normally, upon power up, the AM335 General Purpose EVM would display "CCCCC..." for a brief period before it moved on to regular uBoot messages etc. Well, it no longer boots, nor do I get any activity at all over the serial port. It clearly isn't booting.
So far we get power at many test points around the processor, though current is only drawn by the clock and ddr (as determined by the test pin pairs across the shunts).
We had external connections to level shifters on the spi0 pins when the failure occurred.
Beyond half-stepping our way through the schematic, does anyone have any troubleshooting tips for this situation? Any suggestion (or, consolation) would be appreciated.
What is the Boot mode selected. On EVM, "CCC" is seen if the Boot-mode has UART as a boot device in the boot sequence. May be there is a change in the Boot mode switch.
In reply to Gururaja Hebbar:
Thanks, but no luck. The switches remain in the position as they were from the beginning, matching the positions indicated in the Quick Start guide.
1. Verify the boot switch settings against the Technical Reference Manual of AM335X.
2. Check all the power supply outputs.
3. Using an oscilloscope check the the 24MHz crystal oscillation. If power supplies are good, but no oscillation, the MPU is probably damaged. Make sure the oscillator is not disabled in anyway.
4. Use the oscilloscope to check the pin11 of U18 (the UART0_TXD signal) at power up.
In reply to Coder:
Thanks for the thoughtful reply.
1. switch settings are verified correct
2. I've been identifying seemingly pertinent outputs of U4 (TPS65910) as they relate to inputs of the U2C(AM3359). Where I get ~1.8 and ~3.3, I'm assuming they are correct. But, I'm also getting just 0.9 V (not the expected 1.2 V) on VDD_MPU and no current flow (as tested across R46). Additionally, VDD_CORE is presenting 0.2 V (not the expected 3.3 V) and no current (as tested across R46). Which doesn't seem right, as VDAC shows a correct 1.8 V but comes later in the TPS65910 switch-on sequence, if I'm reading the datasheet correctly. Could it be just something wrong in/around U4?
3. I'm getting no love from my 24MHz crystal (Y2), but that is no surprise at this point.
4. obviously, nothing.
Could it be just something wrong in/around U4?
In reply to shannon mackey:
Remove R46 and R32. See if the voltages are still 0.9V.
I'm getting, now, 1.09 V on the supply side of both of those resistors. Close for the MPU 1.2V, but not the CORE 3.3V.
I think they both should be 1.1V. The voltages are ok. Use a 2W and 2 Ohm resistor. Connect one side to the ground and the other side to the power supply. Be careful they can get very hot. See if the output voltage drops. If it does, replace the U4. Otherwise the MPU is drawing too much current. Probably damaged.
Also check the decoupling capacitors related to these power supplies, could be some contamination short them out. Try removing everything connected to the board.
Well, darn! U4 stands up to the load just fine. Time to move to Plan-B ("B" as in BeagleBone)
Thanks so much for your detailed assistance!
All content and materials on this site are provided "as is". TI and its respective suppliers and providers of content make no representations about the suitability of these materials for any purpose and disclaim all warranties and conditions with regard to these materials, including but not limited to all implied warranties and conditions of merchantability, fitness for a particular purpose, title and non-infringement of any third party intellectual property right. TI and its respective suppliers and providers of content make no representations about the suitability of these materials for any purpose and disclaim all warranties and conditions with respect to these materials. No license, either express or implied, by estoppel or otherwise, is granted by TI. Use of the information on this site may require a license from a third party, or a license from TI.
TI is a global semiconductor design and manufacturing company. Innovate with 100,000+ analog ICs andembedded processors, along with software, tools and the industry’s largest sales/support staff.