Question Help with diode on Apple motherboard ?

Jul 24, 2021
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Hi all!

First time poster looking for some help. Help!

I knocked a diode off my motherboard while trying to remove the CPU heatsink clips. Oops. Now I have a couple of questions I need to figure out to get things working again. See my avatar for a photo with more detail (I couldn't figure out how to attach a photo to this post).

1) I found the missing diode's location, but I'm not sure about the correct orientation. I noticed a square bracket-like marking with a gap one one side of the dislocated diode (labelled D7924 and outlined in red) and its intact twin (labelled D7974 and outlined in green). I'm assuming this square bracket-like marking is a hint at which way to orient the diode. Would this be a correct assumption?

2) Also, now the diode is missing, so can anyone tell me what spec I should be looking for to replace it? It looks like it says 15 or S1. Also, this is on the side of the motherboard with very little clearance, so it's a surface mounted piece a couple millimetres in height, in case that helps in advising on the correct specs for a replacement.

The motherboard is part 820-1900-A by Apple. I tried looking for a schematic online, but no such luck. I'm hoping the missing diode's label (D7924) can provide helpful hints in restoring functionality.

Thanks!
 

velocityg4

Illustrious
Some clear, well lit, high res photos would be helpful. Of the diode, location on motherboard, both close up and full board shots (Micro and Macro shots).

But if still Apple marks the board. Their should be clear markings of diode orientation.
https://www.7pcb.com/blog/place-diodes-silk-screen-marks.php

https://learn.sparkfun.com/tutorials/polarity/diode-and-led-polarity

If there aren't Diode marks. Perhaps a letter and number. I know on old Mac diodes are labeled like D1, D2, D3, &c. I know you said 15 or S1 but I wouldn't expect a diode to be labeled with an S.
 
Jul 24, 2021
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The silkscreen on the board has a number (D7924), but on the diode itself says S1 or 51 or 15 or 1S or SI or IS depending on who reads it. Lol.

I was hoping someone on here had access to a schematic of the 820-1900-A motherboard from Apple, and could tell me the spec and correct orientation of the component labelled D7924.

I believe the S indicates silicon, based on my research. Also based on my multimeter readings (in diode test most) that indicate a 0.796 volt drop across the component's twin in one direction and OL in the other, I believe this is a silicon diode. So I'm getting closer to an answer, but still don't know exactly the right replacement component if I can't find this tiny component in my floor sweepings. Lol.
 
Jul 5, 2021
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If you are really stuck go onto youtube and search " Louis Rossmann " he runs a business in USA fixing MAC's , he also does lots of instructional videos on fixing them , he would know exactly what you need to know , he has access to ALL Apple circuit diagrams and component layouts , he also sells parts that can be got from NOWHERE else even Apple , might be worth contacting him ?

Your assumption about the bracket marking around diode is probably correct , and though the pic is blurred when I enlarge , it looks like you should be able to test orientation versus the other diode , though fitting a surface mounted component can be far harder than it initially looks. If you have never done one before try practising on an old PCI card or something before attacking the motherboard ;) If you are unsure then you could use a good quality silver glue , which is basically ground silver in a lacquer base , used to be used to fix heaters on car rear screens etc very conductive and would easily handle the current you require for that small diode , or you could fit a normal component diode and raise it from the board a couple of mm by bending both legs down at 90 degrees , would make soldering childs play and the component would stay cooler as long as you have clearance there to do it.
 
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Jul 24, 2021
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The hilarious part is that I'm strutting around telling my other nerd friends that I'm basically a Louis Rossmann-level repair tech for partially solving this mystery, and it never even occurred to me to reach out to him!!
 
Jul 5, 2021
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Always worth a quick email , he will probably know what it is off the top of his head ;)
and could suggest a replacement you could source more local to you , though tbh an airmailed diode in an envelope aint gonna cost much .
 

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