07 May 2023
The slot loading iMac G3s are convection cooled and have no internal fans for cooling. Over time the PAV (Power, Analogue, Video) board gets baked which can cause a multitude of problems. Tray loading iMacs have one fan but most of the heat dissipation is still reliant on convection.
If an iMac has had a productive and well used life it will now be in a much more delicate state. With the heat issues and aging of internal components, the following problems are known to occur.
Both iMac G3 models suffer from flyback transformer failure due to heat stress. The flyback transformer is located on the analogue board (PAV), and amplifies the voltage necessary for the CRT monitor to function. Both iMac models have insufficient ventilation/cooling of the analogue board. A flyback transformer has tightly wound wires which short when the insulation breaks down due to overheating. This results in the flyback transformer failing and causing the following behaviour:
It has become incredibly difficult to purchase new old stock flyback transformers (especially for the slot loaders). These flyback transformers are no longer produced, and the only available replacements are old stock or have been pulled from other iMacs.
WARNING: Replacing a flyback transformer is a specialist's job! The flyback and PAV board contain high voltage components which are capable of killing you even when the machine is completely powered off.
Slot Loading iMacs
All slot loading iMac G3s I have worked on have the LG CRT, and all have the same model flyback transformer. There may be different models used across the slot loaders so you should check your model before ordering a replacement.
The flyback model I have seen in slot loading iMacs is the Goldstar (LG) 6174Z-1017H.
In 2022 I was able to purchase an equivalent replacement (the HR Diemen HR46177 or HR 46177) from Dönberg Electronics. As of writing they no longer have any stock available. When I enquired to HR Diemen, and Efitier, their response was that they have no remaining stock and are no longer producing them.
As of writing Electronica USA have two HR46177 flyback transformers available.
Electronica Castro (Brazilian website) also seem to have some original models available - (I'm unsure on the validity of this website).
Tray Loading iMacs
I haven't worked on tray loading iMacs to confirm this but the flyback transformer model used in these machines should be 6174Z-1003G for the Revision1 board, and 6174Z-1017D for the Revison 2 board.
The MacOpz website has an excellent guide for Flyback transformer replacement in tray loading iMacs.