You’ll Flip for This 7404 IC Motherboard Fix


We often lament that the days of repairable electronics are long gone. It used to be you’d get schematics for a piece of gear, and you could just as easily crack it open and fix something as the local repairman — assuming you had the knowledge and tools. But today, everything is built to be thrown away when something goes wrong, and you might as well check at the end of a rainbow if you’re searching for a circuit diagram for a new piece of consumer electronics.

But [Robson] writes in with an interesting story that gives us hope that the “old ways” aren’t gone completely, though they’ve certainly changed for the 21st century. After blowing out his laptop’s USB ports when he connected a suspect circuit, he was desperate for a fix that would fit his student budget (in other words, nearly zero). Only problem was that he had no experience fixing computers. Oh, and it takes months for his online purchases to reach him in Brazil. Off to a rocky start.

His first bit of luck came with the discovery he could purchase schematics for his laptop online. Now, we can’t vouch for the site he used (it sure isn’t direct from Dell), but for under $5 USD [Robson] apparently got complete and accurate schematics that let him figure out what part was blown on the board without even having to open up the computer. All he had to do was order a replacement IC (SY6288DAAC), and solder it on. It took two months for the parts to arrive, and had to do it with an iron instead of a hot air station, but in the end, he got the part installed.

Unfortunately, it didn’t work. He was sure of his diagnosis, and the chip appeared to be installed well enough, so he couldn’t figure out where he went wrong. Upon closer inspection he realized his mistake: he ordered the wrong part. He needed SY6288DAAC, but he bought SY6288CAAC. The difference was his chip was enabled HIGH, while the appropriate part was enabled LOW.

Ordering the correct part would have meant another two month wait, so [Robson] decided to take the nuclear option. He searched in his parts bin until he found a 7404 hex inverter, which he put between the SY6288CAAC and the motherboard. With the inverter in place, LOW becomes HIGH and vice versa; saving him from having to wait on the correct part. He now has functioning USB ports, and learned a few valuable lessons about SMD work and making sure you pay close attention to those model numbers.

This is isn’t the first time we’ve seen [Robson] work around shipping limitations in his part of the world. He recently put together a low-cost PCB mill so he doesn’t have to wait months on professionally fabricated boards whenever he wants to make a prototype.



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