Troubleshooting
When powering on Dexter, you should see a series of lights. The processor board has 3 bright LEDs.
- green (labeled "D5") lights when the processor board is getting power.
- blue (labeled "D2") lights when the FPGA is loaded and ready for operation.
- red (labeled "D3") lights during disk access (to the SD card.)
If you don't see any light, the power adapter may be disconnected, defective, etc...
- Check that the power adapter has a light on it. If it doesn't, check the wall outlet, power strip, etc... If it does have a light, check the cord to the robot, and the power connection there. If you don't find any obvious issues, the power brick may be defective, or the MicroZed board may be burned out. Testing the voltage output with a multimeter might be an option.
If you see the green light, but don't see the blue or red light, or if you are unable to connect even if you do see the blue light, check that the jumpers are on correcting on the MicroZed board. These are in the lower left corner, and control how the board boots. To boot from the SD card, the jumpers must be set as follows: JP1: 1-2, JP2: 2-3, JP3: 2-3
The SD Card can be difficult to get into the socket correctly and can easily be partially inserted or just fall out. It is on the opposite side of the MicroZed board from the USB Micro B at the bottom of the PCB, just left of center. If you have a fan installed for the stepper drivers, you will need to remove it. You can't really see the socket to get the correct orientation, so make sure the contacts of the SD card are facing you, and on the top.
When you push it up, it may jam or want to twist to the side. Keep moving it around a bit until you can feel it working against a spring, and moving up and down smoothly then press it in until it sort of clicks, not that you will hear the click, but it will suddenly not press back against you as you lower your finger, and you can press it up again and it will release, then again and it will stay.
For detailed instructions on how to connect to Dexter via the network, see Dexter Networking. Here are a few common errors:
- DDE can ping Dexter, but can not connect: When you are connecting your PC directly to Dexter via a CAT5 cable from the PC network adapter, be sure to set up the properties of the adapter so that your PC is NOT on the same IP address as the robot. If you set it to the same IP, then DDE will see the PC when it pings, but of course won't be able to connect to the firmware in the robot to actually operate.
If the robot doesn't seem to be booting, or you can't connect via DDE or ping, a great way to troubleshoot is by using the built in console port. This will allow you to watch the MicroZed board boot (which it will start to do even without an SD Card) and so you can see exactly where it stops or what error messages it displays. For detailed directions see Dexter USB Connection
If you don't see any messages, even after pressing the reset (SW2) button on the board, then the SD card may be defective, installed incorrectly, or may not have the correct image.
If the SD card has a bad image the system might try to boot, but not complete.
One way to eliminate the possibility of the SD card image being the issue is to just format the SD card using the FAT32 File System. In Windows 10, use the command line tool to access the FAT32 format.. In Linux or Mac, just right click the SD card in the file manager and select format, then FAT32. You can test the SD card in your PC by writing files to it, and reading them back. The details of the drive should show that the File System on it is formatted as FAT32.
Then, to boot the MicroZed card with a formatted SD card, change the boot jumpers to use QSPI which is the internal boot rom. Those settings are JP1:1-2, JP2:1-2, JP3:2-3. Note, the SD card must be inserted, and must be formatted FAT32, but it doesn't have to have anything on it. If you have the main power connection for Dexter plugged in, you will need to disconnect and reconnect it; just pressing the reset switch doesn't change the boot mode.
If you get a blue light after about 10 seconds, and get a zynq> prompt on the console connection (see above), then the FGPA is probably good and the problem was a bad image on the SD card. Be sure to change back to JP1:1-2, JP22-3, JP3:2-3 to boot from the SD card after you re-image it. And if you have the main power connection plugged in, you will need to disconnect and re-connect it; just pressing the reset switch doesn't change the boot mode.
If you still don't get a blue light, and you are sure the SD card is formatted FAT32 and is inserted correctly, then the FPGA board may need to be replaced. You might want to remove the MicroZed board from Dexter, so that only a know good FAT 32 SD card is connected, and then power it via the USB cable from your PC. If you get the blue light and zynq> prompt then the issue is the Green HDR Motor board.
If the robot fails to find home on startup, or fails to complete a trained motion in PhUI, or fails to return to home position during eye calibration, especially if there is a horrible grinding / buzzing sort of a noise for a moment before it comes to rest, then the issue is more than likely low voltage from the wrong power brick being plugged in.
The power bricks used for Dexter are standard laptop power bricks, which are commonly available, low cost, and provide lots of power. However, they come in different voltages and Dexters motors want more voltage in order to move faster. The current "green" motor electronics board (as of June 2021) is rated for 38 volts. The "blue" motor board currently in testing will be rated max 75 volts. Although it will not be damaged by providing less voltage, Dexter will not be able to move as quickly and may "stall" during the motion if a 12 or 24 volt power brick is used instead.
It is easy to swap a PC laptop power brick for Dexters power brick. Please ensure that the power brick you plug into Dexter is rated at 36 volts, 4 amps. WARNING: Plugging Dexters 36 volt power brick into a laptop which is expected 12 or 24 volts can DESTROY the laptop!
When going into a closed loop mode where the Encoders are feeding position information into the FPGA to correct each joint to an exact location, one or more joints may start to shake or vibrate, and may squeal and lose position badly. Here is a video of a customers Dexter in that state.
Most often, this is caused by a problem with the encoder. E.g. an LED or photosensor has come out of the hole in the encoder block, the encoder block has been pulled out of mesh with the disk, a connector is loose or a wire broken, or the encoder is simply not calibrated correctly.
To diagnose an encoder problem, in DDE, from the "Calibrate Dexter..." dialog on the "Jobs" menu, do the eye calibration for the affected joint. Note: DO NOT PRESS SAVE! Here is an example of an encoder which is NOT working correctly:
In this case, one of the two led / opto pairs is not working. Diagnose the cause of this type of problem by removing both LEDs and photosensors, then start calibration, but manually shine the LED's into the opto sensors.
- You may see that one of the LEDS causes either photosensor to react. If that is the case, the other LED is backwards, dead, or the wires are bad, or the PCB is bad or the pot for that LED is turned down or bad. Try replacing the LED. Ohm out the wires (after disconnecting from the main PCB), etc... As a last resort, replace the opto PCB.
- You may find that either LED causes either photosensor to move, If that is the case the issue is mechanical. E.g. the hole is plugged up, misaligned, etc...
- You may find that either LED makes one photosensor react, but not the other. That photosensor is backwards, damaged, miswired, or the PCB is bad or the cable is bad or something. Try replacing it. Ohm out the wires (after disconnecting from the main PCB), etc... As a last resort, replace the opto PCB.
And here is another example of one that is correct (after being fixed) showing the "eye" and the correct center dot placed by the user.
Here is an example of a Sensor that was accidentally pulled out of it's hole in the encoder block:
Replacing it and hot glueing it in place corrected the example issue shown with the eyes above.