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What just happened to my recapped Classic II?


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Earlier today I had an urge to play the original SimCity and remembered that I had it installed on this Mac. So I turned it on, it binged, and the monitor started warming up, then I heard a loud *POP* and the monitor fizzed out for a little bit, then heard the bing again, indicating that the machine restarted. I turned it off immediately afterwards and unplugged it.

 
Now I can only assume this is a capacitor problem. But the odd thing is that I have had a lot of capacitors on this machine replaced very recently, including all the caps on the motherboard, and some of the caps on the analog board. I guess one of the unreplaced caps has gone bad.
 
I did a preliminary check on both the logic board and the analog board. I couldn't see anything wrong at all with the logic board when I took it out, but I don't think that's the source of the problem anyway. I took a flashlight to the analog board and looked around as best as I could without messing with the high-voltage stuff, but I couldn't see any blown caps or anything, and the fuse looks fine. There may have been something hiding that I couldn't see.
 
Could it also be something else, like the flyback transformer? Hope not.
Edited by ElementalChaos
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Was there a distinct smell after the pop? A fishy/skunky odour along with a loud pop would make me suspect line voltage filter capacitors. (the great big electrolytic capacitors generally near the AC inlet) If you smelled more of a burning or ozone smell, the flyback or other high voltage circuitry seems likely.

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Its probably the dreaded FBT judging by the pop and monitor fizzling... :(

 

You might as well (If its not the FBT) replace all of those caps before something else happens. Another thing is that if the FBT IS bad, it may have taken out a few capacitors if it exploded or something. Hopefully old ones. If sourcing a new FBT is easy, and you are up to replacing it, Id replace that and the other caps.

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Can you check voltages ?

 

I don't have a multimeter, but I think my buddy has one so I'll ask him for it. Where should I check and what voltages should I be looking for?

 

Was there a distinct smell after the pop? A fishy/skunky odour along with a loud pop would make me suspect line voltage filter capacitors. (the great big electrolytic capacitors generally near the AC inlet) If you smelled more of a burning or ozone smell, the flyback or other high voltage circuitry seems likely.

 

Yes. I forgot to mention it, but once I opened up the machine I was immediately hit with the smell of rotten fish. Which further leads me to believe that a capacitor has failed.

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I finally got around to taking everything apart, and found this:

 

IyMX6J9l.jpg

 

U1zr9oil.jpg

 

Those black pins are at the transformer... so that would indicate a failure there right? But the fishy smell as opposed to burning smell seems to go against that.

 

its probably the X1/X2 line safety caps that popped. These particular caps plastic shroud cracks with age, and allows moisture to seep in, shorting out the capacitor. 

 

Are you talking about the long reddish cap and blue cap here? That could be a definite candidate as the smell is strongest there.

 

I will probably replace both those as well as the two big filter caps. I've already found replacements for the other two online, but what should I replace the red one with?

 

UVt7K01l.jpg

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Looks like something got wedged between the plastic sheet and eventually slipped far enough to bridge the terminals. Part of the reason there's gaps between the traces is there's a high voltage present and the designers want to mitigate the chances of a trace-to-trace short, of course that means nothing when something bridges them. Whatever it was is now gone so you're safe to reassemble the machine and continue using it unless the short blew a winding in the transformer. Could of been a bug....could of been a piece of solder that came loose after a sloppy board reflow in the past. Don't worry about the caps. If they or anything else had failed you'd be seeing more then the scorch mark.

Edited by CelGen
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Hi,

 

just thinking, you may have a trouble with the Mosfet on QP2 (just below the blue capacitor) , this one goes bad from time to time, shorting a few things at the same time.

 

I you are lucky, will only blow the fuse.

 

Replacement should be IRFBC40.

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Looks like something got wedged between the plastic sheet and eventually slipped far enough to bridge the terminals. Part of the reason there's gaps between the traces is there's a high voltage present and the designers want to mitigate the chances of a trace-to-trace short, of course that means nothing when something bridges them. Whatever it was is now gone so you're safe to reassemble the machine and continue using it unless the short blew a winding in the transformer. Could of been a bug....could of been a piece of solder that came loose after a sloppy board reflow in the past. Don't worry about the caps. If they or anything else had failed you'd be seeing more then the scorch mark.

 

Are you sure? Fishy smell usually means capacitor failure.. I will still try and replace everything in that area just to be safe. (Other than the transformer, hopefully that's not damaged because there seems to be no replacement other than from another A.B.)

 

 

Hi,

 

just thinking, you may have a trouble with the Mosfet on QP2 (just below the blue capacitor) , this one goes bad from time to time, shorting a few things at the same time.

 

I you are lucky, will only blow the fuse.

 

Replacement should be IRFBC40.

That MOSFET did in fact fail in the past, I had it replaced at the same time most of the board was recapped. (Had someone else do it.) Is it possible it may have failed again due to the short?

 

If I end up replacing it, would I be able to use an IRFBC40APBF instead of IRFBC40? The former is a few bucks cheaper on Mouser and they have the same exact specs.

Edited by ElementalChaos
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I see nothing from your photograph that indicates a capacitor has failed either by leaking or blowing up. Seeing how the damage is only over two high voltage points I'm almost certain it's was because there was a foreign object inside.

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  • 2 weeks later...

what your describing sounds like what happened to me once, -I installed the incorrect capacitor ..it popped and I smelled that distinct fishy smell.  I replaced w/ the correct capacitor and all was well again.  I was able to find the blown capacitor but it wasn't that obvious ...the end cap was just slightly puffed, but not much.  

But it doesn't sound like your seeing anything w/ the capacitors ...good luck, these problems are always frustrating, but extremely rewarding once you solve.  :)

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