-1
\$\begingroup\$

I was given a project completed by another group, they had left school and I was taking over the project from them, with the information that it is not working properly because "something burnt out or is broken".

The system consists of several electronic devices, which I'm not exactly sure what they are, two of them are microcontrollers.

I figure I can test the system with a multimeter to discover which part is broken and needs replacing. How do I go about doing this? What mode and where should I be looking to probe?

If more information is required please ask and I'll do my best, I can provide a photo if it's necessary, but I'm more after the general process of doing this instead of for my particular case.

Part schematic provided by previous group: https://i.stack.imgur.com/cfW2l.png

Picture of the project:

enter image description here

\$\endgroup\$
13
  • 1
    \$\begingroup\$ 1. Identify Malfunction 2. Determine likely culprit (component or circuit region) 3. Measure signals to see what is off 4. Rinse and Repeat \$\endgroup\$
    – crasic
    Mar 16, 2016 at 1:19
  • 1
    \$\begingroup\$ You were given a half-assed or broken project with no documentation and expected to fix it? Yea, sucks to be you right now. \$\endgroup\$
    – Passerby
    Mar 16, 2016 at 1:21
  • \$\begingroup\$ @crasic how do I do that, I have a multimeter, what mode should I use, is there a chance of causing damage if it's in a certain mode and I start touching things? \$\endgroup\$
    – Aequitas
    Mar 16, 2016 at 1:21
  • \$\begingroup\$ This is the pinout for one of the microcontrollers, where here should I probe in what mode to identify if it's working or not? \$\endgroup\$
    – Aequitas
    Mar 16, 2016 at 1:40
  • 1
    \$\begingroup\$ Also, your assuming, or they were assuming, that the issue is hardware, and not a software fault. \$\endgroup\$
    – Passerby
    Mar 16, 2016 at 2:54

2 Answers 2

3
\$\begingroup\$

You have your work cut out for you. First, you need to understand what the circuit is supposed to do, and that will probably be a bit tricky, but I think I can get you started.

The first thing to realize is that the lower right module isn't doing anything, or at least not doing anything connected to your schematic.

The upper left IC, a narrow 24-pin DIP, it the ATMega, which is apparently connected to an encoder of some sort, probably a quadrature encoder.

The red thing below it is the LLC, which appears to be a bidirectional level shifter.

The lower left IC is the Teensy Basic module. Given the labelling, I suspect that the overall function is to interface a quadrature encoder to a serial interface. I'd guess that the purpose of the board is to keep track of the encoder position and communicate that position serially, with the addition of an external reset pushbutton which allows resetting the reported position.

The first thing I see as a problem is that the Teensy Basic external interface, pins 9 to 12, are not fully connected. It looks as though 9,10, and 11 are connected, although that may just be the picture. Output 12, labelled "ERR" on the schematic seems to be missing. Likewise, output 8, which has no schematic connection, is clearly connected to something off the board.

So, the first thing you need to do is find out just what the thing is supposed to do. Only then can you try to figure out what it is doing, and what's wrong.

I suspect that it connects to an encoder, and when it receives an appropriate command it transmits the accumulated encoder position back to whatever unit issued the command.

\$\endgroup\$
2
  • \$\begingroup\$ Thanks, a lot of helpful information, I'm not sure which pins are 9-12, are they the ones on the right of the left mc(teensy)? they go off the pciture but they connect to the motor control in the foreground. \$\endgroup\$
    – Aequitas
    Mar 16, 2016 at 12:41
  • \$\begingroup\$ Sigh. Google on teensy basic, go to sparkfun, then poke around until you find a connection page, such as pjrc.com/teensy/pinout.html. This is part of what I mean by saying that you have to find out how the thing works. You'll need to learn how to attach to the module, and how to read its program. \$\endgroup\$ Mar 16, 2016 at 13:39
1
\$\begingroup\$

Usually if it looks burnt out, it's burnt out. if you can remove the component, build a circuit around it to test it. Eg. a transistor, build a circuit where if you press a button it changes an LED's state using the transistor.

\$\endgroup\$
2
  • \$\begingroup\$ I've had a close look at everything and I can't see any discoloration. \$\endgroup\$
    – Aequitas
    Mar 16, 2016 at 2:25
  • \$\begingroup\$ This is incorrect, its easy to zap Digital IO pins on an IC or MCU with no obvious external sign that it happened. \$\endgroup\$
    – crasic
    Mar 16, 2016 at 2:55

Not the answer you're looking for? Browse other questions tagged or ask your own question.