Changing an iMac's HVT

This tutorial is intended to be used by the unfortunate iMac CRT owners (especially the 1st generation iMac), facing a dead display problem. The usual symptoms requiring the replacement of the HVT are listed next :

The iMac seems to start, after the usual « Dong », the HD starts spinning and …. the computer switches off.

If you press the start button again, nothing happens, you have to wait a few minutes before you can reboot your computer.

Warnings :

This tutorial is not intended for Mac users who have installed Jaguar or Panther without the latest firmware update .

The described procedure is difficult to perform and potentially harmful if it is not carried out carefully.

When your iMac seems to show the symptoms described above, it is due to the analog video card. When the display should turn on, the computer suddenly switches off, as if there was a shot-circuit.

This phenomenon can be the result of many defective component found on this card (condensator, capacitance, etc…) but the weak point of the iMac CRT is the HVT (High Voltage Transformer). High voltage means danger, so be careful when performing the following operations.

A HVT can release 5000V shocks even when the computer is unplugged !! The HVT is responsible for most of the accidents linked to TV electrocution following opening of a TV or a monitor. So before doing anything, unplug power cable of your computer/monitor, press a few times the start/stop button, then wait at least a few hours to be sure that all condensators are empty.

When your iMac is facing a display problem, usually Apple Tech Support will offer you a standard exchange of the video card. This operation will cost you around 300 Euro. Due to the price of this type of 1st generation iMac, repairing via Apple Support is often as expensive as the computer itself….

The following technical tip, if you are skilled and follow the hereafter procedure, will cost you around 50 Euro, mostly the price of the HVT.

 

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