Re: 555 timer on Asteroids Deluxe

You're not using a CMOS 555, are you? You need a real old-fashioned 555
for this circuit (a CMOS one probably doesn't see the high level of the
12 KHz as going high enough).

Chris Loggans wrote:

>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 01:33:49 2003