Adafruit 16-Channel 12-bit PWM/Servo Shield - I2C interface

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kwixson
 
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Adafruit 16-Channel 12-bit PWM/Servo Shield - I2C interface

Post by kwixson »

Panic! Saturday I'm hosting a workshop as part of a larger Arduino event and I was counting on using this shield. But I can't get the green light to come on, showing I have power to the servos. How can I troubleshoot this problem? So far I've metered the power supply (trying two different ones) and made sure I'm at 5-6V and that it is, in fact, live.

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Re: Adafruit 16-Channel 12-bit PWM/Servo Shield - I2C interf

Post by adafruit_support_mike »

First, take a look through the tutorial and triple-check every connection: http://learn.adafruit.com/16-channel-pw ... king-it-up

If the power LED doesn't come on when you have a supply hooked up, I'd guess you have the 5v line from the Arduino connected to V+ rather than VCC.

If that isn't the problem, post a photo of your setup and we'll see what we can find.

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Re: Adafruit 16-Channel 12-bit PWM/Servo Shield - I2C interf

Post by kwixson »

Okay, well pictures attached. Not sure what they can tell you. I'm using the shield, here http://www.adafruit.com/products/1411

You linked to the non-shield version. So I couldn't have messed up the connections that bad, right? I mean, it's a shield. What you will see that I did mess up is that I put the 90 deg. headers on backwards, so I spent a couple hours trying to get them off and just got the one, then cut the ends off the next one down the row because I need 5 channels for this project. Anyway, apart from that I followed directions, I think.

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Re: Adafruit 16-Channel 12-bit PWM/Servo Shield - I2C interf

Post by adafruit_support_bill »

What you will see that I did mess up is that I put the 90 deg. headers on backwards, so I spent a couple hours trying to get them off and just got the one, then cut the ends off the next one down the row because I need 5 channels for this project.
That shouldn't cause a problem - unless some traces got mangled. If you post a shot of the bottom-side, we can check it over.

There is not a lot to go wrong between the power terminal block and the servo headers. With your multimeter set to measure resistance, check the resistance between the "+" terminal and the + pad for C2 (the circle next to the power terminal). Also check the resistance between the + terminal and the V+ servo header pins.

Also check the resistance between the "-" terminal and the GND pins.

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Re: Adafruit 16-Channel 12-bit PWM/Servo Shield - I2C interf

Post by kwixson »

Well, *bleep*

Didn't see your post in time to try any of that before I went to my event and demo today. See, Maker Weekend-Microcontrollers: [ event link ]

At the end of the day I plugged it into a 5V power supply that could handle more current than the ones I'd been trying and ... poof! Magic smoke. :(

Will send post mortem photos of front and back tomorrow. Up until then it was a fine day. All the Arduino Experimenter's Kits I got from Adafruit made it into the hands of their respective workshop attendees. Everyone seemed very pleased with them and we all went happily about the business of working on some of the included tutorials.

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Re: Adafruit 16-Channel 12-bit PWM/Servo Shield - I2C interf

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Poof! :(

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Re: Adafruit 16-Channel 12-bit PWM/Servo Shield - I2C interf

Post by adafruit_support_bill »

Looks like the reverse voltage protection MOSFET (the one right next to the power terminal) lost it's magic smoke. I don't see any obvious short circuits there. What is the resistance between V+ and GND? Anytime you desolder something you risk damage to the board. The V+ rail runs right next to the GND rail and if the solder-mask were damaged, it would be easy for a little stray solder to create a short.

If you scrub the residual flux off the back of the board with sow 90% (or better) isopropyl and an old toothbrush, it will be easier to see if that is the case.

It is the least of your worries at the moment, but the last couple of headers (channels 14 & 15) looks like they are a bit solder starved.

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Re: Adafruit 16-Channel 12-bit PWM/Servo Shield - I2C interf

Post by kwixson »

I removed the solder as much as I could with the solder sucker on all the right-angle posts, but only completed the job of replacing the one on the end. That's why some don't look like they have enough solder.

So, is it worth it to try to fix this board? Where do I get a replacement part? Even then how do I diagnose the original problem? Could that component have been faulty from the start and that's why it was giving me problems, and only popped when I put something with more current through it?

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Re: Adafruit 16-Channel 12-bit PWM/Servo Shield - I2C interf

Post by adafruit_support_bill »

So, is it worth it to try to fix this board? Where do I get a replacement part? Even then how do I diagnose the original problem?
You have to diagnose the problem before you know what (if any) replacement parts are needed. You can start by taking a resistance measurement between V+ and GND. If there is a short, cleaning as noted in my previous post may make the cause apparent.

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Re: Adafruit 16-Channel 12-bit PWM/Servo Shield - I2C interf

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Re: Adafruit 16-Channel 12-bit PWM/Servo Shield - I2C interf

Post by adafruit_support_bill »

Well the meter reading is pretty conclusive. The question is where is the short? I don't see anything suspicious on the solder-side of the board. There is not much else to the V+ part of the circuit - just the polarity protection MOSFET and the indicator LED. We could replace the MOSFET, but it would probably just burn up again.

If you contact [email protected] with a link to this thread, we can send you a replacement shield.

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