Author Topic: [Resolved] My first preenFM2 metal case .. trouble shooting no audio  (Read 7492 times)

horridus

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Will do!

horridus

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Ok, de-soldered, then carefully re-soldered all of the pins that match the preenF405 to the DACs on both sides (all 3 chip sockets) ... Used an oscilloscope to view the preenF405 spi_ck and on both DACs ... The clock signals are solid and appear the same on both sides. The 2.5v pins on the DACs still read 3.99v each ... resistors also read 4.02v still .. so no audio / no real change. I tested continuity after re-solder and the signal is clean on all pins preenF405 to both DACs. I used a different voltmeter this time too :>)

horridus

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I just switched out both DACs with new chips from Mouser ... same results

Xavier

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If the digital audio signals from the preenFM to the DACs are clean and if the analog audio signal path after the DAC is OK too. There should be sound  ;)
Unless your problem comes from the mixer/soundcard you use to hear the sound, but as you hear a "Pop" when switching on, it seems to be OK.

You're talking  about the clock signal. It's one of the 5 i colorized in audio_spi.png picture.
I'll try to post this week a screenshot of each of the color showing what you should have.


horridus

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Sounds good ... yes, the pops are perplexing. They don't happen every time though. Somewhat intermittent. They are in time / sync with the flashing LEDs on boot. Yes, the signal between preen and DACs are strong. I have the board layout to look at now. I'm going to carefully trace the full length of the audio signal path after DACs again. The 3.99v at the DACs 4.02v at the resistors seems like the best (only) clue so far. I tested midi via DIN again the other night too .. still works like a champ.

horridus

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I just removed both DAC dip sockets, cleaned the pads nicely, and replaced the sockets with machined sockets. Also new DACs. Still no change. Same 3.85v on the DACs. Next I'm going to remove and replace every resistor and cap on the board. The only ones that look like they may be odd are the 115k resistors. I'll have to locate some though. My local electronics store didn't have any in stock. I have everything else here now.

Xavier

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Sorry, didn't have time to post SPI oscilloscope screenshots.
But if you post yours i can tell you if they are good.

You removed the DAC sockets  :o Ouch. Impressive...

The 115K resistors (with the 1.8K ones) are only to add the 2 DACs output : with a 64 times ratio (115/1.8 = 64).
I don't think they can be responsible for the bad voltage.

Didn't you try to build the other preenfm2 you have ?

« Last Edit: October 04, 2015, 04:46:54 PM by Xavier »

Xavier

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Here are the expected signals measured directly on the pins of the MCP4922 while the preenfm2 is turn on without any sound.

Colors correspond to Audio_SPI.png:
http://ixox.fr/forum/index.php?topic=63509.msg65602#msg65602
« Last Edit: October 04, 2015, 04:42:47 PM by Xavier »

Xavier

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And the 2 last...

horridus

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Hi Xavier,

Nope, waiting until all paths are exhausted in troubleshooting before moving on to another build. I have hope that this one will work eventually. The socket removal was a bit of work, but the sockets come off safely (no pads harmed) if one carefully crushes the plastic around each pin carefully. This saves hitting the pads with a lot of heat for no reason. I have a pretty decent desoldering iron here too. Anyhow, it came out clean, and I wanted to see if any of the pads were somehow connected by excess solder underneath the sockets on the top side of the board. This was not the case. They had (still have) plenty of clearance.

Thanks for the tip on the 115k's .. I'll let them be. I'll look at the oscilloscope today too and compare your pics to the signals here.

Thank you for the pictures too! Maybe by the end of this thread, there will be some good troubleshooting tips for some other novice / future builder of the preenFM2.

horridus

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Handheld pics ... not using a desktop capture app  :-[

Pins 3,4,5 on the DAC side


The last 2 pics you sent, which pins are they representative of?

horridus

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...

horridus

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Xavier

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The last 2 pics you sent, which pins are they representative of?

The file name of the screenshot is the color you see on the SPI schema.

Xavier

horridus

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Ahh, I see .. thanks