DC>> ok think of them as a 14 pin ttl dip ic, pin 1 is marked, then
 DC>> pin 14 is +5 and pin 7 is Gnd, the output is pin 8 from memory 
 DC>> and the
 DC>> output is 5v ttl levels.

 GM> Yeah, a continuity test on one of the boards showed the +5v and
 GM> ov rails. And I traced pin 8 to one of the other ICs. But I
 GM> wasn't sure of the fourth pin, whether that had some function or
 GM> not.

It's usually a no-connect. But there are a few that use it as an enable input, 
and some that use it as a voltage control input. Neither of those is very 
common, but they do exist.

Also, while 5V supply with TTL or HCMOS outputs are the most common, they're 
not universal. 3.3V oscillators are not unusual in newer equipment. 2.5V and 
1.8V are uncommon, but do exist. And there are other output types such as ECL 
and PECL. The sub 5V and unusual output varieties are more often found in 
surface mount packages, but they do occasionally appear in the common 4-lead 
dip14 and dip8 packages. There are even some canned oscillators with LVDS 
outputs. But those, of course, are never in the 4-lead dip packages.

Anyway, the majority of 4-lead dip oscillators you pull out of used computers 
are going to be 5V with TTL or HCMOS outputs and no-connect on pin1. Just be 
aware that there are exceptions.



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