| Electronics > Repair |
| DIY magnetic probe to find a short? |
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| xavier60:
5amps at 5volts, that's 25 watts!. Maybe the voltage was dropping to something much lower while loaded. I recently started using an AN8008 multimeter with 1uv resolution, cheap also. Just need to be aware of a possible dead spot in the mv range. Mine is +/-5uv, not a real problem though. I use 200ma on laptop main boards to find shorted surface mount capacitors in minutes. I don't follow voltage drops on power rail tracks. I do all of the measuring on the ground plane. it is best to connect the current source negative and DMM negative separately to the ground plane. |
| SaabFAN:
--- Quote from: Old Don on October 20, 2017, 01:13:55 pm ---If you don't have FLIR, apply external power and use canned air held upside down as a freeze mist and find a component that thaws out fastest. Do current limit or you can really toast a board! Pray it isn't in the PCB itself. --- End quote --- Just be careful that the board doesn't crack due to the thermal stress. My method of choice: Infrared thermometer, or moving my hand over the circuit and touching stuff. Most of the time you can feel that there's abnormal heat before you burn your finger. Managed to repair 3 Xboxes this way - It's almost always a capacitor in never devices. In older equipment I'd look at transistors first. |
| Pitrsek:
http://www.linear.com/solutions/5297 |
| GreggD:
Here is my (SHORT FINDER) It works great. If you have a good short it will make NO heat so looking for heat will not work. If the short is between V+ and ground plane you don't have to worry about current going into decoupling caps, it won't, no voltage build up no current. This uses any analog out hall sensor that has an output at 1/2 V+ with no magnetic field. The one I used is out of production. This passes a current of 250mA through the short turning it on & off at about 650HZ. The sensor is on a cable that is passed over the pcb searching for the short. The hall signal is ac amplified about 900 x. U3B and U3D pass the signal non-inverted or inverted synchronous to the 650hz current. So you can run the sensor over a (week) magnet and not interfere with detection. Instead of the output going to a VOM it should go to a voltage controlled oscillator / speaker. |
| Samogon:
If there is dead short, it will definitely dissipate heat and will glow on thermal camera or burning fingers. But if you have unusualy low resistance on some components, camera will show it as normally heated component, may be slightly brighter. Cutting traces and lifting legs or whole components is ol’ school method. |
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