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Hi,
Dropped A1586 here that had a short on PP3V0_NAND. faulty cap located and replaced.
Device now boots up with no image on the screen. PP6V0_LCM and PP_5V7 next to this are ok. There is backlight but I’m wondering because the PMIC did get very hot before the initial NAND short was removed, the adjacent Oscar gets hot now.
I’m wondering what would be the next thing to test/look for?
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The first thing to do is to properly probe (and compare to known-good) the Chestnut circuit as that is responsible for display and Touch. Also probe the LCD and Digitizer FPC connector against a known-good to see if other rails and signals are problematic.
Then I would start probing the main outputs from the PMIC to see if one of them is shorted. This can cause a cascade of effects as most circuits also use other power lines, especially the 1V8 line.
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Always appreciate your replies Minho! On this one I've Used ZXW and a known good board, all FPC values are normal in doide mode. Also around chestnut and
In diode mode I get 298 on the 1V8 line (for the bad board) but 328 on the good board, this to me doesn't seem like too bad a difference at all.
EDIT: I removed one cap that got hot only when booted. Freeze spray was used for this. one Device just went to recovery mode but I am seeing grey lines on screen, so some image is working ... continuing work on this one
I wouldn't be concerned about a 0.030 difference between the boards.
Phone updates fine from DFU mode and I see lines on the screen. once updated it does go black and back to DFU mode. I have replaced all CPU caps that looked bad or got the hottest with freeze spray. The PMIC is something that does still get hot but none of the voltages it gives out have come back with anything unusual. Really weird this one but it is still ongoing.
Thank you Minho for your comments!
One thing I will say is that I am now seeing PP5V1_Grape_VDDH is reading at zero, this connects both the chestnut IC and Cumulus I think., would it be best to look at the lines these two give off and investigate?
Zero what? Ohms, volts, diode mode?
Yes, you should investigate this further :>).
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