BZ Tank Rumble sound intermident

Talon2000

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Got a BZ the other day.

It had no tank engine sound. After tracing through the circuit I found that it had a bad 555. Replaced and all is good. But in the middle of the game, no more engine sound.

Motor en are both high. and the 555 is sending clk. But I'm not getting anything out on pin 15 of the ls161.

I've done the normal things, egde con, interconnect, seated / cleaned pokeys, and arrays, and custom chips.

R11 has been checked, as I know this controls the frequency.

Ideas?
 
I've already replaced and checked f4, 5 the 74ls161, and have replaced e4 74ls04.

I've also replaced C29, and c11 coming off of the 555

Can anyone give me a better idea of what to look for.

Thanks
 
Got a chance to do some readings on the ls161's.. The clear sits at about .29vdc when the start button is hit, the clear goes high, to 4.99vdc. But no engine rumble. However when I pull the clear low (to ground) and release I have engine rumble.

Now my logic isn't as fresh on my mind as it was in college. But would the .29vdc cause this problem. Is not seeing the clear go high?
 
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