CRT Replacement

The flyback transformer is not a part by itself. And it is not a part of the CRT. It is a component soldered on the the analog video board. A repair shop that is experienced in CRT television repair may be able to desolder and replace the flyback transformer on the analog video board. The analog video board is one of two large boards mounted vertically along the side of the CRT (the other side has the power supply board). To get access to it, it is necessary to open up the iMac G3 beyond normal user access; it is somewhat complicated on the tray-loaders.

With the tray-loader iMac G3, there is a way to keep using the iMac by connecting the internal video connection to an external VGA display. When you do that, the internal video sub-system is bypassed, and it should pass the hardware self-test (and boot up). You can actually get up to 1600x1200 resolution, if the display supports it. But that would REALLY mess up the "original feel"; if you want more details about doing that, please post back.

I would be difficult to replace the internal CRT with an LCD. But it would be relatively easy to use an external VGA display, even an LCD display if it has the standard 4:3 aspect ratio (not widescreen) with VGA input. You can do this on the older tray-loaders, but not the newer slot-loaders.

On the tray-loader iMac G3, if you open the bottom panel, you will see two or three connections (the third one is for the IR sensor - not present on all tray-loaders). One of those connectors is the internal video connector. It is the one that looks like an old-style video connector with the two thumb screws. You can test to confirm the problem is on the analog video board by disconnecting that internal video cable and attempting to start up your iMac. You won't see anything in the display, but if it should sound like it starting up. Once it sounds like it got to the Desktop, you can press the power button and then Return to shut down.

However, that internal video port is not a VGA connector; it is an old-style Apple video port.

You need to get one of these adapters

[Apple Mac to VGA switchable video adapter TVCS-183|http://cgi.ebay.com/Apple-Mac-to-VGA-switchable-video-adapter-TVCS-183 W0QQitemZ360214053918QQcmdZViewItemQQptZLH_DefaultDomain_0?hash=item53de6e441e#h t_26404wt1161]

There are other similar ones, but I know this type works. Connect this type of adapter to the internal video port on the iMac. Then, you can connect a standard VGA cable and display to the adapter. The iMac should start up now, because you are bypassing the hardware failure on the analog video board. With the 333 MHz model, it has a whopping 6mb of VRAM and should be able to go as high as 1600x1200 at thousands of colors, or 1280x1024 at millions of colors (if the VGA display is large enough to handle it). The standard 1024x768 (and lower) will also work, of course.

If you find a repair shop that specializes in CRT TV repair, they could probably source the part. But they'd also have to be somewhat knowledgeable about repairing old Macs, which may be difficult. The difficult part would be knowing how to take it apart; once they do that, they could probably figure out what needs to be replaced.

There may be nothing wrong with your current CRT in the iMac. As I said previously, if the problem is the flyback transformer, that is a part that is on the analog video board, not the CRT itself. If you replaced the FBT on that board or replaced the entire board with one that was working, the CRT will probably work fine.

So that is a separate consideration from replacing the CRT with an LCD, which would be a difficult mod. LCD's are flat. The iMac display is curved. Therefore, the fix would not be good, even if the size was right. Also, the visible area of the iMac CRT screen is less than 15 inches diagonal (because CRT size is measured to the edge of the tube and not the visible area). An LCD that is 15-inch diagonal is actually 15-inch diagonal. So you would have to get one that was smaller, and that is pretty small; it would be a laptop LCD display.

Here is the repair procedure:
http://www.macopz.com/columns/imacrepair/

perhaps this will help...
http://arjoko.blogspot.com/200903_01archive.html

Robert