Centaur display sometimes doesn't work

robotype

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milano, Milano, Italy
sometimes I switch the game on and find all the displays are off, the ball in play display has some light in the lower part of the digits the other four are completely dark. I tested the voltages as described in pinrepair and all is good, adjusted all the connectors and nothing happens. removed cpu board and cleaned all sockets reflow headers etc. but I still get this problem, sometimes works fine, sometimes theya re black, sometimes ball in play display gives a dim-unstable 00-00 so I switch it on again and they don't work. then sometimes the suddenly reappear...I think it's an input problem because the voltage is there. any suggestion would be very appreciated.
 
If the voltages are present at the displays but all displays are working intermittently I would look at the blanking signal first. It will be common to all displays. Check it with a logic probe with the game in attract mode and the displays not working. If it's not strobing you've found the problem and you'll need to figure out why that signal is intermittent. Could be a socket, connector, etc...

If the blanking signal is strobing but the displays are still not working check the other signals with a logic probe and see what's not working. The display data, latches and enables should all be strobing during normal operation.
 
Something worth confirming as well - is the game fully booting (you're in attract mode, can start a game, etc.) when this occurs, or is the game dead?

Just want to clarify whether the game boots consistently - just sometimes the displays don't come up, vs. the game NOT booting intermittently, as evidenced by nothing on the displays.

If it's the latter, it's not a display-related issue and you need to find out what's keeping your MPU board from booting reliably. Check the number of flashes on the LED the next time it's doing this for starters.
 
The game always boots and works normal, only the displays are randomly dead...sometimes they shut off while playing and vice versa. the last time they did this I saw a 00-00 on the center display then they all went black. the strange thing is that jiggling connectors doesn't effect anything...it just decides when to light up the displays by itself so I am thinking some ic is failing. I have to probe blanking and other signals while the displays are not operating like Lindsey said, I'll be back.
 
now all the displays are permanently dead so I probed blanking pin 10 on all displays and it is stuck high so I followed the line and it went to the MPU IC U19 pin 4 and it's stuck high too so I replaced it and nothing changes. on my space invaders I get all three leds at U19 pin 4 but on the centaur it's red.
 
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