KC Micro Tronix
Member
I ran across a board that wasted a lot of my time. Thought I would share..
No light on the charger, Power supply showed 100 mA current draw. "red flag" So I immediately thought a problem in the PP3V42 supply or a bad SMC. or some liquid damage somewhere. I performed a through inspection for water damage and found none. With 100mA current draw I (assumed) the PP3v42 was probably ok. Like a idiot I grabbed my thermal not my volt meter to take a look. In the past when I see strange stuff like this from the PS I always find it with the thermal. 100mA is quite a bit of current for this stage in the game. I powered up the FLIR and the SMC was a bright hot spot. I was in a hurry and was was behind for the day. I looked up and asked God why did you give me a bad SMC? I hate SMC's. I looked up at the clock and said... Lets see how fast I can swap this puppy out. I Reballed a doner and it took me 20 minutes. I had to reball it twice because the first time I screwed up and bumped the balls when I was reflowing them to center! I am getting faster at these but they still suck. I have seen the SMC fail before like this and have fixed multiple boards by replacing it. It is not common but it happens. After the SMC was on I did a quick bump with the MagSafe watching the power supply and noticed a instant jump to 300mA and no green light. I quickly pulled the MagSafe. I have noticed when using a power supply the green light is almost instant no waiting like a charger. I said "crap that's not good". 300mA is the wrong direction for no green light. I Grabbed my thermal again did a quick power bump and all kinds of stuff light up. (Keep in mind I have yet to take a volt meter to this board. I am a IDIOT). So looking at the board view I notice that they all had the PP3V42 rail in common. So now...... I grab my volt meter and while measuring PP3V42 I did a quick bump with the MagSafe I saw 7V flash up and I instantly yanked the MagSafe. No smoke but holy crap. 7V is way wong! I Isolated the PP3V42 PS and it was putting out 17 volts! I did fix the supply by replacing U7090 but it had already done it's damage. After the repair to the supply the output was normal 3.4v but still no green light. I replaced the SMC again and nope. I did not see any other shorts by measuring or on thermal but I decided to give up on this board anyway. I could spend all kinds of time chasing this carnage.
Well I guess that is how I learn. The hard way.
Had I saw this voltage first I would of walked away while I had the chance! At least I got some SMC practice in.
Just thought I would share my mistake with everyone.
Cheers.
I marked the board as PP3V42 Surge so I don't grab the wrong parts of it as as donor. I almost don't want to keep it around. I can see it still wasting my time.
No light on the charger, Power supply showed 100 mA current draw. "red flag" So I immediately thought a problem in the PP3V42 supply or a bad SMC. or some liquid damage somewhere. I performed a through inspection for water damage and found none. With 100mA current draw I (assumed) the PP3v42 was probably ok. Like a idiot I grabbed my thermal not my volt meter to take a look. In the past when I see strange stuff like this from the PS I always find it with the thermal. 100mA is quite a bit of current for this stage in the game. I powered up the FLIR and the SMC was a bright hot spot. I was in a hurry and was was behind for the day. I looked up and asked God why did you give me a bad SMC? I hate SMC's. I looked up at the clock and said... Lets see how fast I can swap this puppy out. I Reballed a doner and it took me 20 minutes. I had to reball it twice because the first time I screwed up and bumped the balls when I was reflowing them to center! I am getting faster at these but they still suck. I have seen the SMC fail before like this and have fixed multiple boards by replacing it. It is not common but it happens. After the SMC was on I did a quick bump with the MagSafe watching the power supply and noticed a instant jump to 300mA and no green light. I quickly pulled the MagSafe. I have noticed when using a power supply the green light is almost instant no waiting like a charger. I said "crap that's not good". 300mA is the wrong direction for no green light. I Grabbed my thermal again did a quick power bump and all kinds of stuff light up. (Keep in mind I have yet to take a volt meter to this board. I am a IDIOT). So looking at the board view I notice that they all had the PP3V42 rail in common. So now...... I grab my volt meter and while measuring PP3V42 I did a quick bump with the MagSafe I saw 7V flash up and I instantly yanked the MagSafe. No smoke but holy crap. 7V is way wong! I Isolated the PP3V42 PS and it was putting out 17 volts! I did fix the supply by replacing U7090 but it had already done it's damage. After the repair to the supply the output was normal 3.4v but still no green light. I replaced the SMC again and nope. I did not see any other shorts by measuring or on thermal but I decided to give up on this board anyway. I could spend all kinds of time chasing this carnage.
Well I guess that is how I learn. The hard way.
Had I saw this voltage first I would of walked away while I had the chance! At least I got some SMC practice in.
Just thought I would share my mistake with everyone.
Cheers.
I marked the board as PP3V42 Surge so I don't grab the wrong parts of it as as donor. I almost don't want to keep it around. I can see it still wasting my time.
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