Galaxian - No Hit Sound

rchadd

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I have notice today that when Galaxip ship is hit there is no explosion sound.

I have found following information online regarding galaxian repairs:

http://www.arcades.plus.com/galaxianfix.htm

regarding sound generation it states:

"Fire

This is the noise made when you fire a missile at the galaxian horde. It is switched by the 74259 at 9L (pin 10). This charges the capacitor at C25, which in turn triggers the 4066 at 7R. To check to see if this is happening, use a logic probe at pin 11 of 7R, when you fire the signal should go high. Other chips to check are 7S and 7T. (7T being a common fault - this may also affect the hit and rack noise)

Hit

This is the explosion when your ship gets destroyed. Works in a similar way to the fire noise for triggering, coming from pin 7 of 9L, this time through C21 and onto pin 4 of the 4066 at 7R. Again, this can be checked with a probe. "


I have checked the pin 4 at 7R and it is constently High all the time.

I have checked at pin 7 of 9L and it goes from L to H when the explosion should trigger.

I see there is a resistor, diode D1 and capacitor C21 between the 9L and 7R.

I tested at one end of D1 and see it does L to H on Hit, but when i test at the other end of D1 (capacitor side) it is constently High. Is this expected?

Could this indicate a problem with the C21 or D1?

What other reason would keep pin 4 at 7R consently High?

Anyone understand the purpose of the capacitor and diode in the circuit? sorry i am not electronics expert! :)
 
well it seems i am now getting the Low to High transition occuring at pin 4 of 7R now when Galaxip is hit but there is still no explosion sound heard.

I would appreciate any advice on what else to look at?

All the other sounds seem to be playing successfully

thanks
 
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