EEVblog Electronics Community Forum

Electronics => Repair => Topic started by: Chriss on January 11, 2018, 02:56:59 pm

Title: How do you make a decision is the uC bad or not?
Post by: Chriss on January 11, 2018, 02:56:59 pm

Hi!
I'm interested on the variate of making the conclusion does a uC is bad or not.

So, lets say we have a circuit with an LCD driver and a uC.
The uC can be whatever uC (I dont ask for a specific one).
The board is bad.
You want to repair it.

Everything looks fine bit the lcd still not working.

So, a doubt is on a defective uC.

How to agree with it?

I do these tests:
1. by using the datasheet of the uC check for power on voltages
2. checking for a shortening on the Vcc and Vss line
3. check for overheating
4. if I have some known output signals I will check with scope that

Is there any more test's what we could do to be more sure about a bad or not bad uC?
What is your method?

Thanks.

Title: Re: How do you make a decision is the uC bad or not?
Post by: Kjelt on January 11, 2018, 03:09:59 pm

Check the reset pin condition (check correct level but also the raise/fall time during power up which is sometimes a major culprit).
Check the oscillator(s) inputs.
Check any outputs (see if the thing has a heartbeat eg if it does something at all).

Sometimes it is just a broken GPIO pin those are the hardest to check find if it is not your own program running.

Title: Re: How do you make a decision is the uC bad or not?
Post by: Chriss on January 11, 2018, 03:17:47 pm

Thank's for the replay.
I will put together a list so we have here a list how to test a uC the best way.

Maybe a hierarchy of the test's would be also nice.

My best regards.