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| {{Repair Guide | | {{Repair Guide |
| |Device=MacBook Pro A2337 | | |Device=MacBook Pro A1708 |
| |Affects parts=display board, main board | | |Affects parts=Motherboard |
| |Needs equipment=multimeter, soldering iron, soldering station | | |Needs equipment=multimeter, soldering iron, soldering station, thermal camera |
| |Type=Soldering, Part replacement | | |Type=Soldering |
| |Difficulty=3. Hard | | |Difficulty=3. Hard |
| }} | | }} |
| {{stub}} | | {{stub}} |
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| ==Problem description== | | ==Problem description== |
| No backlight on display on the 820-02016 Logic Board, The laptop turns on, LCD is displaying a picture but without backlight. | | <nowiki>#</nowiki>incomplete |
| | | [[File:Placeholder image.jpg|thumb|Example image (Figure 1) -- No image yet. Help expand this page by uploading it!]] |
| ==Symptoms== | | ==Symptoms== |
| [[File:Placeholder image.jpg|thumb|Example image (Figure 1) -- No image yet. Help expand this page by uploading it!]]
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| Detail all measurable or observable symptoms in this section.
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| *No Backlight | | *sub 20 ohms on PPBUS_G3H |
| *All voltage rails are normal | | *Not turning on |
| *Possible liquid damage/corrosion
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| ==Solution== | | ==Solution== |
| ===Diagnostic Steps===
| | [[How to find short circuits]] |
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| ====Failed display TCON board or a failed display LED strip====
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| *Check for a short to ground on backlight output (PPVOUT_LCDBKLT)
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| **CP860 or adjacent capacitors in the series is an appropriate area to measure, since it does not require removal of the system board.
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| **If a short to ground is measured, unplug the display connector to rule out a potential short to ground within the TCON board or LED strip of the display.
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| ====Short to ground on backlight output caused by a failed output decoupling capacitor (Most common)====
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| *Check for a short on the backlight output while the screen is unplugged
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| **CP860 or adjacent capacitors in the series is an appropriate area to measure, since it does not require removal of the system board.
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| *If the short is persistent with the screen unplugged, proceed to the "Backlight output shorted to ground" repair steps below.
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| ====Failed backlight driver (UP800)====
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| *UP800 is in a prime spot to be hit with liquid on the ''820-02016'' and is very commonly seen to be corroded after history of liquid damage.
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| **Failure of UP800 without the presence of liquid damage is uncommon, however if you have no backlight with a known good display, and do not have a short on backlight output, UP800 may be bad or you may have another circuit fault such as a bad resistor or broken trace within the UP800/backlight generation circuit.
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| **If UP800 is corroded, replace it along with any other corroded resistors or capacitors adjacent to it.
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| *It is common for current sensing pins (pins 9 and 10) of UP800 to be very corroded with corresponding pad/trace damage.
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| **gently scrape the coating off of the traces going to pins 9 and 10 of UP800 and run jumper wires from the traces to pins 9 and 10 of UP800.
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| **0.02mm jumper wire is recommended.
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| *Ensure that the backlight circuit has its input voltage (VIN) by measuring on BOTH SIDES of FP800, which is the backlight fuse.
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| **Voltage on both sides of the fuse should be equivalent to PPBUS_AON.
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| **If the backlight fuse is blown, check for a short on backlight output (PPVOUT_LCDBKLT) and on backlight input (PPVIN_LCDBKLT_F).
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| **If the fuse is blown without a short, proceed to the "Backlight fuse (FP800) blown in the absence of a short to ground" repair steps below.
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| *Check that the backlight circuit is being enabled, the screen will need to be connected for the enable signal to be sent out.
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| **measure voltage on RP842. BKLT_EN_R / BL_PWR_EN should measure around 1.8v while a GOOD known display is connected.
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| ***If backlight EN is missing, be sure that you do not have a parts issue with your display or logic board to display cable.
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| ***BKLT_EN missing on this board due to a board issue is very rare, but may be cause by a failed PMIC (U8100) or failed iGPU in the M1 SoC itself.
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| *Ensure you have continuity between pin 1 of RP831 (LCDBKLT_FB_XWR) and PPVOUT_LCDBKLT.
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| **Although rare on this board, it is worth checking to see if the backlight feedback trace is blown. Without feedback, the backlight driver will not produce its output.
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| *Check the 5v input to UP800 (PP5v_BKLT_A and PP5v_BKLT_D).
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| **RP845 or RP844 may blow if UP800 fails. Ensure you have 5v on both of the above listed lines. If low, replace the blown resistor(s) and UP800.
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| *'''If you have VIN (PPVIN_LCDBKLT_F), Enable (BKLT_EN), and both 5v lines (PP5v_BKLT_A and PP5v_BKLT_D), and no backlight output with the absence of a short to ground, replace the backlight driver (UP800).'''
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| ===Repair Steps===
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| ====Backlight output shorted to ground====
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| *Find and replace shorted component [[How to find short circuits]]
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| **Ensure the short is not caused by the display. Be sure to measure with and without the display connected.
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| **Most commonly, a short on backlight output is caused by a shorted capacitor.
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| ====Device has backlight output on a known good display, but not on the originally installed display====
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| *Replace the display assembly. Use only a display for a A2337 MacBook Pro. '''Earlier Intel MacBook displays will not work.'''
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| ====Backlight fuse (FP800) blown in the absence of a short to ground====
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| *Replace the backlight fuse with a fuse from a donor board or a compatible replacement.
| | Inject 1 V (increase if no reaction), watch for hot spots with thermal cam. Usually it's a bad tantalum cap on the PPBUS_G3H rail. |
| **0603 package size, 3 amp, 32v fuse. Brand does not matter.
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| *Before applying power be sure to double check for a short to ground. Check for a short to ground on backlight output and backlight input.
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| ====PP5v_BKLT_A or PP5v_BKLT_D absent or low==== | | [https://www.youtube.com/watch?v=PDKlWu1eDFA Example video] (Taking 20 V, 0 A. Ethanol used instead of thermal cam with 0.8 V on PPBUS_G3H, resistance between PPBUS_G3H and CPU coil is 3.6 Ω) Example 2: <nowiki>https://www.youtube.com/watch?v=TZsvvUWUInE</nowiki> (Taking 20 V, 20 mA. Bad capacitor located via visual inspection) |
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| *Ensure PP5v_S2 is present to both resistors prior to replacing any components
| | Read the resistance from PPBUS_G3H to Vcore coils (coils around CPU/GPU) IF those measure UNDER 1 Ω (0.3–0.8) then you most likely have a direct 12 V short to CPU/GPU. On this board this situation is always a no fix. |
| **If PP5v_BKLT_A is absent or low, replace RP845 and UP800.
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| **If PP5v_BKLT_D is absent or low, replace RP844 and UP800.
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