De-bugging PCB having power ground short

[joniengr081]

Hi, we are having some problem with a Microcontroller based PCB having a single power supply +5 V that is supplied by a DC-DC converter on the PCB. How to de-bug if there is power and ground short. There are several components that use the same power and ground and I have no idea how to start de-bugging. Which components to de-solder first in order to trace the problem.

[langwadt]

Hi, we are having some problem with a Microcontroller based PCB having a single power supply +5 V that is supplied by a DC-DC converter on the PCB. How to de-bug if there is power and ground short. There are several components that use the same power and ground and I have no idea how to start de-bugging. Which components to de-solder first in order to trace the problem.

power it up, use thermal camera or alcohol to see what gets hot

[Gyro]

This question comes up a lot, a forum search will bring up lots of threads which may save you some time in waiting for answers.

For those not blessed with thermal cameras, and in the case of a hard short, those that are, the simplest and safest way is to use a low voltage current limited power supply and DMM. Set your bench PSU to maybe 1V and set the current limit to 1A. Connect the PSU across +5V and ground (as close to the DC-DC converter as possible. Then go around the board with a DMM, set to it's most sensitive mV range, measuring the voltage across the active and passive components (start with the capacitors) that are attached to the +5V rail. The lower the reading, the closer you are to the short.

Do not share either supply lead with the meter leads, use both meter probes at each component. This will give you best location accuracy. With a 1A current limited supply, even a 3 1/2 digit 200mV range will give you 100u Ohm resolution. Turn off the PSU before clearing the fault to avoid any possibility on nasty transients.

[joniengr081]

Thank you very much for your comments. These tips are very useful.

[mikeselectricstuff]

If you don't have a thermal camera you can use the "Rossmann method"  - put some alcohol on the board and look for where it evaporates first.