Astro Wars Inputs - Solved

[vernimark]

something bad happened to my Astro Wars PCB.  
Inputs are not recognized but if I bypass the diodes on  switches, inputs work with a ghost key on "fire"button; in fact when I press "Fire" starhip fires and shifts on the left.  
Skip the diodes was just an experiment... I know it is an insane dehaviour  
I changed the 155 decoder that scan the input matrix but nothing changed. Signals are generated by this decoder and after the control panel go to the dedicated CPU passing through some pull-up resistors.
Checking by my scope signals on the CPU pins I can see the picture attached that, on my opinion, is not so good...
I ordered a new CPU so I'll update you once I can change it.

I never repaired a PCB based on input matrix, any suggestion?

vernimark

[PaulSwan]

Are you saying it worked and then stopped working or you are trying to wire it up?
Paul.

[vernimark]

it worked. it stopped working after the monitor had a HV "pop" on CRT HV "sucker". I don't know if events are effectively related but I can say for sure one month ago PCB worked.

[PaulSwan]

Are the diodes attached to the leaf the switches still good?
From your experiment bypassing the diodes, it sounds like the inputs are working but the matrix select outputs might not be working properly. I only have Quasar schematics in front of me, but they show the ROW select lines are driven by a couple of transistors on the outputs of a TTL chip (an LS04 on Quasar). I'd check if the transistors are working and being driven correctly by the TTL to start with.
Paul.
 

[vernimark]

I ll check similarities between quasar schematics and my pcb

[vernimark]

Hi, no significant similarities between two boards, but PCB now works.
Yesterday I substitute the HEF40097BP close to dip sw. So, restoration now is finished...