ESP32s can't detect/mount microSD card

[mikewax]

well my board is an ESP32 cam module with microSD card socket. The esp32s can't mount the card. using the latest arduino software, I installed the board file esp32 by Espressif Systems according to these instructions.
i reformatted the card as FAT32. i loaded a webserver sketch onto the board and it worked fine. but i've tried many sketches for microSD interface and gotten nowhere.
i simplified the code down to this:

Code: [Select all] [Expand/Collapse]

1. #include "SD.h"
2.  
3. void setup()
4.   Serial.begin(9600);
5.   if(!SD.begin()) Serial.println("Card Mount Failed");
6.   else Serial.println("success");
7. }
8. void loop() {}

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then i got a meter and verified the connections according to this image. still the SD.begin command returns 0. can't figure out why.