Asteroids test switch and circuit

I have an Asteroids board that, when switched between test and game mode
via the test switch, *won't* switch between the two unless you flip the
test switch (ie ground pin L) *then* press the reset button (a correctly
functioning board will switch as soon as the test switch is operated, ie
there should be no need to press the reset button).

 From looking at the schematics I see that the TEST signal is read by the
LS251 at L10 and the LS161 at C5, but these are changing states as they
should when edge connector pin L is grounded.

So what other part of the circuit would cause this problem? I could swear
that I've read about this somewhere in the dim and distant past, but I can
no longer find the reference.

As an aside, this board has a VSM fault - it will only play (blind) if pin
1 of the LS42 at L6 is cut ..... and we all know what a pain the VSM is to
diagnose.

Thanks,
Phil

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Received on Fri Nov 15 10:10:42 2002