stm32f103c8t6 short cuts after programming!

[HSaee.1]

Hi, I am trying to make a circuit with stm32f103c8t6 and a nrf24l0+. I attach my schematic if pcb layout needed tell me to upload that. One of the circuit work good ( the send one) the other one which is identical does not.

after soldering I did check if any short cuts happen there was not any short cut, everything was good but after I power it up and connect the stlink_v2 and programming it ( it did it just fine) I tried to work with but it act abnormal

(especially timings) after I check for vcc and gnd pin I get 124 ohm or lower impedance on them I did it with other PCBs too but same thing happens.

My regulator , regulate voltage on 3.3 volt.

st_link_v2 work I could even program this 124 ohm stm32f103c8t6.

In other PCBs impedance reduce to 20 ohm.

The files are for altium designer .

send works but revive act abnormal .

[TDK]

The schematic looks fine to me. If impedance between 3.3V and GND dropped from ~10kOhm before to 124Ohm or 20ohm after programming, definitely indicates an issue. Make sure rails are stable, especially on powerup. Check for solder bridges.

Do you know what is causing the low impedance?

[HSaee.1]

Hi, before I power it up after soldering I checked for bridges and impedance of it was 1.88k ohm but after I power it up and connect to it the impedance drop to 120 ohm.

And interesting thing is that when I leave it (for 24 hour ) the impedance get back to the 1.88K ohm but again when I power it up and wait for some second and cut the power and measure the impedance it show 120 ohm again.

Is it possible that my electrolyte capacitor get to the problem when I was solder them? because time change the impedance and the voltage drop it.

THANK YOU FOR YOUR RESPOND;)

[HSaee.1]

Hi, before I power it up after soldering I checked for bridges and impedance of it was 1.88k ohm but after I power it up and connect to it the impedance drop to 120 ohm.

And interesting thing is that when I leave it (for 24 hour ) the impedance get back to the 1.88K ohm but again when I power it up and wait for some second and cut the power and measure the impedance it show 120 ohm again.

Is it possible that my electrolyte capacitor get to the problem when I was solder them? because time change the impedance and the voltage drop it.

THANK YOU FOR YOUR RESPOND;)

[TDK]

> Is it possible that my electrolyte capacitor get to the problem when I was solder them

That is one possibility. See if it gets hot while powered, or unsolder it and re-check.

[HSaee.1]

Hi, I did change the cap but it did not work!

I soldered another stm32f103c8t6 board exactly same things happened there was not any short circuit and impedance was good.

After I program the mcu it shows the short circuit and it could not connect to st_link any more!

In all my design I do not have that 1M ohm resistor on the crystal and maybe it is because of that!

I am confused I really do not know what should I do!

[HSaee.1]

I soldered a 1M ohm resistor and I did changed the MCU with new one but no luck again the same things happened.

I did have 4 mcu now I have 3 board that non of them work!

just one board which it's MCU was for another shop is work I get suspects to MCU because they was cheaper than other shop I order a new one from other shop I wish it just work.

An other thing is interesting to me is that after some time the impedance get high and when I desolder them non of them (MCUs) show low impedance on their pins.

I conclude from top that I should have bridge but I recall that before programming I checked for impedance.

[HSaee.1]

:|

[Piranha]

3,3 V / 124 ohm = 27 mA ... seems to be normal working current. But 20 ohm is the approximate impedance of an output pin - probably software+hardware problem. What is the situation while keeping the NRST low (Reset button pressed)?

[TDK]

You're not making the measurement while the chip is powered, are you? How exactly are you making the measurement?