Is this a ceramic cap or a varistor?

[fabiodl]

Is this a ceramic cap or a varistor? I have only the pic so I cannot measure.

[inse]

I guess it's a 390pF ceramic cap.

[Ian.M]

Trace separations and widths look inadequate for mains power, so the odds of it being a varistor are pretty low before you even consider the markings.

[fabiodl]

Yep, it's on a 5V rail so I was 90% confident it's a cap, but even that it makes little sense.It's on the output of a LS04 on a totally logic circuit. I guess they wanted to slow down the edge.

[Kleinstein]

390 pF make a lot more sense than a 390 V varistor.  Sometimes LS logic was also used for some more analog functions. Some delay of noise filtering is possible, but also just an oscillator.

[Ian.M]

Yep, it's on a 5V rail so I was 90% confident it's a cap, but even that it makes little sense.It's on the output of a LS04 on a totally logic circuit. I guess they wanted to slow down the edge.

It looks like that sort of bodgery.  I'd bet there's a nasty asynch race condition somewhere upstream of it.  Typical 'design' process is late one Friday evening, with the deadline vanishing in the rear-view mirror:

Tech: "Eureka! It actually works now if I probe it here with a x1 scope probe!" 

Engineer: "Oh S--t!, we've got a glitch.   Its probably a race condition, but I'll need a couple of days to track it down and fix it.  May need a board re-spin." 

Boss:  "Hell NO!  The customer is already screaming, so its got to be done tonight. Redesign denied." 

Engineer:  Try bodging in a 39pF cap.  If it fixes it, we'll go up an order of magnitude so it *STAYS* fixed." 

[Gyro]

That's been used as an alternative to shipping with a scope probe attached many times!