smiba
New member
[SOLVED]820-4668 - PP3V3_S4 low - If you power cycle the device ±50 times it will post
Alright, first time repairing an iMac here (What is the best way to do so on a bench by the way? I've tried to use my 5A bench power supply but the inrush on bootup is too high)
History of the device: The customer bought an external CD player over USB, but after plugging this in this drive the system powered off and wouldn't power on again.
After I thought I fixed the device I probed the USB ports, USB Port B is broken (It won't even power my USB Voltage detector) and Port A has a low voltage of 4.54V (Will power mouse and/or keyboard just fine). Port C&D are just at 5V as expected.
The second LED (LE0302) will glow brightly for ±200ms before going to a dim brightness, at that point PP3V3_S4 will be hanging around 1.3-1.7V or so.
I at first thought replacing U7600 would fix this issue and initially I thought that was the solution as after plugging in the device numerous times it suddenly worked and kept on working. Passed a full AHT test and kept on working for hours and being in suspend for half a day. I gave it back to the customer but sadly it died again a couple of hours later
When I took the device apart again I noticed the leds staying on a little bit longer on each try, so I started doing what I did last time, plugging the device in --> Waiting for the led(s) to go bright and then dim --> Unplug & repeat.
To my surprise after about 50 times (motivated by my curiosity) the device actually posted and chimed again! And is once again working now. But obviously this is not a long term solution and is in no way how I can return this device to the customer.
It goes like this:
0 times: LE0302 will flash really quickly and then glow dimly
10 times: LE0302 will be on for about ±0.5 seconds and the glow dimly
20 times: LE0302 will be on somewhere between 0.5 and 1 seconds before glowing dimply
30 times: LE0302 will be on for about 1 second, sometimes the 3rd led will power on as well for 1-2 seconds before going off and LE0302 glowing dimly
40 times: At this point the system might POST and chime or the 3rd led will be on for 3 seconds before LE0302 starts glowing dimly again
50 times: The system will now POST and chime and keep on working. Reboots and switching between sleep mode will work fine.
I have absolutely no idea what can be broken which will slowly restore its functionality? Any one any idea? Its confusing me quite badly. Only thing I can think about is that at some point a capacitor gets charged up far enough or something
When PP3V3_S4 stays hanging around 1.3-1.7V, PP3V3_S5 will not drop if I recall correctly. (But can't test since its working again now....)
Might U8400 be messing up? I don't remember if PM_EN_FET_P3V3_S4 stays high though, I think it did.
Cheers
Alright, first time repairing an iMac here (What is the best way to do so on a bench by the way? I've tried to use my 5A bench power supply but the inrush on bootup is too high)
History of the device: The customer bought an external CD player over USB, but after plugging this in this drive the system powered off and wouldn't power on again.
After I thought I fixed the device I probed the USB ports, USB Port B is broken (It won't even power my USB Voltage detector) and Port A has a low voltage of 4.54V (Will power mouse and/or keyboard just fine). Port C&D are just at 5V as expected.
The second LED (LE0302) will glow brightly for ±200ms before going to a dim brightness, at that point PP3V3_S4 will be hanging around 1.3-1.7V or so.
I at first thought replacing U7600 would fix this issue and initially I thought that was the solution as after plugging in the device numerous times it suddenly worked and kept on working. Passed a full AHT test and kept on working for hours and being in suspend for half a day. I gave it back to the customer but sadly it died again a couple of hours later
When I took the device apart again I noticed the leds staying on a little bit longer on each try, so I started doing what I did last time, plugging the device in --> Waiting for the led(s) to go bright and then dim --> Unplug & repeat.
To my surprise after about 50 times (motivated by my curiosity) the device actually posted and chimed again! And is once again working now. But obviously this is not a long term solution and is in no way how I can return this device to the customer.
It goes like this:
0 times: LE0302 will flash really quickly and then glow dimly
10 times: LE0302 will be on for about ±0.5 seconds and the glow dimly
20 times: LE0302 will be on somewhere between 0.5 and 1 seconds before glowing dimply
30 times: LE0302 will be on for about 1 second, sometimes the 3rd led will power on as well for 1-2 seconds before going off and LE0302 glowing dimly
40 times: At this point the system might POST and chime or the 3rd led will be on for 3 seconds before LE0302 starts glowing dimly again
50 times: The system will now POST and chime and keep on working. Reboots and switching between sleep mode will work fine.
I have absolutely no idea what can be broken which will slowly restore its functionality? Any one any idea? Its confusing me quite badly. Only thing I can think about is that at some point a capacitor gets charged up far enough or something
When PP3V3_S4 stays hanging around 1.3-1.7V, PP3V3_S5 will not drop if I recall correctly. (But can't test since its working again now....)
Might U8400 be messing up? I don't remember if PM_EN_FET_P3V3_S4 stays high though, I think it did.
Cheers
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