Hey everyone,

I've been using the LPC1768 as a prototyping board for our IEEE micromouse project, and as of yesterday I can't get it to respond to anything. I'm not a seasoned electrical engineer, so I'll try to describe the symptoms to the best of my ability:

-It was running a variety of programs just fine earlier: controlling steppers, sensors, etc. But as of yesterday I can't even seem to get a basic Blinky program running (the LEDs seem unresponsive). I can check the contents of the memory when plugged in via USB, and all the .bin files have transferred successfully, but after pressing reset, nothing happens.

-When I took my multimeter and checked voltage on each pin, they all seem to be at 2.18V, regardless of what any code specified.

I'm very confused, and if anyone's able to help, I appreciate it,

S

Maybe that wasn't meant literally, but some hardware things to check:

• If pin 1 (GND) is showing 2.18V your ground connection has come adrift.
• If the voltage at pin 2 (Vin) is showing 2.18V your external power supply is broken. The mbed needs a raw supply of between 4.5 and 9 volts. [Unless you are powering it only from the USB plug - in which case check pin 39 (Vu) for +5 volts. If it is 2.18v, your USB port has issues.]
• If pins 1 and 2/39 are correct, check pin 40 (Vout). Should be +3.3. If less than that, some huge load is present. Check everything that is externally connected to this pin on your protoboard.
• If all the above is OK, make sure pin 4 (nReset) is at +3.3V so that the mbed is definitely released from the reset state.
• If still not working, try unplugging it entirely from the protoboard, putting in on an insulated surface (piece of paper), and connecting just the USB cable. If it works, then you at least know that something on the protoboard is causing the problem.

I assume you have checked out Simon's page on deadmbeds? http://mbed.org/cookbook/deadmbed

Thanks Hexley for the suggestions, here's what I've found:

I should have been a little more specific on the "each pin is 2.18V", I did mean just the numbered pins (i.e. p5 - p30). I took these voltages when being powered via USB, and the nR is showing about 3.19V, which seems close enough when considering the cheap multimeter. The Vout and Vusb are both working okay too at 3.3 and 4.8V respectively.

Sadly, I was also taking these measurements with this 1768 just sitting in an empty breadboard, so there's really no other hardware that could be compromising the values I measured.

From reading some other entries in the forum, it sounds like the problem may be in flashing the bin file. I'm able to transfer the bin files to the mbed, but when I press reset after the transfer, the Status LED fails to blink, which might suggest a problem loading the "XXXXXX.bin". I have since tried reformatting it, updating firmware, but no luck. It also may be worth noting that some times during file transfer, Windows explorer would freeze and terminate the transfer, which may have corrupted the bin files. I'm not sure how this would affect the board itself, though.

Thanks again for the help!

bump

I have exactly the same problem with my mbed, used the mbed already for different projects and never had any problems. It looks like everything is working except the lpc1768 chip. Thought I didn't made a mistake, but it hapend when I was using a 2 cell LiPo battery as power supply. Mebay I accidentally connected it to the Vb pin instead of the Vin pin?

Did some more measurements and it is not the reset button, 3.3V on the nR pin and 0V when the reset button is pressed. Vout is also 3.3V and Vin 5V if the mbed is connected to my PC with a USB cable. With an extrenal power supply my mbed only pulls about 90mAh, so I think the lpc1768 isn't running. The lpc1768 it isn't shorted, but the strange voltage levels worry me. All the GPIO(p5-p30) pins are on 2.17V, but when connect to ground with a resistor de voltage drops to 0.4V. If the lcp1768 doesn't boot or run because of a bad flash, the I would not expect the strage voltages on its GPIO pins.

I have a question for you, Does the PC interface still work, as flash drive, And the single LED, Flash when downloading ?

If so then you should be able to replace The LPC1768 chip.

ONLY FOR THE BRAVE

Remove, by using a scalpel, to cut IC legs off, Then remove plastic part, Then using ball of fresh solder, wipe legs off PCB.

Clean pads with solder brade, Fit new LPC1768.

CERI