CS5340-CZZ ADC white noise troubleshooting

[FranciscoPerez]

Hi,
This is my first post here, long time analog electronics repairer and builder, a customer brought an acoustic guitar amplifier for repairs. The amplifier makes use of some digital circuitry to provide reverb effects, which is producing a high white noise.

Managed to trace down the problem down to U201 /RST Input (CS5340-CZZ) Analog to digital converter. Shorting C222 gets rid of the noise but turns off the amp effects, since /RST input is at low level, of course.

I removed C222 and R201, and the noise was still present. However, with those componentes removed, when I tap U201 pin 9 with anything metal (a multimeter probe, screwdriver etc) Noise goes away and I can get the amp to work as expected.

What do you guys think could be causing this? I'm quite new to digital circuits, and do not have access to an oscilloscope. Replaced R201 with a jumper and C222 with a new cap, but the problem remains.
Thank you for your help.
Best regards,
Fran

[coromonadalix]

unless STC 809    is defective   change c222 and try again ??   rst line  should not affect things like that 

its a power management device

u201 could be defective ??

do you have a scope to check the 5v  line, it could be noisy ...
 you have many filetirng capacitors around u201, changing them could  be  helpful

[Kleinstein]

Having the ADC in reset is not really helping with noise, more like turn off the path.

Connecting the pin to some metal parts may either reset the chips and this way change some settings (e.g. amplitude to small). Another possibilty ,may be connecting the metal part via the reset pin and C222 to ground to keep EMI away from the circuit. It may thus be worth checking the shielding and ground connection.

[FranciscoPerez]

Thank you guys.
Already Changed C222 without success. STC809 should not be defective, since removing R201 and therefore disconnecting the STC809 from the /RST input does not make any difference and the noise is still there. I don't have access to a scope, but I doubt the 5v line to be noisy given the noise is not constantly there, and disapears after poking pin9 with some metal part.

It might well be a defective u201, but hope not, since I'd hate to remove and solder a new one, being such tiny chips.
I'm about to try changing some filter capacitors around U201, as well as playing with shielding around it and see if that helps.

Thank you!
Fran