Mac Color Classic analog board crackles/whines/sizzles/hisses w/ video

[slaanesh]

I recently recapped the logic board on my Mac Color Classic (actually a Performa 250 but same thing)
The computer worked fine and readily switches on and everything seems to work.
The other day I started it again and I heard a strange noise from the rear.
So I opened it up and found that it was making strange noises - all the while working completely fine.
I recapped the power supply caps as recommended by recap-a-mac.
I also reflowed all the critical areas - I removed the older solder and add backed fresh solder and cleaned it up.
Of course, no difference. The board looks really fine, very clean.

Here's a video of the Mac Color Classic I took yesterday. Turn the sound up

Any suggestions?

 

[Callan]

Sounds like it might be your anode cap or flyback are leaking. It could be your anode cap isn't secured/seated properly. That or your flyback might have a crack. Put it in a dark room and see if you see any arcing. You recapped it so i'm not going to give you the whole spiel about monitor safety. Main thing is to make sure to ground the anode cap to the frame before you check.

 

[slaanesh]

Okay thanks for the reply. I did try taking a video in the dark but it was the middle of the day and it wasn’t that dark. I didn’t see any arcing. I’ve seen videos of this so I know what to look for. I’ll try again at night.
Anyway I could try sealing the top of the flyback with epoxy and see if that helps.

 

[slaanesh]

Here are some photos of the flyback when I removed it

 

[Callan]

Is this a crack in the casing?

 

[slaanesh]

Is this a crack in the casing?

Nah it's not. There is a bit of epoxy which seals the joins which happens to have blobbed out (from the factory).
I can't see any cracks or damage. In fact the flyback looks really good.
Anyway I had recently gone over some B&W flyback with some success so I just did the same to my CC and the crackle sound has diminished substantially. In fact with the case on and the cooling fan on I can't even hear it anymore.

 

[nottomhanks]

I had this EXACT SAME SOUND on my Color Classic analog board. Just a caveat, we had done the 640X480 VGA mod to optimize using a 575 Mystic upgrade. It was coming from the yellow transformer area. When the machine was making that noise, the screen would have lines on it and be kind of wavy. Try putting pressure on the black caps behind the yellow transformer or on the transformer itself. Obviously be careful with it being on. I found that when I put pressure on the transformer, that hissing noise would go away, and also the wavy lines on the screen. I wonder if there's a crack on the board that causes this. I have a video of it somewhere, but I'm fairly certain this is the same noises. Sometimes the machine would just violently SHUT DOWN while the hissing was happening.

 

[Arbee]

I found that when I put pressure on the transformer, that hissing noise would go away, and also the wavy lines on the screen. I wonder if there's a crack on the board that causes this. I have a video of it somewhere, but I'm fairly certain this is the same noises. Sometimes the machine would just violently SHUT DOWN while the hissing was happening.

That's likely cold/cracked solder joints on that transformer or a component near it. That was fairly common with the flyback transformer on the Apple IIgs RGB monitors. Touching them up would probably fix it.