Author Topic: Troubleshooting Path, How to for Beginners?  (Read 1037 times)

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Offline bardiir

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Troubleshooting Path, How to for Beginners?
« on: May 21, 2017, 08:45:23 pm »
Hey all,

a Repair Cafe has opened right next door and as I got some basic experience with electronics and I’m pretty good at soldering I thought I’d go there and help fixing stuff. BUT I’m very bad at diagnosing stuff and this is where I turn towards you. I would like to know how to diagnose a circuit and how to get it working without necessarily having a schematic or anything to work with on the device.

So currently my order of inspection is, aside from common sense trouble shooting like cleaning contacts:
Visible inspection for damage and corroded stuff on the board -> if there is some, remove corrosion, try to wire up / replace damaged stuff
Check for power supply, is there voltage coming out of it that does sound reasonable? -> if no pretty much dead end for me but I at least know that it has to be at least partly the fault of the power supply
Check for cold or ripped solder points or try knocking on the board at various places while having power on the device to locate cold solder points -> totally fixable if found

Some examples for the last meetups:
Navigation Device: Broken Micro USB Socket -> fixed with new USB Socket soldered in
Smartphone: Does turn on, display stays black with a little bit of static noise, has been dropped into water but there is no water damage like corrosion visible on the board, display is correctly supplied with current but does only display static -> give up due to lack of entry point for potentially resoldering bad connections
DVD Player: Always reports „no disc“ -> cleaned laser, oiled up motor, checked power supply and it worked, probably the oil creeping into the motor at that time and lubricating it enough to drop the resistance low enough again to correctly spin up the disc
Yamaha Amplifier: Has a loose connection somewhere obviously, toggles on/off when knocked on the case. After some knocking on the mainboard to locate the fault it went dead completely, I resoldered almost all of the points but it still didn’t work. Probably a broken trace somewhere, but no idea how to track that
Smartphone: Only has left ear audio output, cleaned up the port but it didn’t get much better, resoldered the port but still no improvement. -> no further idea of tracking the cause of the fault

As you can see we get a lot of mixed stuff and considering the stuff is dead on arrival a success rate of around 50% overall is not that bad, but I feel I could do better if I could track down the issues better. With some I got a pretty good idea what could be doable. With others there is just not much I can think of to track down the issue. So I would be very glad for hints or tricks about tracking generic home appliances or mobile stuff for errors that might not be visible at first look.

As for me, I do know basic electrical stuff. I can recognize basic components and I know most of the components on a board by sight, I also can recognize some basic stuff like bridge rectifiers. So I’m not completely lost, but I’ve got very basic electrical knowledge when it comes to more advanced stuff. Which is partly why I’m participating too so I can learn.
 

Offline Seekonk

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Re: Troubleshooting Path, How to for Beginners?
« Reply #1 on: May 21, 2017, 09:35:33 pm »
That got me thinking back to college days when I was repairing expensive high end audio equipment. In their great wisdom where I worked, they allowed almost full access to the service department. One day a guy came in and asked if I got nervous working on the stuff. I told him no, it's not mine.

So, It is more fun if the stuff is not yours. 50% would be quite good working on consumer equipment today.  A friend asked me to look at his DVD player. The power supply section was dead. Problem was they placed the mechanics on top of the board. There was no access and it could not be run if you took it apart.  A lot of stuff is designed to be throwaway with assembly the priority to keep costs down.  And that is before you get into custom surface mount parts.  The golden days of electronics is over.

Form follows function.  There is a logical path to follow.  I always attack the simplest thing first.  That often leads to the seemingly unrelated main problem.  In the real world you see things you could never predict. Some people are good at repair and some aren't.
 

Offline Shock

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Re: Troubleshooting Path, How to for Beginners?
« Reply #2 on: May 22, 2017, 09:51:07 am »
Here are some possible answers to where you got stuck:

Smartphone: Does turn on, display stays black with a little bit of static noise, has been dropped into water but there is no water damage like corrosion visible on the board, display is correctly supplied with current but does only display static -> give up due to lack of entry point for potentially resoldering bad connections

You ideally need magnification. Likely either a shorted component or corrosion under a component, cleaning the PCB regardless is a good idea if you cannot see visible signs. Connections easily get corroded from fluid ingress. Obviously remove the battery and remove other parts that can be damaged while cleaning. Dependent on the display but you need to confirm if it's a logic or back-lighting issue.

Quote
Yamaha Amplifier: Has a loose connection somewhere obviously, toggles on/off when knocked on the case. After some knocking on the mainboard to locate the fault it went dead completely, I resoldered almost all of the points but it still didn’t work. Probably a broken trace somewhere, but no idea how to track that

Common to get BGA soldering failures in gear that gets quite warm under operation like laptops, amps, displays. Next look for hot running components and then interconnections and wiggle wiring looms etc. If you have got an intermittent fault especially a cold solder joint you have to go really gently and be very methodical. As you know now you can get lucky or unlucky. Sometimes you need to apply consistent pressure on power on.

Quote
Smartphone: Only has left ear audio output, cleaned up the port but it didn’t get much better, resoldered the port but still no improvement. -> no further idea of tracking the cause of the fault

Easiest to use an oscilloscope and do comparisons between left and right, easier to also capture if at anytime it comes up. Audio circuits are easy to diagnose at component level as they will go back to an IC but unless you have a schematic or can identify test points (ideally with an oscilloscope) you will only be able to confirm the mechanical faults.

Fixing smartphones is a pretty tall order for repair cafe anyway I can imagine if you start getting successful you will have no end of customers. A repair cafe I saw on TV recently couldn't deduce how to replace a $2 clock movement and just said it was unserviceable.
Soldering/Rework: Pace ADS200, Pace MBT350
Multimeters: Fluke 87V, 117, 27/FM               >>> WANTED STUFF <<<
Oszilloskopen: Rigol DS1054Z, Phillips PM3065
 

Offline tablatronix

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Re: Troubleshooting Path, How to for Beginners?
« Reply #3 on: May 22, 2017, 08:58:03 pm »
A good understanding of power distribution, power rails and voltage generation/regulation is invaluable in finding a starting place for troubleshooting. Or at least that is what I have learned so far, I am a lifetime newb.
 


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