Cortex - H Bridge broken in EasyC

Our brand new cortex has only done once competition, and as we were practicing yesterday one of the high strength motor ports stopped working and smoke came from the sensor ports along with a burning electrical smell… i think we may have broken an H-Bridge but we are using a new version of EasyC so i dont know how… As i said, this is a brand new cortex that we put on for the New Zealand nationals a couple of weeks ago and has hardly been used… for the meanwhile we have changed back to the one we have been using all season (we changed it just to be sure nothing would happen at nationals and worlds)

What can we do? Can we get it repaired?

any help would be appreciated


If it’s still under warranty, you can contact Vex in the USA to get it RMA’d - go to their website and get their phone number, and you can use google to call them for free. Just remember to check the time in Texas (I think you need to call before 10am NZDST Tue-Sat or otherwise they’re off work).

thanks, we got it about 3 or 4 months ago but only opened it about 2 weeks ago

As far as I know the warranty is 3 months after shipping (someone please correct me if I’m wrong) - also not sure if they’ll cover it if the Cortex 'sploded because of something you did, but it’s still worth a try.

ok, today we FRIED A SECOND CORTEX. but we found the problem, a high strength motor had a short circuiting wire… i didnt see this when i checked the robot over… no we have 2 cortexs with one 2 wire motor port which only powers a motor one way… what i now want to know, is if it is repairable - and at what cost?


Not user repairable.
Check with Vex, about both the motor wire and the 2 cortex.
Your type of example problem happens must more frequently in the BEST robotic program where we have student ad-hoc wiring:

  • Lesson Learned/Best Practice: Don’t use ports 1,10 on the Cortex if you can avoid it, and use them for 269’s rather then 393s. If you blow an Hbridge in a #29 dongle, its just a $10 problem, Rather than a $150? Cortex problem.

I winder if vex saw this problem coming?
Built-in 2 wire ports actually being BAD…
Gonna warn our other teams using cortex
Best of luck with ur cortex :frowning:


How was the motor short-circuiting? Was the wire damaged, the pins bent/touching something they shouldn’t, etc.?

A couple of days later, we think something similar might have happened to us. We had our lift (with nothing on it, so not a weight/torque problem) plugged into ports 2 and 9, controlled with two buttons, and it will go fine in one direction, but works intermittently (very intermittently) in the other direction for any motor plugged into both ports. High strength motors were plugged into both ports before the issues occured. We didn’t notice any smoke or electrical smell, but it might have happened without us really noticing.

We’re going to try calling Vex tomorrow… =(

The H-bridge in the Cortex are not protected against motor leads shorting.
Probably the #29 MC dongles are not either.
Anyone know if Victor speed controllers (FRC) are protected against output shorts?
Or Jaguars from TI (was Luminary Micro)?

2 wire ports are repairable. I’ve done 2 now with similar problems. In one case it was just the driver chips. In the other, the driver chips and one of the gate resistors. The driver chips are IC mosfets, one located on the top of the pcb, the other on the bottom.

Exact replacement parts are available. I can provide details if anyone is interested. And no, I have no problem competing with this repair since it replaces the drivers with ‘factory spec’ components.