What about resistance to ground at cathode of D8410? Most common issue with these machines is a shorted tantalum cap on the output.
What voltage do you get on the backlight output? If you have 0, then either Q8400 isn't being enabled or the output is shorted. If you have 12.6V, then Q8400 is being enabled, but the inverter is not switching. A lot of issues on the older A1466 for me (apart from dead IC's) are corroded traces on the feedback path so check for continuity in that area (from D8410 cathode back to the IC via voltage divider R8431/R8432).
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No Backlight Macbook A1990 820-01041
Hello all,
Am trying to figure out this backlight issue with this A1990 Macbook Pro.
Tests performed:
There is no backlight even with a good screen.
Backlight IC is receiving the correct support voltages.
Fuse F8400 ok
Current sense resistor R8400 ok
Backlight IC is receiving 3.3V on enable pin.
Backlight IC receiving voltage from PPBUS_G3H, aprox 12.5V.
Backlight IC receiving 5V from PP5V_G3S
Backlight IC BKLT_SCL and BKLT_SDA both measure 0.545V diode mode to ground
I2C_BKLT_SCL and I2C_BKLT_SDA both measure 0.546V diode mode to ground.
I2C_BKLT_SCL and I2C_BKLT_SDA both measure continuity between LCD connector to R8452 and R8453 although show 4 ohms resistance each.
Replaced ribbon cable from motherboard to LCD board.
Replaced backlight IC U8400
I also measured every single resistor and checked every cap related to IC U8400 and did not find any bad components. I also replaced U8400 just in case with no luck. The only thing I can think of so far which may be the issue is that when measuring continuity of I2C_BKLT_SCL and I2C_BKLT_SDA from the LCD connector to R8452 and R8453 near U8400 measures about 4 ohms each. Probably due to the trace size and distance between the two measurement points but not sure if this could be a factor.
Any ideas you guys could throw at me would be appreciated.
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Hello,
So I this MacBook Pro Retina 15.4-inch (2018) A1990 laptop that suddenly will not charge or start. It was working fine before. It would charge and was starting up normally from sleep. The only thing abnormal is that it seemed to be getting battery health warnings. Maybe a precursor of what was to come. Let it sit in sleep mode for about a week. Now it seems completely dead. Seems like no power at all. No lights, no fans, no screen, no touchpad clicks. Battery charger, which is apple 87w, doesn't get hot at all when plugged in. Charger will charge an iphone just fine though.... -
mb code:820-01827-A;
sn:C02Z349ALVDR;
i9 32GB Ram 1TB
Hi, I found short on one of 6 black nand (total 1TB).
i removed all 6 nand ( voltages all ok) and now i want to program with JC P15 but for A1990 2019 there is only 512GB configuration.
I try A2141 1TB configurazion with TSB4228 but the position on pcb is different ( U9300 and U9400 is no stuff on A1990 but present on A2141 and U8800 and U8900 is no stuff on A2141 but present on A1990 )
macbook with A2141 configuration run on recovery but don't complete it.
anyone can help me?05-26-2025, 09:27 AM -
Good day everyone,
Let me preface this with letting you know that I have a smalltime computer repair shop but do not have a lot of experience when it comes to board diagnostics. I am good at soldering etc but finding the issue if there isn't an obvious burnt component is not my strong suit.
The other day I got a customer come in with a macbook A1990 (motherboard 820-01814-A) that would not turn on and had previously been getting the warning message that the battery needed servicing. (Most folks seem to ignore that message, just like the check engine light in vehicles.)... -
Hey all,
I have an A1990 820-01814-A 1TB with U9100 and U9200 shorted due to the ELC chip. I have TSB 3228 Nand chips to replace, but I don't have the dump file.
Can anyone share the NAND dump files for 820-01814-A (1TB)?
Highly appreciate it!03-12-2026, 12:13 AM -
Hi Gang, Im working on Macbook Pro A1990, the battery connector was torn off during friend trying to replace battery. I soldered on the connector back, and created traces. The battery does charge (according to amp meter), and does power on battery only. But the signal detect line maybe done incorrectly, and the macbook shows "X" over battery icon, and "Service Recommended" on new battery
Can somebody point me to which of these connector pins is responsible for battery detect/data line? Pin 4 on schematic had a nub on the trace, im not sure if that is important,...
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