Hello - wanted to introduce myself...
I've been a collector (on and off) of early 80's Arcade Games since late 1997.
I like just about anything and as of recent got back into trying to ressurect some old SEGA G80 - X/Y - stuff.
My current problem (and this is where I need some G80 expertiese), is that I have an X/Y - Control Card,
which as of recent, continues fails with the following ' faults ' :
(1.) Upon power up - screen shows random lines (drawn / blanked / drawn all over the place).
(2.) Connecting Output(s) to an O-Scope yields same problem / random lines being drawn.
(3.) Depressing the ' Test ' switch on CPU - Card - indicates - repated U27 Ram - Fault
(4.) Replacing every RAM (2114) chip - U21 -> U34 - has no effect / no change,
(5.) Removing RAM (2114) chips - has no effect - U27 Fault continues - as if Ram is not present.
(6.) Problem is isolated to the Control Card itself, (verified after Control card swap).
(7.) Problem seems to point to ' inability ' to either write to or perhaps access Ram by the CPU?
In an effort to try to resolve this issue, I have also gone in and replaced the following Parts(s)...
(please note: These were replaced one at a time - Board Powered after each instance - with no change).
(I have also added some notes - based on my limited knowledge of this particular ' Board ' )
U2 - Color Word is Read & Applied to RGB / DA - Converters (U5 and U1 - T) and associated Diodes/ Resistors.
U5 - Draw - Blank On / Off -
U3 - Compensates for Electron Beam - Deflection -
U10, U11, U12 - 74LS161 <- Vector Address Counter - Circuit - Loaded with First Address of the Line Instructions -
U14 - CPU DataBus <- D0 - D7
U15, U16, U17 - 74LS191 <- Vector Line Length Counters
U18 - Signal End - 74LS10 <-
U24 - U31 <- 2114 (RAM) -
U33 - Advances - 74LS283 <- Program Counter - by 10 counts - (if instructed Not to draw) -
U48 and U49 - 74LS244 <- Multiplexers - Allow CPU to Address Video Memory - U24 - U31
U50 - 74LS20 - Decoder <- Selects 1 of 15 outputs - goes >Low< & stores Video Words - in memory one at a time.
U51 - Sequences U50 <- through its 15 - count - cycle. At count 14 - Pin 16 of U50 - goes >Low< - to - DRAW.
U33, U34 and U22 Allow Character Words to be taken from Memory as the Program Counter Addresses
them via U36, U49, U35 and U21 -
Looking any information on how ' RAM ' on the G80 - Control Card is initially accessed (upon power up), by the CPU.
Appreciate any comments, suggestions or ideas that anyone may have.
Thanks,
-xxyyzz
I've been a collector (on and off) of early 80's Arcade Games since late 1997.
I like just about anything and as of recent got back into trying to ressurect some old SEGA G80 - X/Y - stuff.
My current problem (and this is where I need some G80 expertiese), is that I have an X/Y - Control Card,
which as of recent, continues fails with the following ' faults ' :
(1.) Upon power up - screen shows random lines (drawn / blanked / drawn all over the place).
(2.) Connecting Output(s) to an O-Scope yields same problem / random lines being drawn.
(3.) Depressing the ' Test ' switch on CPU - Card - indicates - repated U27 Ram - Fault
(4.) Replacing every RAM (2114) chip - U21 -> U34 - has no effect / no change,
(5.) Removing RAM (2114) chips - has no effect - U27 Fault continues - as if Ram is not present.
(6.) Problem is isolated to the Control Card itself, (verified after Control card swap).
(7.) Problem seems to point to ' inability ' to either write to or perhaps access Ram by the CPU?
In an effort to try to resolve this issue, I have also gone in and replaced the following Parts(s)...
(please note: These were replaced one at a time - Board Powered after each instance - with no change).
(I have also added some notes - based on my limited knowledge of this particular ' Board ' )
U2 - Color Word is Read & Applied to RGB / DA - Converters (U5 and U1 - T) and associated Diodes/ Resistors.
U5 - Draw - Blank On / Off -
U3 - Compensates for Electron Beam - Deflection -
U10, U11, U12 - 74LS161 <- Vector Address Counter - Circuit - Loaded with First Address of the Line Instructions -
U14 - CPU DataBus <- D0 - D7
U15, U16, U17 - 74LS191 <- Vector Line Length Counters
U18 - Signal End - 74LS10 <-
U24 - U31 <- 2114 (RAM) -
U33 - Advances - 74LS283 <- Program Counter - by 10 counts - (if instructed Not to draw) -
U48 and U49 - 74LS244 <- Multiplexers - Allow CPU to Address Video Memory - U24 - U31
U50 - 74LS20 - Decoder <- Selects 1 of 15 outputs - goes >Low< & stores Video Words - in memory one at a time.
U51 - Sequences U50 <- through its 15 - count - cycle. At count 14 - Pin 16 of U50 - goes >Low< - to - DRAW.
U33, U34 and U22 Allow Character Words to be taken from Memory as the Program Counter Addresses
them via U36, U49, U35 and U21 -
Looking any information on how ' RAM ' on the G80 - Control Card is initially accessed (upon power up), by the CPU.
Appreciate any comments, suggestions or ideas that anyone may have.
Thanks,
-xxyyzz
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