Napco CCI-8DD intermittent problem

["DaveB" <dave@xxxxxxxxxxxxxxx>]

I have a ~ 20 year old Napco CCI-8DD alarm system in my home.
Recently, it's been having an intermittent problem every 2 weeks or so.

With the system on but not alarmed, the control panel(s) will start to
beep and flash the red, yellow & green lights in a random pattern for a
short while, then go back to normal.  The alarm never triggers (i.e.:
the siren doesn't sound).  During this time, the control panel won't
respond to any buttons.

I've checked the battery and the AC supply and both seem to be powering
the system.  I can see no loose wires.  I replaced the battery about 1
year ago.

Any suggestions as to what to look for or do next?

Thanks,
DaveB