Bondi Blue iMac display issue (probable dying flyback transformer)

[StarkRG]

I recently got ahold of a Revision A Bondi Blue iMac and was ecstatic to discover that it was still operational. That is until I got the system software installed again and started using it. Every so often I'd hear a fairly loud "crack" usually accompanied by the image on the screen jumping or distorting and, occasionally, it would even shut off and come back on a second later and make a "degaussing" sound ("bummvvvv"). I figured that this would be a problem I'd need to address at some point soon but in less than an hour those occasional "cracks" turned into a constant loud buzzing (as if something was arcing, but without any kind of smell or smoke that I would associate with this). I figured it was probably a capacitor issue but, after disassembling the machine and removing both the power supply and analog boards, there is no obvious sign of bad capacitors (none sticking out at odd angles, no visible leakage, and no bulging). I know that's not conclusive at all, but, given how many capacitors there are in this thing I'd rather not have to replace all of them if it's not necessary (which it probably shouldn't be). After doing some research to see if there was any capacitors that are known to go bad I discovered that, actually, in these it's more often the flyback transformer that went bad. The symptoms don't line up with what's reported for a flyback transformer (it turns on, runs fine, the screen never died completely), but I think it's likely that what I have is just the very early symptoms that many people wouldn't have caught in time.

As I understand it flyback transformers aren't identical, even within the same product line, therefore I'd need to get the exact same one. The part number on my FBT is 6174z-1003g which seems to be very hard to find, however, there are a couple of 6174Z-2001G and a 6174Z-1003D FBT on ebay, and I wonder if anyone knows if one of these are close enough to work.

 

[Dog Cow]

I have a bondi iMac with the same symptoms, but I haven't done anything about it. Of course it's the flyback at fault, and not anything else. Energy that should go to the electron gun is instead being used to create the arc with its accompanying light and sound, which is why the display is momentarily affected.

 

[LaPorta]

Are they known to be very bad? My Bondi has been boxed up for the better part of 15 years or so...I remember we stopped using it because of an issue where the display would not power up upon startup. With hindsight, I think it was actually a bad PRAM battery, but I still haven't looked into it.

 

[StarkRG]

Yeah, it's a known problem with the first revision. Later models had issues with their power supply boards, but the earliest model's problem was the FBT. The battery in mine was completely dead so I took it out and ordered a new one, it still starts up, though (at least until the FBT goes completely. It's possible to run them with an external monitor since the internal display connects to the logic board with a standard Macintosh display port (which is compatible with VGA with an adapter) and, from what I've read, machines that don't start up due to this issue will start up if the internal display is disconnected.