What are your thoughts on fault tracing?

Here's a question for all you repair gurus out there: when approaching a device with an unclear point of failure, how do you approach the problem, and what would you recommend is the minimum equipment you require to fault find on a device of reasonable complexity?

The reason I ask is because I have a couple of broken items that have come across my way.

One is a PS3 with a drive that constantly thinks a disc is being inserted (and is probably a fault with the IR transmitter, as the obvious options - such as misaligned mechanism, bad contact on the microswitches, etc. - have all been exhausted.

The other is a Wii U Gamepad that has had a bad life. It arrived caked in unknown substances, the AC adapter socket is damaged, there is a little bit of corrosion on the accessory port, does not power up, and has no response to charging (i.e.: does not power on, and orange light does not come on when put on charging dock either with or without battery in it). It had been previously opened, or at least had it's plastic screw covers removed, so warranty is toast I imagine.

I'd assume there was a capacitor failure, or some fault with the power distribution within the gamepad, but with no obvious power rails, no service manual (being a 'restricted' item) and no online advice for this situation that I can see, it's pretty much a 'investigate the problem, until exhausted'.

I do have a decent understanding of electronics (or at least have a piece of paper from university that says I do ), I have some basic diagnostic equipment (i.e.: multimeter, continuity detector) but I really don't know what the best course of action to take when fault finding, or what equipment is required to make any meaningful progress.

 

I'd just follow the traces from the mechanism you think is causing it or is responsible for it and then testing the component or continuity. At least thats what I would do.

 

The op is clearly looking for more than an overview of the utter basics of fault finding.

 

The minimum in knowledge, experience or equipment?

 

He's asking for thoughts, so I gave him my thoughts.

 

On the ps3, I would drop in a test drive to see if the light turns off. Your fault could be with the drive board or main board. This would point to correct the board. From there, I'd trace back on the drive detect switch.

The wiiu game pad, I'd first look at the charge port. Since you said it was mangled, I'd make sure the solder joint is strong there. I'd then trace from this point to at least the battery light. A esr meter is useful tool for checking caps. Other than that, you just have to have a good base knowledge of electronics to understand how the electricity flows through the board. Which just comes from experience by researching etc.

 

Yeah, that's the route I usually take, and has kept me in good stead in previous fault finding, but the problem is that the Wii U is a more complicated beastie than I'm used to, so starting from one point to another is a little bit more twisty-turny than previous projects. I'm more just looking to find out whether there is 'fault finding-secret sauce' that I don't know about.

Sorry, I meant equipment. I hope I have a decent amount of the other two! Will correct the original post to make that clearer.

At the moment, I don't have a spare drive to test with. However, pulling the power from the drive and powering the console makes the problem go away. In addition, pulling the data line but leaving the power in brings the fault back (albeit without the drive light showing on the console itself).

The AC port is mangled, true, but the gamepad has a secondary charging point on the base of it that is also non-responsive, but I will definitely try tracing along the paths until I found the culprit. Thanks for the heads up on getting an ESR meter, though, I think that might have to be the way to go, as the pad has so many SMD caps in it that a) visually spotting bad ones is a no-go, and b) lifting and testing each and every one is going to be a nightmare.

 

Scope and multimeter are essentials.

Esr meter I wouldn't bother with as an essential, you often need to remove the caps from circuit to get a good reading and if you suspect a cap and have to remove to test it - you may as well replace it.

Money better spent elsewhere if you are setting yourself up.

Bench PSU also handy, as is function generator and a logic probe.