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General => General Chat => Topic started by: Watth on November 26, 2016, 02:37:20 pm

Title: Hot air reworking: What I learned
Post by: Watth on November 26, 2016, 02:37:20 pm
Preamble: The problem
A few months ago, I had a big problem: I made a mistakenly inverted polarity while plugin a compatible AC adapter to my laptop. The PC would work only on the battery power. It wouldn't power from the AC-DC brick, thus wouldn't recharge the battery.
I couldn’t afford a new PC; and buying a replacement motherboard was to complicated and expensive.
I then turned to the awesomest bestest ever web community in electronics : (
With the help of user poot36, I could track down the problem to a MOSFET that died. RIP little angel, forever in our hearts.
Hunting for a replacement part
Acquiring the exact part was too long, troublesome. If I remember correctly, it was from sources such as ebay or aliexpress, which didn’t guarantee a genuine part. Nonetheless I easily found an equivalent from more reputable sellers (Farnell and RS, although it was cheaper from the latter).
Replacing the part
Now is the tricky part: the MOSFET comes in the leadless Power 33 package. I was not equipped nor used to this kind of reworking, at that time I had a modest iron with a thermostat on the handle. Although I used it for some basic SMD, it wouldn't do, so alternatively I looked around for shops that did this kind of jobs, but found none.
Investing in equipment
Here I’m lucky my parents proposed to pay for the air reworking I spotted. I bought gel flux (Chip Quick SMD291NL from Farnell) and kapton tape, already had solder paste.

What I learned:
Note: in theses points I might have made wrong assumptions, if so, please let me know!
Training on dead or obsolete motherboard is the best way to start, I deduced:
When it was time to work on my PC’s motherboard, one thing became clear:
Title: Re: Hot air reworking: What I learned
Post by: amyk on November 26, 2016, 03:37:11 pm (