Broken V5 Ports... and How to Fix Them!

One dark night, after blowing the 13th port of a V5 brain due to static, our club finally snapped. After enduring hours of failing autons, lost matches, driver confusion, we officially had enough with broken ports. We decided to identify, and if possible, fix the problem. Our clubs journey led us to purchasing the parts needed to fix this particular brain, successfully restoring the brain to 20 of the original 21 ports after 13 ports were destroyed by static electricity. We also discovered some useful resources and tricks which may reduce static discharge on the robots. After seeing how widespread the problem of damaged ports on the V5 system is in both our competitions and the wider vex community, our club decided to document our discoveries about the issue.

What’s Going on Here?

As most people have deduced by now, static electricity is the main cause of damaged ports. To the best of our knowledge, static electricity is being developed between the metal frame of the robot, and the isolated plastic housings of the motors. Eventually this discharge builds to the point where it can jump to the data lines of the smart port, causing either the motor side or brain side RS485 transceiver circuit to fail. Static electricity is always built on frictional surfaces. Intakes, trays, or wheels can all be sources of static electricity in a robot.

How can We Stop It?

While Vex is now rolling anti-static mats, which should help with this issue, there are several fixes which could potentially help reduce static potential across a robot. First, apply an anti-static spray to all field tiles. This will discourage the build up of charge on the wheels. One example of static spray we have used is Here. Try to maintain metal-to-metal contact between components of a robot. Potential problem points here include screw joints and linear slides. These tend to be supported by bearing blocks, removing all metal interface. We tested this idea by screwing down a bare wire between each isolated component on our robot this year and while we continued to break ports, we observed a reduction in port damage.

About Those Damaged Ports

I must lead this section off with a disclaimer. Repairing V5 components in this manner is NOT condoned by the vex rulebook and is technically against the rules of competition, specifically those restricting modification of motors and brains. This WILL void the warranty of any vex product. All repairs of this nature are taken at your own risk. That being said, this repair will not change the performance of any ports and will not create an unfair advantage since this is only a part swap instruction. The repair in question will change the communications integrated circuit, called an RS-485 transceiver on either the dead brain or motor. This part of the circuit acts as a translator between the smart port wire and the processors in their respective product. These are common parts and can be found on websites such as digikey.com or mouser.com. The damaged chips are located on the V5 brain just under the cover. For our repair, we found the identical part at this Digikey link.

It is worth mentioning that this repair will not guarantee the restored function of a port. There is also a current limiting fuse for short can which can break, disabling a port. This occurrence is much less likely compared to the repair outlined in this post. We never experienced this. Due to the difficulty of soldering, we never attempted this repair. In our test repair, failures were due to soldering error damaging PCB pads.

Identifying Damaged Ports and Materials Required

With those disclaimers out of the way, I will first go through the repair process on a v5 brain. To complete this repair you will need to know how to do surface mount soldering. Useful soldering tutorials can be found at https://www.youtube.com/watch?v=hoLf8gvvXXU and https://www.digikey.com/en/blog/how-and-when-to-use-solder-wick.

You will need a soldering iron with a fine tip, thin solder wire, flux of some form, solder wick and the RS-485 transceiver chips discussed earlier. First, identify all burnt-out ports on the brain by plugging in the brain to a battery, turning on the brain and plugging in a known working motor into each port. If the port is working as intended, the LED on the motor plug will be a solid red. If the port is broken, the motor led with blink and the motor will not be detected in the devices tab of the brain. Write down all damaged ports. It can be helpful to identify the ports later by placing cable ends in the damaged ports to identify them.

Repairing Ports V5

  1. Remove all power and cables from the robot brain, find the 4 screws in the back of the brain holding the two plastic halves of brain together. Remove these screws

IMG_20200223_204344

  1. After removing the screws, the clamshell frame halves can be separated.
  2. Visible are the RS-485 chips we will be replacing. These are attached to the first of two circuit boards in the V5 brain. This board handles power distribution and communicates through a connector to the LCD and compute board of the brain. This board can be removed by gently pulling the board out of the brain at this point.

IMG_20200223_204738

For this repair , I would suggest going no further into the brain unless you intend reflow solder components back on. This is an advanced soldering technique which I am not covering here as I don’t fully understand how to do it. There are a series of plastic parts in the board beyond the mounted parts which can fall out and be lost.

If you will reflow solder to replace the rs-485 chips, follow this paragraph. Due to the fact that a heat gun is used to remove components, you will need to fully remove the PCB from the ABS plastic case of the brain. If you do, first put the screen protector on, keep the screen on the table face down for the entire removal process. remove the four screws holding the board assembly in and take out the main board SLOWLY! There is a flex cable out of view which connects the screen to the main board! Pull the black tab on the opposite side of the flex cable and the board assembly can be removed from the flex cable. The top computational board can be removed by pulling gently and evenly on it. Remove it and the plastic spacer to reflow solder. Keep the screen face down as there are loose plastic and metal pieces present.

IMG_20200223_205325

  1. Identify which chips are to be removed. If you marked the dead ports with cable ends, the ends will be in the smart port sockets in the front of the board. Use the solder wick to desolder the damaged chips and remove them.

RS-485 locations

The bottom right port chip is port 21. The next chip to the left of this one of the above picture is port 10. The upper right port is port 20. The remainder of the RS485 transceivers on the brain follow port definitions on the exterior of the brain.

