1
\$\begingroup\$

If I have a multimeter that can measure current, voltage, capacitors, resistors, ..etc., how can I detect the damaged component(s) in a PCB?

  1. I try to visually detect if there are any damaged components such as a blown fuse, broken resistor, black components (due to excessive heat), weak wire welding, or sockets that are uninstalled properly.

  2. I try to find if there are any short circuits using the multimeter. I test the terminals of every transistor, resistor, ...etc.

  3. The worst part is that I measure the values of each component and see if the measured value matches the written value or not. But "loading effect" here is very annoying because I might measure a damaged capacitor but the measurement is close to the right one due to loading effect. I might measure a healthy capacitor but the measurement is incorrect due to loading effect as well.

  4. I don't know how to test ICs.

  5. Sometimes, I meet new weird components that I've never seen before. Of course, I don't know how to test them.

The three approaches that I mentioned are not effective at all especially when it's a big PCB and have a lot of components.

So how can I do effective maintenance to different electrical devices?

\$\endgroup\$

closed as off-topic by Dave Tweed Jul 3 '18 at 16:25

This question appears to be off-topic. The users who voted to close gave this specific reason:

  • "Questions on the repair of consumer electronics, appliances, or other devices must involve specific troubleshooting steps and demonstrate a good understanding of the underlying design of the device being repaired. See also: Is asking on how to fix a faulty circuit on topic?" – Dave Tweed
If this question can be reworded to fit the rules in the help center, please edit the question.

  • 1
    \$\begingroup\$ To be maintainable, "large" PCBs are usually designed for test, and the test procedure for each one of these is documented. \$\endgroup\$ – Eugene Sh. Jul 3 '18 at 16:06
  • \$\begingroup\$ @EugeneSh. So how about the smaller ones like PLC module board? \$\endgroup\$ – Michael George Jul 3 '18 at 16:07
  • 1
    \$\begingroup\$ The most effective tool without experience on IC’s for interface solder issues or damaged ports is a sine wave VI trace on scope comparing a KGB or Known good board. Search and emulate Huntron Tracker \$\endgroup\$ – Sunnyskyguy EE75 Jul 3 '18 at 16:08
  • \$\begingroup\$ Even the smaller ones should be. Unless they say - if it is broken - just buy a new one. In any case, your test has to be tailored to the specific schematic. \$\endgroup\$ – Eugene Sh. Jul 3 '18 at 16:08
  • 1
    \$\begingroup\$ A thermal camera is a good tool to see if any areas of a PCB is getting unusually hot. \$\endgroup\$ – Makoto Jul 3 '18 at 16:18
2
\$\begingroup\$

The first thing I will say is that for a modern PCB, it will often be impossible to repair in this way. You really need a schematic, and oscilloscope, and an a stereo microscope to really "see" what's going on. Even then it will be difficult unless you designed the board yourself and know exactly how it's supposed to work.

One common exception to this is replacing electrolytic caps. You may be able to repair a PCB by replacing blow capacitors, especially if you're repairing something like an LCD TV where this is a well known procedure.

One other failure that's fairly common that you may be able to fix is replacement of a shorted surface mount component (like a MLCC or diode). I have a special trick for this. You can use this method on boards that have a hard short between power and ground that you can't locate.

First you need some kind of temperature sensor, an IR camera is best, but an IR temp gun or just your finger can work too.

Hook up your board to an adjustable power supply, and slowly increase the voltage until you're flowing 1A or so through the short. Now use your IR camera (or finger) to look for hot components on the board. If you find one, then that will be the failed component.

\$\endgroup\$

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