Help with OSCO pin please!! adau1701
Hello everybody!
I have just soldered my first adau1701 board. The thing is I haven't soldered the i2c yet, so cannot program the chip to test it. The thing is, I measure the resistance between the MCLKI and ground on an empty board, the resistance was infinite, but after soldering the chip, I found out that the resistance between MCLKI and ground was zero, they were shorted!! Do not understand what is going on, I checked all the pins and they were soldered properly, so it was something inside the chip. At the same time when I power the chip up, the voltage on DVDD pin is 1.8v and the voltage on analog input pins was about 1.5v which means that the DSP at least partly works. At the same time, the temperature on the chip slightly increases, which also suggests that it works. Please guys help me, I do not understand what is going on, I soldered one more board with the same result. The oscillator which I use is ABM3B-12.288MHZ-10-1-U-T, two of its pins are connected to GND, one to MCLKI and one more to OSCO. I will include the schematic. Please help!!!
Audio Signal Processors
SigmaDSP Audio Processors
adau1701
Guys... You will not believe but it seems that I found the problem. It turned out that the 22pf caps digikey part number 490-6067-1-ND are SHORTED INSIDE!!! I checked several, with and without soldering, they were all shorted inside!! I have never seen anything like that. Indeed I was not lucky. So just in case, keep it in mind and do not by these capacitors!!
Hello Skfir,
Congrats on your first board you've come a long way on your project. Your experience is not uncommon in this line of work, so don't panic.
Although you have examined the solder joints, have another look at pins 32 and 33. Use an inspection microscope if available, if not a very strong magnifier will do. By the way, a Kalart 2" projection lens (Surplus Shed # L3057) is way better than a simple eye loupe, and cheaper than fancier magnifiers. Soldering at the crystal is another difficulty, we have trouble with these tiny crystals where I work (and we're a contract manufacturer!). By "zero ohms" I assume you're reading well under one ohm, a reading similar to that from directly shorting the test leads. There is nothing inside the chip that would read below one ohm from MCLK to Gnd, so external shorts are always the prime suspects.
Once the short is gone, if you need to test the oscillator and an oscilloscope isn't handy, bring the antenna of a portable radio tuned to FM 98.3 near your board. This is the second harmonic of the MIPS frequency, where a working IC (programmed or not) makes just enough signal to quiet a radio at close range (compare to the results with your evaluation board).
Getting the thing to work is a journey, so persistence pays off.
Best regards,
Bob
HI Skfir,
Congratulations on your new board!
Frequently, small capacitors will short out when installed by hand due to excessive heating; this is common across all manufacturers and I recommend using NP0 or C0G types for best results. I recommend that you use solder tweezers or some solder wick to remove the shorted capacitor(s) and check again for your short. If the short is gone, use wick to clean one one of the pads and then quickly solder down the new capacitor in the single puddle of solder on the other pad. Use fresh solder to tack down the other side. If you have liquid solder flux, I would recommend that you use it on the board to speed the flowing process with the solder.
If you find that two pins of a component are 'bridged' together with solder, apply some liquid solder and heat the joints carefully and the solder should 'run away' from the non-electrical area. Wash the board well to remove flux residue.
Let us know how things go!
Best regards,
Coleman
Thank you Bob and ColemanR!
Since I do not have much experience your advice is really super useful. What is about the capacitors, I removed the caps and short circuit disappeared! So it means the problem was exactly in them. Then I thought that perhaps I overheated them, even in spite of the fact that I didn't use anything hotter than 240-250c. So what I did, I took a fresh capacitor right from the pack and measured the resistance between its two terminals and found 0.001ohm!!! Then I took another one and another one and all of them were this way. So either somebody just made a mistake and put, while packing, ordinary jumpers inside the capacitor pack, or just the whole reel, from which mine were cut was defective. In anyway, it was very weird.
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