Apple A1181 Repair

 The A1181 this machine I repair to three a 945 a 965, I heard there is a single bridge, but no repair to ado, disassemble it, hundreds of times. Ripped out the motherboard will. This motherboard K36A OEM number. The motherboard around the CPU above a lot of traces of corrosion of the influent. (I do not have a camera..) First test several large inductance of the main power, and did not see signs of a short circuit. It seems the problem is not large. The location clean water. So dry the power-on test. There is no standby voltage. DC first micro-power indicator light (normal in this board is not connected to the CMOS battery should be self-boot). Isolation protection circuit should not be working properly, open the drawing test. First find the   F6900

The test voltage of about 16V, no output level after the test D6901. Playing the output stage to resistance around 500, seems stage short-circuit. Measured the amount of D6901 pros and cons are infinite, open circuit, the find material board for a PPDCIN_G3H voltage out

Next test Q6950

123PIN the voltage normal 5678 but no output. Test the 4PIN voltage 9V about high level. The Q6950 is a P-channel MOS transistor 4PIN low conduction. Test Q6910 2PIN also low, Q6910 nonconductive, the Q6950 certainly high voltage. Q6910 controlled by U6950, U6950 controlled by U6900, test only about 1.5V U6900 2PIN normal should be 3.3. Playing on the ground resistance over 50. Remove the U6900 replies to more than 400. It seems U6900 shorted 

Then plug the power supply after the U6900 replacement can automatically power-on. But touch Northbridge temperature, CPU does ice. A test VCORE. The VCORE circuit with the ISL9504. Find this chip PDF to find online. Had to check into the drawing.

First test VIN 20PIN 0V, playing on the ground resistance over 60, had to first remove the chip.Test back to normal. Several important on-chip test chip pin. The 20PIN VIN 0V 22PIN VDD 5V 31PIN PVCC 5V 44PIN VRON 3.3V test to other places here too lazy tested. Pre-VIN. Voltage drawings defined PPVIN_S5_IMVP6_VIN. Before the class is R7120 10 ohms, the tests are normal. Test R7120 above 12V. The resistance back is 12V. I was depressed. Carefully looked pad. Original pin vias. Vias disconnected problem here,

The board vias Scratch fly line to the VIN pin. A good ISL9504 put everything is ready, plug adapter. Automatically boot, hand touch the CPU temperature rise is basically normal, and plug in the memory. Waveform oscilloscope hit SM_BUS. Clearly see the waveform of several transitions connected screen. The normal bright Machine, maintenance ends!