Teensy 3.2 with prop-shield electrical problem

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sealight

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Hey,

I'v been walking through this guide https://www.pjrc.com/store/prop_shield.html with the Teensy 3.2 and the prop shield, and everything worked great until I tried to connect a small speaker to the prop shield.

Since than every time i connect the Teensy+prop shield to the PC it disconnect immediately ( i can hear the sound of the windows USB plugin\out), and it doesn't get power
when i connect only the Teensy without the prop-shield it works fine.

things i alredy try:
- replacing the USB cabel
- switch USB port
- switch to another PC

what else can i do? is't possible that i mes sup my prop-shield?

left pic is without the prop, the right is with. (with the Blink example)

IMG_20180218_183245.jpgIMG_20180218_183308.jpg

thank's,
 
The drop out behavior is indicating a short circuit somewhere drawing too much current - be careful in this condition as it is possible to damage your PC or other USB power supply if they are not smart enough to detect and shut down.

Things to look for are any solder blobs that are shorting things, and then trying to work out which pins are causing the problem. If it is happening with blink loaded to the Teensy then most of the ICs are not becoming active so first steps would be to unplug it and measure resistance 5V-gnd and 3-3V to gnd.
 
thank you for the response.

at first look it seems that all the pins solder ok, but now i checked it again and i think i found a small blob between the GND and the 0 pin on the teensy.
i will check and try to fix it
 
I got a Prop Shield when the AMP was enabled within seconds the AMP chip got warm and then too hot to touch, but it never failed as your does. That never got resolved as to the cause or a solution.

Is your sketch enabling the AMP first thing? Take the shield off and put on a sketch not using the AMP - or anything else - but run a sketch printing to USB and blinking the LED on the Teensy alone.

GremlinWrangler is right - powering it could smoke some or all of the Prop or Teensy or Computer. If you have a continuity meter unplug the Prop and check adjacent pins for shorts - and then pins against gnd and power.

It only takes a couple of wires to power the prop, perhaps wire it stand alone on a breadboard with a protected 3.3V supply - just supply base power - then put power to the AMP pin - and the others ... checking the PJRC page for what they are. IIRC I did that and only when 5V was present on that pin and the AMP was enabled it got hot? So the 5V pin will need power too at some point.

If you have tested everything you can see and if you are daring pull the USB, connect the shield and see it that made it work - not powering anything like the AMP. Check for heat as best you can.
 
so i just ran a continuity test.
the teensy is fine but, i found that that the short circuit is between the GND and the 5V on the prop shield.
i tried to find soldering problems but everything looks fine.

this is the code that is on the teensy:
const int led = LED_BUILTIN;

void setup() {
pinMode(led, OUTPUT);
}

void loop() {
digitalWrite(led, HIGH);

}
Click to expand...

and some pics of the prop shield, maybe you can see something i don't...

IMG_20180222_172916.jpg

IMG_20180222_173237.jpg

IMG_20180222_173202.jpg

thank's again for the help.
 
Working across the internet there is a limited amount to be done. Confirming what you posted before, the Teensy works and blinks to itself with no prop shield connected, with prop shield computer drops out because of excessive current draw. Measuring with a meter there is a short across 5V and gnd? Measuring a prop shield here I got a couple of Meg ohm once the filters charged so certainly something wrong.
Looking at the schematic at the bottom of https://www.pjrc.com/store/prop_shield.html
indicates that as long as the soldering is OK (and the photos do not appear to have anything amiss now) the only 5V parts are the amp and the level converters.

So we have gone down to the lowest easily replaceable part. The next step is to try and cut out or unsolder one of the two parts above and see if the resistance changes. Fault finding PCBs is unfun since every step involves damaging something you will need to fix later. You could try connecting a current limited supply set for about 500ma and use a thermal camera or just a finger to find what gets hot. The most likely candidate is the amp, since it would be designed to drive high currents so something like a shorted output would risk melting the driver transistors into something that short circuits.

The problem is that even if you find the problem the you then need to fix it, and suspect you do not have spare ICs and the tools to do SMT repair so doing this is only worth while for the learning experience.

In terms of what killed to avoid a follow up, without a video recording of everything you did since opening the package hard to say but the classic causes are:
Soldering shorting pins together
Loose wires touching
Soldering cooking a chip and slagging it's internals
Applying power wrong- backards, too much, too little or to the wrong pins
Physical abuse lifting something or breaking a solder joint
Dud part or PCB with short - unlikely since PJRC tests before shipping and this failure mode would probably have killed the test jig in some exciting fashion - common in cheap kits where PCB itself has shorts.
and that old favorite when everything else has been ruled out - ESD https://en.wikipedia.org/wiki/Electrostatic_discharge
 
Thank you very much for the detailed answer. really appreciate it.

from what you wrote i got the conclusion that i probably switched between the " + " and " - " with the speaker.
anyway i think i will try to figure out and fix the problem just for the learning and experience.
and for now i will buy a new prop-shield and be much more careful next time.
 
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