ST-LINK V2 cannot detect STM32F103 on custom board via SWD

[Anh]

Hello everyone,

I am working on a custom board using an STM32F103 (LQFP48) and connecting it via ST-LINK V2 using the SWD interface.
However, when I try to connect, STM32CubeProgrammer reports:

Error: No STM32 target found!

The log shows that the ST-LINK is recognized, the voltage reads ~3.16V, but the MCU cannot be connected.

Additional details:
- ST-LINK V2 wiring: 3V3, GND, SWDIO, SWCLK, NRST
- Tried “Connect under reset” mode and reduced SWD frequency to 50 kHz — still the same error
- The board has a 10kΩ pull-up resistor on NRST and a 100nF capacitor to GND
- Power supply is stable at 3.3V
- Continuity test from the SWD header to MCU pins shows SWDIO (PA13), SWCLK (PA14), and NRST are all connected
- MCU is brand new and has no firmware flashed yet

My questions:
1. Besides wiring and power supply issues, what other reasons could cause ST-LINK to fail detecting the MCU?
2. Is there any way to check if the chip is locked at RDP Level 2 when we can’t connect at all?
3. Are there recommended methods to test SWD directly on the MCU pins to rule out PCB routing problems?

Thanks in advance!

[AScha.3]

Hi,

1. Is your st-link V2 like a stick? 

Then it has no working nrst/reset , try connect mode: software reset.

2. Is boot0 on GND ?

3. If you buy a new CPU from an official distributor, it's not on RDP 2 , because this would be a useless piece of recycling trash.

[MM..1]

Your schematics is unreadable, but chceck datasheet if VBAT can be unconected...