Symptom 1: Unit runs for a while then turns off
Symptom 2: Unit turns on, turns off immediately
This unit arrives after another tech had attempted repairs. Numerous screws missing from base and incorrect screws used in reassembly. Complete tear-down and disassembly.
After powering the unit up, I noticed that the heat sink copper was discolored [darkened] which is a sign of high heat. Upon close inspection I noticed a kink in the heatshrink material covering the wires for the fan wires, so I strip back a portion of the insulation and the red wire was broken, and the black wire was only 2 strands. Yellow and White wires were OK. Rather than replacing the fan (which is in short supply, and costly) I repaired the broken wires with solder and insulating them so that they would not short each other or the frame of the HS fan, which is negative ground.
Screw also missing on the exterior frame that holds the heatsink downward onto the base, this screw is important because it also keeps the heatsink pressed against the GPU allowing for the heat to be pulled away from the chip to be vented out from the unit. This unit was also upgraded to the modified custom copper shim to further assist in heat reduction.
Reason of varying symptoms:
This model may not require the fan to reply back to P.O.S.T. -so it would run, until it got too hot to continue. The ground (fans black wire) did not complete the circuit for the 'non-working' temp sensor to report that it was overheating. The CPU core thermal sensor eventually reported overheating before the fan could, or CPU thermal sensor would shut it down to protect the CPU. Then when the unit was immediately turn back on (while still over temp) it would shut off, since no correction was made, the info was reported to CMOS and would shut off.
This test should also be in your diagnostic 'toolkit' so that you also test the fans when you have an immediate shutdown, or runs & shutdown problems in this series [DV6000/9000/F700]. Also see the specs on MAX8734 power chip so you can identify this cause, since it do have a SHUTDOWN circuit [pin 6].
Cause: The screw had gone through the base and was smashing/pressing the wires again metal post, effecting shorting positive terminal of Fan lead coming from motherboard connector, and broken, no power reached the fan. The black wire [GND] was nearly broken so the fan circuit was not complete, as well as the speed (YEL) and temp sensor (WHI) circuit because there was no power reaching the fan.
The Max8734 is one of the major players in distributing voltages to sections of the motherboard.
MAX8734AEEI+ product name:
High-Efficiency, Quad-Output, Main Power-Supply Controllers for Notebook Computers