Thank you for the JK operation info... armed with this valuable information i dived back into her. Chip in question is a 74ls161 NOT a 156 as i incorrectly stated earlier. I looked up the operation for this chip ( my problem was lack of output pin15 ).
The schematics for Zac games are very confusing.. you cant read them like you would a normal schematic. On the diagram, pin 1 input has a bubble on it indicating that input should be a LO... which i have so all is OK yes??

Not quite.... data operation states that Reset Input ( pin1) MUST be high for normal operation.... if its LO then ALL outputs are set to Lo.

 

You can see why working on these machines hurts your head.

So i check my IC.... input pin1 is LO.. all outputs including my pin15 are Lo.

Now the signal coming for this is from IC19, shown as a NOR gate..... looks like 2 highs in to a LO out.... WRONG... gotta read these daigrams as a logic gate schematic NOT what the signals are.

So i start to think that maybve i shouldnt worry about whats going in too much other than both signals should be the same.
RUN comes in as a LO... but i have a HIGH.. other input is a LO.... i go through RUN cct and start testing IC11 where it originates from...

Suddenly my CPU LED burst into life... IC11 is just off where my corrosion went to.. everything here looks good, but obvioulsy its not.

OK - CPU is now booting again.... not sure how long it will last as i must have a bad connection/ chip around IC11.
While the LED is lit i test the inputs to my 74LS161 and what do you know... have oscillation at pin15 as i should and input pin 1 should be HIGH!!!

RUN is now LO.

Bloody hell, its a bit rough when you cant trust a bubble   


I take my leads off the CPU ( im bench testing) and boot her again... seems she boots straight away with no first flash.

I plug her into the game and once again all solenoids are resetting. bang.. bang.. bang.

I disconnect POWER FAILURE wire from power supply and she still boots... this is wrong

I check power failure cct on CPU and i have the capacitor C5 discharging and charging... with each discharge the solenoids fire.. also each comma section on displays flash with each discharge... but these also strobe to each comma on whole display... no numbers are displayed.

So here i am..... back to 2 weeks ago or so... but i now know why the solenoids are firing at 2hz!