iMac G3 Possible Screen Issue?

[fyndr]

I have an iMac G3 revision B as part of my (very small) collection. Everything seems to be working great, but a couple of weeks back I noticed that every ten or twenty minutes or so after startup, the screen makes a small clicking sound and then flickers briefly (kind of like how the picture looks when degaussing a monitor, but not as dramatic) and returns to normal. There don't appear to be any adverse effects apart from the brief issue with the picture onscreen, but given its age I am a bit leery about the fact that this manifested relatively recently.

Could this be a problem with the analog board? As far as I'm aware no work has been done to the internals as far as caps or the CRT are concerned, so maybe it's a general indication that the machine is getting older and needs some revamping?

 

[Carboy7]

Huh, my one doesn't do that...

Then again, it's a Summer 2001 model... :-/

 

[jhorvath911]

flyback transformer; common issue.

 

[maceffects]

That is a much more common issue for slot loading models.  However, from what you describe I can say quite confidently that you have an issue with the analog board, most likely a failing capacitor or flyback transformer.  The CRT itself is fine.

 

[fyndr]

Thanks for the responses. I'll be looking at recapping all the boards in the G3 once I get my hands on an SE/30 (so I can send those boards out at the same time) and see if that helps alleviate the issue. In the meantime, is there a way to determine if the flyback transformer is at fault through visual inspection?

 

[techknight]

Work the screen and focus control back and forth over and over and then re-dial it back in, see if it still does it. 

 

[superpete]

Is that a diagnostic method Tech Knight, or a fix?

 

[fyndr]

Regarding the screen and focus control, are those dials that are internal to the machine? And also I assume the machine has to be on when I'm doing this since otherwise I wouldn't be able to see the results of the adjustments?

 

[techknight]

Is that a diagnostic method Tech Knight, or a fix?

Both. Potentiometers that are exposed to high voltage tend to collect dirt and they become noisy and love to drift. When they drift, your focus and screen brightness will drift with it.