Electronics > Repair


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Hi, if you have a circuit board that you know is faulty but you have no other diagnostics, and the only way of repairing it was to swap out devices from a good board until it eventually works, would there be a specific order of devices to swap out first... i.e, in what order would you swap out the following devices going on prior knowledge of device failure rates:

Processor/ DRAMs, SRAMs, PROMS, ASICs, FPGA's, resistors, capacitors etc etc???

Many thanks,


Paul Price:
The fault in the board may not be due to component failure at all but do a bad soldering joint or contamination of the circuit board, so swapping parts is not your first option.

The least reliable parts would be capacitors, electrolytic types, so this would be my first choice, but your question begs a common answer to a complex problem that requires a different judgement in each case.

In general, power handling components, things on the circuit board that get hot, or handle the most current, such as filter capacitors and power resistors, all things running hot, are the most prone to failure. Also the interconnection technique, the connectors connecting this board to its host are more likely to become damaged than other components on the board.

A careful visual inspection is a must before reaching for the soldering iron.

Hi Paul, thanks for the reply. I agree swapping devices out is not ideal but it does (eventually!) work... I guess I'm looking for a quicker & more technical method of repair than just swapping devices!

Paul Price:
Maybe I or someone else could help if you gave a schematic, picture of the board and the type of failure and the purpose of the board in question.

There's plenty of better ways to fix a board, but you'll need to know more about it than simply "does it work? Y/N".

You'll need, at the very least, to know what it's failing to do a working board would do correctly. Is it, for example, getting hot? Generating incorrect data? Is there a signal that's going out of range? Do the correct lights come on? What criterion exactly is being used to define the card as "not working"?

Without that information, you're stuck. You could swap the parts that have a finite design lifetime (eg. the caps), or perhaps those which connect to external equipment (most likely to have been damaged by outside influences), or those which are most difficult to solder correctly and reliably. Without knowing what fault you're trying to fix, all are equally valid and all are equally likely to be a waste of time.


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