Teensy 3.6 board problem

[George1]

Hi,

I have some issues with a couple of older Teensy 3.6 boards. I am unable to connect to and program those and would like to fix if possible.

I looked at the Teensy 3.6 schematics and placement of components on the PCB at https://www.pjrc.com/teensy/schematic.html.

Both boards seem to have exactly the same problem, where diode D1 gets really hot and U3 voltage regulator (LP38691) is mildly hot. To test, I connected the Vin and GND pins to a current limited supply, set power supply to 5 V and then slowly increased the power supply current. The input voltage would gradually increase from 2 to 4 Volts as input current is increased to up around 650 mA and then at some point (1-3 seconds) the power supply voltage would jump to 5.0 volts and current would go down to around 150 mA. The 3.3V pin on Teensy outputs only around 50 mV so something seems to be pulling it down to ground.

I tried searching the forums but did not see anyone with a similar problem. Please let me know if you have any suggestion on what to test next, or if you have any other advice.

Thanks

 

[ninja2]

Before you appled external power to VIN did you cut the join between VIN+VUSB (on the back of the teensy, near VIN pin) ?

Did these boards work in the past?

(BTW the link in your post is to the schematic for Teensy 4.1 not 3.6, although they are similar in this regard, i've attached T3.5/3.6 schematic)

 

[George1]

These boards worked originally, and I never had to cut connection between two pins since the Teensy on my pcb was powered only through the Vin pin.

The link I provided has the schematic for all Teensy versions, and you have to scroll down for Teeny 3.6, but thanks for including it in your reply.

Thanks

 

[ninja2]

Have you read this: Teensy 4 Power ?