in any other pins. Failure pin is low. There aren't activity in program eproms (epr-19310 and epr-19311) but there are activity in others eprom like sound eproms.
There isn't corrosion or visible damage.
i960 cpu and security board warm in a few seconds (not hot). What can I check or do?
 
There are some news.
I dumped the i960 roms, the labels are epr-19310 and epr-19311, but in the mame source are epr-19310a and epr-19311a (with A). The label of rom board is "834-11342 B" but in the mame source is "834-11342" (wihtout B).
These roms are different:
epr-19310 CRC(3c571e75)
epr-19311 CRC(8818363d)
I tried these dump with mame but crash with this error: fatal error: i960: 634: unhandled ff.
Others roms I dumped are equals to the mame version.
Now I don't know if I have a broken board with good roms but different from mame version, or if I have a good board with broken roms (or broken board and broken roms).
I don't have a blank eproms and not even an uv eraser to check the board with roms of the mame version.
Could someone check my dump?
Thanks
 
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