yes, the dual diode for sure is required to be replaced. Order spares along with the regulator.
See attached. Remove both of these capacitors off the logic board.
No power to the board -> check the resistance again on D6902, pin # 3 after these caps have been removed.
We are trying to determine which part is causing this line to be loaded down so much. These caps are not polarized so they can be placed back in either direction after this quick test.
Hi,
I remove the caps and i have around 3.2kohm on pad #2 D6902.
The diode isn't on board, i lost it yesterday...
Thank you
Can you check the resistance to ground of pin #3 of D6902?
These caps that were removed are camped onto pin #3 of this dual diode. We are attempting to confirm if any of these parts are shorted and causing the low resistance.
If the resistance is still low, locate the 3rd cap referenced above by @Piernov which I missed to mention in my list. As a quick test, remove it also and confirm the resistance to ground.
I again tested the resistance to Pad #3 just to be sure and here I am quite surprised with the result.
In fact, the value starts at 30mohm and gradually rises to OL.
Is this normal?
Iput back the old diode to see what happen and now, i have 5.11V on pin #2 and 3.88 on pin #3.
For Pin #1, i only have 0.48V.
Yes, it is normal. At least one of the 2 caps you have removed was defective and causing the very low resistance to ground. The low capacitance cap(s) will not be missed.
If you have a donor cap, be sure to confirm the cap can support 20V (min) since this rail will hit that voltage when it is working under normal conditions. Suggest 25v or higher, if you will be replacing the cap(s).
Next time you replace this dual diode, the diode should not self-destruct. The part was killed due to too much of a current draw for the diode rating due to the shorted cap.
I take the latest diode from my donor board and replace it. Now I see with the USB tester that the card absorbs 0.30 - 0.50A but when measuring the diode, I no longer have the 3.8V and 5.11V...
I end up with 0.30V~ and 0.50~
On the other hand, I feel a little heat now at the level of the U3200 component, which I didn't have at all until then.
Does the card have to be placed back in the mac to find the voltages or should I find 3.8 and 5.11?
It is possible that the cap shorting event is causing this mischief.
Remove all power, check the resistance to ground of D6902, pin # 3 again.
If the resistance is still high (not as low as original testing), then configure your meter into DIODE mode.
Red meter probe on pin # 2 = ANODE (positive side); black meter probe on pin # 3 = common CATHODE (negative side) - the meter should conduct / beep. Confirm it.
Then reverse the meter leads and the diode should block and not conduct / beep. Otherwise the diode is defective.
These dual diodes are well under $1 USD each. Always buy spares.
If the diode is behaving, then the regulator may be causing this dip to 0V.
The regulator @ U6903 may need to be replaced. Sometimes, L6900 also goes out with the party. Each are low cost parts (Aliexpress).
Sorry, my work takes me a lot of time in this return to school after vacation, which means that I can take time to answer... I apologize.
Resistance to ground of D6902, pin # 3 again 0.009 ohm
If the resistance is still high (not as low as original testing), then configure your meter into DIODE mode.
Red meter probe on pin # 2 = ANODE (positive side); black meter probe on pin # 3 = common CATHODE (negative side) - the meter should conduct / beep. : No beep but if i put black probe on Pin #2 and red on Pin #1 : short bip (a second).
The diode was functionnal on donor board.
The previous one had burned, this one seems to have fried. I'm afraid something else is going on, isn't it? I will try to buy some but not knowing the characteristics of these diodes and the Aliexpress seller not answering me, I have not done so yet.
About U6903, is it neccessary to order a new unit ? I find 2 "versions" for the same reference : and this one : "
Which of the two is the correct one please?
Thanks again and sorry for the delay in replying...
I'm going to remove the U6903 to see it but I won't be able to do it until Monday... I've just been called urgently for my child.
I'll post the result on Monday if you don't mind?
Thank you for your patience and the time you devote to me!
Post the resistance to ground measurement of this dual diode, pin # 3.
If I am following this thread correctly, you should have nothing on this pin # 3 (diode + caps + U6903 are all removed) ? So this has to be without a short now.
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