原帖由： ciradrak ,
fails Apple Hardware Test: 2I2C error
I have a 20" 1.8GHz iMac G5 from late 2004. It was having general instability problems so I tried putting a clean reinstall of the OS, but the process failed, three times in a row. So I ran the AHT disk which came with the machine, and it quickly failed the short test with the following error code: 2I2C/1/1:0x00000092 Sounds like it could be related to the I2C bus to me. However, the I2C system is mainly diagnostic and reporting in nature. It reports actual voltage levels on the ram cards and PCI slots, stuff like that. So possibly, this error may not be the real problem. I took the machine in to an Apple store and one of the techs noticed and showed me there was a bulging capacitor. Since they can only replace the whole board and send the old one back for remanufacturing (expensive), I wanted to try to fix it myself. After reading about the capacitor/power supply problems I got a new power supply and worked on identifying the capacitor and finding its specks. I learned that beyond the capacitive value, voltage, and temperature ratings; that there are three related charateristics which seem to be critical to the power filtering role these capacitors play in this machine. (impedance or Z)^2 = (equivalent resistance or ESR)^2 + (capacitive reactance or X)^2 If you know two of them you can compute the third. Typically ESR is small and Z ~= X. So why is this relevant? Well, the original capacitors are Chemi-Con KZJ Ultra Low impedance line with a Z = 12.5 m Ohms @ 100 kHz, unfortunately, this line was discontinued. Chemi-Con current offerings have impedances which range from 22 m Ohm to 49 m Ohm. Nowhere near the original spec. Worse, Digi-Key and Mouser don't carry the better lines, not even in a quantity of one! So I ordered the best available. When it arrived, I removed the bulging capacitor and soldered the new one into place. I also swapped out the power supply. Restarted the machine and... exactly the same problem as before. It still doesn't pass AHT, same error message. So, does anyone on here have some advice on what I should try next? Sorry about the long explanation, but hopefully it explains why I'm finding the whole thing puzzling. Why does Chemi-Con no longer manufacture capacitors with such low impedance any more? Why doesn't DigiKey carry what they do offer?
iMac G5 20" Model A1076