I think what happened is that an inexperienced member on my team plugged a 2-wire motor into a motor port 4 on the cortex without a Motor Controller 29, and ran it. Diode #8 on the Port 4 side is now busted, and Port 4 is now unusable.
The diode looks like a generic diode, with the code 502B written on the top.
*]If I replace this diode with an identical one, would this be considered a illegal ‘modification of electronics’ from the VEX Robotics Competition, or a legal repair?
*]If I am allowed to replace it, what specifications do these diodes have so that I may locate an identical one?
Of course I can simply use a Y-cable, or a Y-cable + Power Expander, but repairing the cortex to the best of abilities is almost always better.
When you get the part compare the voltage drop across it to the existing part before desoldering to make sure it’s the correct polarity.
I think this type of repair falls outside any of the competition rules, it’s unreasonable to be expected to write off a $250 cortex because repair is not allowed. The intent is to return the unit to original working condition.
You can try for an official answer but I have not had much luck with that type of request in the past.
Obviously you can send into VEX for repair, and would be my advice if pressed, that’s the safest way unless you have experience with rework.
I believe the diode is connected to ground and prevents extra voltage applied to the Cortex chip. I think it is a zener diode that breaks down above the logic level voltage (5V?). Then the diode will blow instead of the cortex chip.
Our team also had a cortex with a dead motor port, port 9 in our case.
I replaced the ESD diode with the part above and everything is now good. I had checked the output pwm signal using a scope before I did this and voltage was low so there was no damage to the CPU driving that pin. The diode was also not physically damaged as the one in the picture from post #1 was, but still measured as a partial short with a meter.
As before, I do not recommend this repair unless you have experience with rework or have access to a parent/mentor that is willing to do it for you. The part only measures 2.8mm x 1.2mm so this is not a job for the RadioShack soldering iron.
All the tips are quick release and replaceable, we have several different styles of tweezer style tips used for different packages (although to be honest, for most SMT parts beyond the 0603 and SOT-23 etc. types I have other more expert people do the work). This is not a cheap soldering station, somewhere around $2000.
At home I just have one of these, a Hakko 936.
It has been discontinued and replaced by the Hakko FX888 Dean mentioned.