  1. Clean the pads carefully and tin the pads with solder.
  2. Place a new rs485 chip and solder the pins to the board. Check the orientation of the chip, the vertical bar printed on the side of chip should be on the same side as the other chips in its respective row.
  3. Check all the RS485 chips for bridged pins from soldering. A bridge occurs when solder connects two adjacent pins together instead of to their respective board pad. Touching the iron to these points will usually separate them. Failure to do this step could permanently damage ports or the brain.
  4. Reassemble the brain, replace all screws and power on the brain. The repaired ports should be functional. No further work is required. These devices are integrated circuits, and as such have no firmware.

So We Fixed It. Now What?
I now specifically want to address Vex Robotics. This is a real issue. I believe the design of V5 was intended to protect the larger brain, however the failures of these chips are drastically reducing the functional lifespan of the hardware, sometimes to less than a year. This is unacceptable for an educational robotics platform, especially one which fills this role so well.

One suggestion to the problem which requires little redesign would be to replace the existing RS-485 chips with a dual inline package variant with replaceable sockets. Vex could sell the replacement parts and when a port fails, it would be an easy to service fix for any team. Only four screws would have to be removed to implement repairs. Second, allow students to ground floating metal with wire. This would have helped this year with lifts and other mechanisms that often have floating metal. As I see it, it is not the student’s job with to compromise robot performance in order to not accidentally cripple their robot through static. I think simple repairs with the new anti-static field measures will have a beneficial impact on future years and students.

Edit: I relabeled the picture indicating chip port numbers, they were inverted.

55 Likes

Thank you for the tutorial! I’m probably going to go ahead and take apart one of our brains and finally fix the ports that have burnt out

You also may want to add that the v5 battery under and overvolts when under heavy load, frying stuff instantly, and creating inconsistencies in autonomous. These inconsistencies occur when the motors are not given enough power, or given too much power when trying to run auton code. If you have a newer v5 battery (purchased under 6 months ago) DO NOT try to run “DOOM” on the brain. We tried, and bricked everything.

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Thank you! Thank you! Thank you! I know your fix will likely not be allowed by the rules but simply having a detailed explanation of what was going on is so incredibly helpful. Coaching a younger middle school team, this was a nightmare scenario as their intake motors were constantly triggering ports to die throughout their most recent competition. A frustrating day for sure!! It makes sense now as they had the motors mounted to bearings.

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What

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I have never observed this in our brain. As I understand the voltage controls on V5, Each motor is allowed to draw up to 2.5 amps with 8 motors maxing out the capabilities of 20A discharge rate of the brain. If more motors draw current, the current will be limited among all motors. I don’t believe the battery over or undervolts. Not sure what happened on the DOOM problem. Was vex tech support able to help with this? That sounds like a bad firmware interaction with the game code which should never happen.

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The way to prevent ESD damage from happening is very simple. Three passive components are required to prevent static damage to the RS-485 to UART transceiver chips. The transceiver chips probably cost them about 2 dollars per chip at the quanitity they order them. The three passive components needed are two resistor and a TVS Diode. All these components are pretty cheap and will cost about 60 cents per port or $13 per V5. Also the how to guide for preventing static damage to the chips is like the first result on google. Linked here: http://www.ti.com/lit/ug/tiduai4/tiduai4.pdf

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so your telling me they could sell the V5 for $50 more with those chips and no one would have to complain about blowing ports ever again?

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knowing how much vex likes to mark things up, that’ll probably be an extra 100 dollars for v5.
I don’t know if I’m willing to pay 100 bucks for esd protection

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That’s an excellent write up @V5Wizard!

I think VEX could get those components much cheaper:

Last year I found a deal on EBay and bought 50 SMBJ43CA TVS diodes for about $6 including shipping, which is ~ $0.25 to protect one V5 port.

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100 bucks is a cheap price to pay for not having to buy a new V5

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Especially since VEX slaps their logo on it and says that you now have to pay $275 to get a new one

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Good point. I was just using max quantity cost on mouser to estimate as a rough estimate. They would probably go straight to the manufacturer to get the parts. The point I was making is that its a cheap and very simple solution to a known problem and just looks very bad and sloppy to have overlooked. I think that point still stands if its 0.60 or 0.25 per port.

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Thanks all for the ideas on the anti static. Our club will probably look at a way to make a TVS in-cable adapter. It would be legal in VexU and at the very least could be useful for others up to competition. Vex really should just sell the brain with this added or at the very least, sell a power distribution board with this implemented.

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It won’t be legal in VEXU because custom electronics aren’t allowed to interface to the between motors and V5. I also don’t think you could make an effective in cable adapter since the chips are smd and should be placed on the board as close as possible to the transceiver chips. It wouldn’t have been hard to include it in the design from the start but would probably be pretty hard to add it in now.

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What about grounding the metal heatsink on the motor to the frame of the bot? You could also attach a conductive wire from the frame and let it drag the floor.

The motors do not have a metal heatsink.

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As @sazrocks mentioned, these motors do not have a metal heatsink. The heatsink looking shape on the motor sides are for rigidity of the plastic and not for cooling. Without them , the motor pcb could be damaged. Our club discussed an idea of wiring a ground wire from the circuit board the the metal screw insert in the motors and brain, which would in theory achieve the same effect of limiting the overall static potential of the robot. I still feel the best fix would be for vex to update the power distribution board on the brain with anti-statics components.

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this is definitely worth looking into, since I belive my organization has a brain with 20 dead ports that is out of warranty, as well as several (6?) more unusable brains.

@Arrash opinion?

we currently have 3 unusable brains. they kept whitewashing and had at least 12 ports burnt on each