post #301 of 301

I finished my second pupDAC today - I soldered the integrated circuits at the university lab and it was a breeze. Solder paste makes it sooo much easier, just dispense that stuff and wipe the edges of the pins with the soldering iron to get almost machine-quality joints - the hardest thing about the whole process is to get the amount of paste exactly right so it looks perfect.

 

I did have a bit of a scare at first, as the supply voltages were all a bit too low (3.1V instead of 3.3 and stuff like that) and the DAC stopped working after playing for about half a minute. I did some multimetering and noticed the resistance between the 2.5V and ground pads was a constant 280 ohms. I guessed correctly (a rare occurrence in situations like this one) that C11 was to blame. I just KNEW it couldn't have been an IC as I'd inspected everything closely under the microscope and didn't have to apply excessive heat to any of the chips. I desoldered C11 and it was indeed blown, I measured a rather low resistance across the desoldered cap. I didn't have any 100nF caps laying around so I substituted two 1uF X7R MLCCs for C11 and C12, they seem to be doing their job fine. This is actually the first time I've managed to kill an MLCC, and I've definitely abused many of them rather badly.

 

Here are my two "puppies" next to each other - the one I built today is connected in the picture:


Edited by hitman47 - 11/29/14 at 8:59am