is a discolored Ceramic Capacitor bad?

[byoung]

I'm trying to diagnose a problem with an old Akai MPC60. I have yet to dive into it, but just on visual inspection I noticed that some(all but a couple actually) of the orange ceramic(possibly MICA) caps code 470J have turned grey near the leads.  It's just a semicircle area between the leads at the bottom of the caps.  I'm curious if these might be in need of replacement or if this is normal for older caps. Also there are a couple of cracked ceramic axial caps on the board(these look like resistors) and I'm assuming cracked=bad?

Here's a pic:

http://www.flickr.com/photos/39482223@N06/4195196897/?eOrig=4195191447


For those wondering I'm not a tech, and have only built a handful of units here on PP forums all of which work great!! So when this unit arrived with issues, I thought I'd take it to a reputable tech, VST pasadena, who pulled my RAM expansion and told me problem solved(clock noise randomly occuring in the outputs) and charged me almost what I paid for it.  I took it home and problem was still there, they didn't even pull any of the boards or check them, the screws were all still glued with original green glue.  After going back and forth with the head tech there, I got the response that these are old first gen machines and that they do strange things, have unavailable parts, and that I should live with it or move on, then he stopped responding to me.

So now I'm here trying to see if I can figure anything out on the analog end of it. DSP stuff....above my head.

 

[Svart]

discoloration could mean that something overheated.  This could be that the caps shorted out.  Pull one out and ohm it to see if it's shorted.  Ohm the circuit too to see if something is shorted.

 

[JohnRoberts]

I have never seen anything like that..

If it was shorted, you could test that without removing. If you have the ability to measure caps that size, pull one lead and measure it.

I would be curious if the discoloration looks like it's internal (from perhaps heating), or external some plating of contaminants or who knows what. I can't tell from the picture.

Or maybe it's nothing at all...

JR

 

[CJ]

solder vapor from the wave tank, move on, that ain't it.

when the board goes past the fluxer station, sometimes too many bubbles come up thru the holes and deposit on parts,

solder then finds the flux like silly putty on a newspaper. the Original silly putty, not the bootleg stuff from SingTao.

be sure it says "original" next time and you won't have life's problems.