Macintosh Plus fizzling on startup

[Apostrophe]

Hi all,

I know at some point I've seen some youtube video of a problem like this, so I thought I'd run this by you guys.

Last night I decided to turn on my Macintosh Plus. However, when I flipped the power switch, I heard the regular startup bong, but then a fizzling sound...like the sound something makes when you leave it too long in the stove. I half-expected smoke to come out; it was that kind of sound. But once the :?: icon appeared, however, the fizzling stopped, and the Plus worked just fine from there. At one point while playing around with floppy disks, I had to restart the computer by turning it off, then back on (not just the Restart command), and when I turned it back on there was no sign of the fizzling sound.

Is the sound just the CRT warming up in cold weather? Is this cause for concern?

-Apostrophe

 

[Gil]

That's sort of the case with my Performa 578. Except, the fizzling sound stops when you have an active window open on the desktop - if you don't, then the fizzling sound returns.

 

[Mac128]

Depends on the nature of the "fizzling" sound.

Could be a grounding problem. If the sound reoccurs, try opening it up and loosening and retightening the grounding plate screws and the grounding strap to the chassis.

It could also be Q3 on the analogue board failing. If this fails, it will take the flyback transformer with it. Is there ANY evidence of video problems, in particular an occasional "wiggling" along the right side of the screen? This would be an indication of something more serious heading your way ...

 

[Apostrophe]

No, I haven't seen any evidence of that. The screen's bright and clear; there was no wobble at all, as far as I could tell. If a deaf man were to start up the Plus, he would perceive nothing wrong.

I can certainly do what you said about re-tightening the grounding screw. I'll turn the Plus on again probably tomorrow, so then I'll be able to see if the fizzling persists and if so, take some action.

Very interesting, Gil...yeah, my problem is definitely similar to yours, in the sense that what's displayed determines the sound. When I first started up the Plus--you know how Pluses activate the CRT upon startup only briefly, then the screen shuts off and then comes back on with the icon? The fizzling sound was only there while the screen was doing its shut-off thing, but the moment it came back on, the fizzling disappeared.

But your problem seems to point to components on the boards rather than the actual CRT, since only the circuit board(s) determine what image the CRT actually displays. I might have a closer look at that analog board once I open the Plus up again.

I'll see if I can find that youtube video of this same problem...in rare cases, the people who post comments actually know what they're talking about, rather than the usual "ur computer's so old! lol" type of statements.

-Apostrophe

 

[shred]

If you turn the computer on with the back removed in a darkened room, can you see a blue electrical discharge ("corona discharge") around the top of the EHT transformer?

If so, the transformer really should be replaced, but you can get special high voltage silicone sealant and fix the insulation by liberally applying silicone goop to the top of the transformer. I can't remember the exact part number for the silicone, but it's for TV repair.

 

[Apostrophe]

I turned on the Plus again today. When I flipped the power switch, there was the startup bong and, I'm happy to say, no loud fizzling!

However, when I put my ear close to the machine's top vent right above the analog board, I did hear a clicking sound, as if the fizzle were more "spread out" this time. At that point I turned on my small fan that I focus on the machine's exterior to keep it cool, and several minutes later when I turned the small fan off so that I could hear the Plus, the clicking had stopped.

So my guess is that temperature definitely is a factor here. I had plugged it in only the previous night when it fizzled that first time, whereas this second time it had been plugged in longer, with that trickle of power keeping it at least a tiny bit warmer.

Just theories anyway...if anyone has had a similar problem feel free to pitch in and share your situation, ideas, etc.

-Apostrophe

 

[shred]

If its the insulation around the high voltage components breaking down, the problem will be related to humidity rather than temperature.

 

[H3NRY]

When a CRT is fired up after being off for a long time, there is often a sizzling or crackling sound sort of like it is taking a deep breath. It is caused by the inside of the tube charging up to high voltage, and this draws a charge through the coating on the outside to neutralize the voltage induced in the capacitor (coatings inside & outside the glass). Sometimes there is even a bit of sparking if the bare wire that grounds the outside isn't in good contact with the carbon paint. If the CRT has been used recently, it will retain enough charge that it doesn't make noise. You can see the charge on the front screen which will attract small bits of paper and dust.

If you're used to an LCD, this noise may seem strange, but they all do it.