[Resolved] My first preenFM2 metal case .. trouble shooting no audio

[horridus]

I just tried preenF405 #2 .. and tested the voltages ... 4.02v on the resistors ... 3.95v on the DACs

[Xavier]

Last test of the day :
Power it up by pressing a button.
Check on the display you are in bootloader mod.

Then check one more time the 2.5v. Still 0v ?

[Xavier]

I meant : "Power it up WHILE pressing a button."

[horridus]

Still reads zero .. have pleasant night Xavier

[Xavier]

Seems like the DACs are receiving the signal from the preenF405 firmware when it's running.
But so i really don't understand why you don't hear sound while shortcuting directly to the audio jack while I suggested with the blue/green points above... 

In any case you can double check the area circled in the attached picture.
These are all points used by the audio path. Don't hesitate to heat the points again and remove a little soldering.

[Xavier]

And you turned up the volume pot right ? 

[horridus]

I'll try the audio test with the op amp out again .... Then I'll clean up those points in the circle ... I have an iron just for that ... then I'll try the audio test without op amp again.

[horridus]

Yes, volume is definitely turned up ... the audible "pops" on boot go away when it's down.

[horridus]

Hi Xavier,

Ok, cleaned up and hit all of those audio section solder joints looking for shiny. Took away a lot of solder, checked for voltage (still 4.02v at the 68 ohm resistors / 3.85v on DACs) and removed the op amp and checked for audio (volume all the way up) ... precisely the same results.

Ric

[Xavier]

Not easy...
I attached two pictures so that you can check any potential shorcut between junctions and all contuity.
I colorized the 5v in red, so as your audio path is higher than 2.5v i would first try to see if there is no 5V at some place where it shouldn't.

Then, check one by one every part of the circuit following the 2 pictures.

[Xavier]

Do you have access to an oscilloscope ?

[horridus]

I have 2 oscilloscopes, but no probes! I can work on that though. They were out on loan and the probes didn't return.

After work today, I will carefully go through the tests you've outlined and check to see if voltages / values are correct. No worries about it being easy ... i'm patient and I don't mind checking :>)

Thank you for all of your help.

[horridus]

5v test complete. Most points show slightly under 5v .. More like 4.88v ... The op amp shows 4.88 on the 5v pin, and 4v - 4.02v on all but the pin which is ground (continuity is good on that pin back to the top of the 5v regulator)

I'll check the continuity next ... I took a coffee break for this test, so may be a while before results of the other test.

[horridus]

I ran the round of continuity tests in the green picture. All chime in strong. I checked a couple of times to make sure.

[Xavier]

I would go back to the first idea that the DACs do not receive correctly the SPI data from the preenF405.
Audio_SPI.png  picture in message #6.

Maybe if one of the signals green (Clock) or blue (sample data) does not reach the DAC, that could lead to not null but undetermined DAC output voltage.

Following the Audio_SPI.png picture, try to check and resolder all the concerned pins. DAC + preenF405.
Then see with your oscilloscope if the 5 color signals reach correctly on the DAC pins.
They're all fast signal.
The blue one is the fastest signal : several mhz.