A decrease in insulation resistance leads to an increase in current leakage from one electrode to the other… …The third failure mode is a reduction of the insulation resistance, which is the parallel resistance of the capacitor. The presence of humidity in the capacitor, because of poor drying during the manufacturing process, or because the moisture permeability of the material was too high, or because the humidity level where the capacitors are installed was too high, may lead to three failure modes… These capacitors are energized and in use any time the computer is plugged into mains power, even if the computer itself is shutdown.Īside from the possibility of overvoltage, voltage transient events and age there is likely another cause for this capacitor failure: The capacitors we’re dealing with here are at least 36 years old, and likely with many years of active service. Because of this direct connection to the AC voltage, the capacitors may be subjected to overvoltages and/or voltage transients-lightning strikes, power surges.” 1 In order for these capacitors to perform their EMI/RFI filtering tasks, they are directly connected to the AC power input, that is, the AC “line” and the AC “neutral”. Their primary purpose is to “minimize the generation of Electromagnetic Interference and the negative effects associated with received radio-frequency interference. The surface mount capacitors that most often fail in vintage computers are film foil style, AC line filtering capacitors. #Mac plus computer case mac#You should hear the familiar startup chime, see a Happy Mac icon and a have a Macintosh computer with a new lease on life. Assuming all is well, proceed to power on the Macintosh. If you see, smell or hear something abnormal, quickly disconnect the power and investigate. Connect your Macintosh to mains power, look and listen for anything out of the ordinary. Once the case has been reinstalled, it’s now time to test. Interior view of a Macintosh Plus Smoke Testing Macintosh Plus Analog Board Front and Back You can now set the remainder of your Macintosh Plus aside, as you only need the analog board for the remainder of this project. You also need to remove the white protective cover from the back of the analog board. Once your CRT has been discharged and the anode cap removed from the back of the CRT, you’re now able to remove the analog board from the rest of the computer.Ĭarefully slide the analog board up and out of the case making sure all wires and connectors are completely free. IFixit has a terrific teardown guide which should provide the detail needed to successfully complete this disassembly. To access the analog board, which contains the circuitry for the power supply you need to disconnect the floppy disk cable, power supply cable, ground screw, neck board connector and the anode cap. Please familiarize yourself with the procedure to safely discharge your CRT’s anode cap before venturing further. This charge dissipates over time, however there is a very real possibility that your CRT still has a charge in it’s capacitors and therefor could provide a nasty shock. Hardware NeededĬRT monitors operate with extremely high voltage, 10kV - 15kV (10,000 - 15,000 Volts), which at a high enough amperage is absolutely fatal to humans. While this guide is specific to capacitor replacement for vintage Macintosh computers, the overall guidance, parts list and replacement techniques would remain the same. Many non-Apple IBM-compatible computers from the late 1970s through the 1980s also utilize the exact same RIFA capacitor, which fails in the exact same way. #Mac plus computer case Pc#Fortunately, this is a straightforward project requiring less than $3 in parts and simple through-hole soldering.Īlso, if you’ve just acquired a vintage PC or Macintosh, it’s a really good idea to replace this capacitor as a preventative measure before it fails. If you’ve ever been using a vintage computer and it started to spew noxious smelling smoke, this capacitor has just failed and must be replaced. If you have a vintage PC or Macintosh Computer, including the Apple //, Apple //e, Macintosh 128K, Macintosh 512K, Macintosh Plus, Macintosh SE or Macintosh SE/30, there’s a very high chance that you have a RIFA filtering capacitor installed in your power supply which is close to failure.
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