Electronic – Troubleshooting/debugging PCB


This may be an off topic question, but I'm sure many of you have the knowledge and experience to help out here.

A quite complicated motherboard was flexed. The resulting symptoms include cross-talk or noise on some data lines going out to the display. The symptoms get worse when lots of video data is transferred. This could be due the fact that more data is getting transferred and therefore more data is getting corrupted by the noise or it could be due to the SMPSs working harder to power the GPU resulting in more noise. It could be a combination of the two, but at the moment I suspect a bypass capacitor on one of the SMPSs on the motherboard either cracked or the solder holding it on cracked.

Question: Besides a visual inspection with a microscope, is there a way to test for a faulty capacitor/solder joint that likely failed in an open state on a PCB? A hairline crack in a SMD capacitor or in the solder joint somewhere on a large PCB seems difficult to find through visual inspection.

Best Answer

Don't flex your boards. A cracked solder joint on a rigid part is possible. Look for rigid parts with the along axis aligned across the "bow" of the flex.

There is very little chance you will catch this visually since the fracture is just a tiny crack, and with the board returned to its normal shape it probably mostly closed up such that it will be very hard to see.

The easiest fix is probably to run the whole board thru a reflow oven if you have access to one. Barring that, going around and re-melting all the solder joints might work, but will be tedious. The cheapest solution is to buy another motherboard, and then not abuse it this time.

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