Chosen Solution
Hi, I have a rare problem. Normally i fix a short in just a few minutes. But on this board i have checked several times now, without any luck. I inject from 1 - 4.2A to the pads. Voltage down to around 0.9V, So heat should not be a problem? I use the rosin method, removed all shields and covered the WHOLE board. Can’t find any heated component at all. Any ideas how to proceed?
That happens some times. Heat is a byproduct of power and power is the current times the voltage drop across the component. The voltage drop is determined by the resistance so if you have a very low resistance short, there will be minimal power generated, hence very little heat. Don’t let the value on the multimeter fool you, there is always some resistance in a dead short, usually in the milliOhm range. So consider the following: If you have a 1 Ohm ( 1000 mOhms) short at 1 A, you have 1W of power being generated. If all that power is being generated through one component, you will definitely see a heat signature.At the other extreme, if you have a 1 mOhm short, you now have only 0.001W of power being generated and you will not see that at all, whether you use Rosin Flux or a FLIR camera. There is a new tool out there called the “Short Killer”. You can find on Aliexpress or eBay. It can send up to 30A into a circuit which is usually sufficient for finding difficult shorts.
