--- On Sat, 11/12/11, Joe <[email protected]> wrote: <clip> > After it > sits powered off for several hours and is turned on again > the sound > returns. It happens when booted from the internal hard > drive or booted > from a floppy so it appears to be a hardware issue. > > Any ideas what it is or how to fix it?
Probably some filtering capacitors in the audio circuit need replaced. Pull the board out and closely examine the tops of all the capacitors, the small cylinders wrapped in plastic with a shiny metal end. The metal ends will have some lines pressed in, usually in an X or a K shape. Those are blowout vents. If something happens like a power surge those lines are supposed to be a weak point to rupture instead of the capacitor exploding and sending tiny conductive shrapnel into other circuitry. The problem is some capacitor manufacturers used an unstable formula for their capacitor electrolyte. (Google capacitor plague) Over time it decomposes and swells up. The tops of the capacitors bulge and eventually break. If the base plugs where the wires go in aren't good, the electrolyte can leak out there. If you find bulged capacitors they need replaced. Bottom leaking ones can be hard to spot if they've only leaked a little and didn't bulge the tops. Bottom leakers are worse because the electrolyte can be corrosive and damage traces on the circuit board. If you don't want to take a soldering iron to your Classic II's mainboard there are people who will do it for you. How much they charge for the service varies. Some will replace every capacitor known to fail, some take the tack that if a capacitor hasn't popped after so many years it's not going to, especially if others on the same board already have. That's what makes the electrolyte problem even worse, millions of the bad ones were made and got mixed into the supplies that almost every electronics manufacturer used for several years in the late 90's through early 00's. Some things got made with most or all bad caps, some things got only a few or even just one. I have a circa 2005 PC power supply with a single leaking capacitor, which I need to get replaced to make it good again. -- ----- You received this message because you are a member of the Vintage Macs group. The list FAQ is at http://lowendmac.com/lists/vintagemacs.shtml and our netiquette guide is at http://www.lowendmac.com/lists/netiquette.shtml To post to this group, send email to [email protected] To leave this group, send email to [email protected] For more options, visit this group at http://groups.google.com/group/vintage-macs Support for older Macs: http://lowendmac.com/services/
