EXH Holy grail nano issues - please help debug

Started by tss, January 23, 2017, 05:27:29 PM

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tss

So I have this pedal from a friend and I would like to offer my assistance however debugging is not as easy as I hoped, perhaps someone has some tips or ideas?

Issue - On some rare occasions the pedal actually works as should. However most of the time it does not work. Bypass signal is fine, however when the pedal is engaged (LED on) a small bit from the bottom end of the signal is clipped + there is no reverb to be heard. The potentiometer that is normally used to set amount of reverb acts as a volume knob.

I have located the 3.3V switching regulator CS51413 and the output to the digital part is stable and clean around 3.3V.
Another thing that I have noticed is that the normal current consumption is about 100mA from the 9V source, at many cases this will fall to about 60mA when the pedal "craps out" on me.

The regulator is rated at 1.5A so I don't think anything is shutting down. I'm not sure what else to check.

Thanks!

Update -

I have checked the voltages to the DSP chip under 100mA when the pedal works and under 60mA when it does not. The DSP has two supplies of 3.3V and 1.25V.
These connect this way:

PLLA_VDD 3.3V
PLLP_VDD 3.3V
PLLD_VDD 1.25V
CORE_VDD 1.25V
IO_VDD 3.3V

The outputs from the regulators on board also seems to be fine at all times.

U3 is 1.25V
U5 is 3.3V
U8 is 5V

The next possible suspect is the BB PCM3052 codec.

Update II:

So it does seem like the problem is the PCM3052A codec, sometimes hitting it does result is things starting to work again. I have went over the solder joints but it does not seem that I can do much because the case of the device has the pins under so I can only "scratch the surface". I have also cleaned the board around the codec but all of this made no difference. I have checked the 5V analog + 3.3V digital supplies under normal operation and when the pedal stops working and I can not spot a voltage drop so at this point I would say the power supply is OK. Analog part of the circuit is also OK.

Is there anything else to do or this one is going to the glue factory? swapping out the codec is nearly impossible.