Strange Defender setup problem

denikar

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Donor 4 years: 2012-2015
Joined
Jun 22, 2012
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Location
Canton, MI, Michigan
Have been working on debugging an early gen Defender CPU board and got it booting up with no errors. However when it goes into setup mode all I see for the parameters are question marks and it will not let me change anything.

Looking at the schematic the initial guess was the coin door write protection switch was the issue, but checking all the gates with a scope show everything to be in order. Also can't seem to manually put it in self test mode.

What else could be causing this issue? Bad CMOS RAM?

Thanks,

Tim
 
+1. Most likely the CMOS RAM. Make sure you socket that bad boy so you can fix it easier the next time.

ken
 
OK will try replacing. Thanks for the replies.

Was looking also at the RAMTRON option however the inputs to that are not directly compatible with TTL. According to the datasheet with VDD=5V the min allowed logic HIGH voltage Vihmin = 3.5V which is higher than the minimum level logic high TTL of 2.7V. One way to fix it is to put pullup resistors on every address and data line.
 
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