555 timer on Asteroids Deluxe

I have a problem with the -30v circuit for the EAROM
on an Asteroids Deluxe. When I first tested the board
with the original 555 in place, the output at pin 3
was a constant +15v. Since then, I have tried 2
different (new) 555's and have tried isolating the
output by disconnecting everything downstream, but I
still get a steady +15v when I would expect a 0-15v
square wave. The 555 only has a couple inputs (+15,
GND and 12 KHz sq. wave) and they are all correct. I
even compared all inputs to a known working board and
everything matched. What am I missing here? The only
thing I have yet to try is to pull a 555 off of a
working Ast Dlx board and install it on this board to
eliminate any problems with my replacement 555's. Any
suggestions as to why I am not seeing the square wave
on pin 3?

Thanks,
-Chris

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Received on Fri May 23 01:19:47 2003