Hi,
I am trying to track down a short on a computer board. With power source disconnected, there is almost 0 ohms reading between +5 volt "line" and ground.
There was a device called "LeakSeeker" 82B that was designed for tracking down a short. Has anyone used this or any other device, or do you know a technique?
Thanks in advance, Brad
Before you type your password, credit card number, etc., be sure there is no active keystroke logger (spyware) in your PC.
Power to ground shorts can be a bear to trouble shoot sometimes. I assume this board worked at one time and if so I suspect it is a defective device rather than a manufacturing defect such as a solder bridge, reversed component, pwb fault, etc.
I would try the following:
1) Inspect the components for any sign of overheating. You might even try sniffing around in different areas of the pwb for the smell of overheating. 2) Briefly apply power to the board using a current regulated power supply (key word is briefly) and feel around for overly warm parts or signs of smoke. When I worked in industrial electronics one method we used was placing a sheet of temperature sensitive liquid crystal on the board to locate overheating devices. Try Edmund Scientific for a source if they are still in business. 3) There is a gadget called a Toneohm made by Polar instruments that has several troubleshooting modes for locating various type of short circuits. I don't think you'd be willing to pay for one though. 4) If you find a suspect device disconnect its power lead and apply power again to see if the short goes away.One other thing to keep in mind is the measured resistance between power and ground on some circuit boards is naturally low. Be sure you really do have a power to ground short.
I'm sure there are other methods you could use but this might be enough to help. Good Luck Rush
I used to use a Tektronix Hall Effect scope probe for DC current.
Use an ESR meter or another meter capable of very fine low ohms readings. I think I have heard of a device with a tone of some sort to provide an audible reading.
greg
I would progressively cut tracks. I am aware, but not used, a 4 probe system in the manner of a traditional Wheatstone bridge to monitor differential voltages and so currents in tracks.
-- Diverse Devices, Southampton, England electronic hints and repair briefs , schematics/manuals list on
What is this computer board? Please be specific. If a motherboard I'd start by isolating the power FETs.
I use a Toneohm 850A. But even that can be tough with extremely low resistance power planes.
Problem would be that most computer boards have internal power and ground planes.
I use my Fluke 8050 for that. It has the resolution at low ohms to do it. It also has an mho function but I have not found it to be necessary.
A good ohmmeter that can resolve the resistance of the traces on a circuit board is what you need for the most efficient solution.
JURB
I've used one recently - it's like (I imagine) playing a Theremin (but with contact probes). There's also an LCD display for the low ohm value. As I recall, it wasn't a slam dunk finding the short, but the indications were strong enough to identify the most likely suspects.
Depending on how close to zero ohms your reading is (and the resolution of your meter), you might be able to find the location of the short by walking the probes around the board (on decoupling caps and other 5V pins) to see whether the reading gets even closer to zero.
TM
TM
THe problem is that digital PCBs often have power and ground planes. The sheet resistance of these is so low that finding the location of a short is going to difficult based on resistance alone.
It does work on PCBs with separate power traces - like my Tek 485 when it decides to pop a tantalum cap. :)
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It would be good if you would keep the answer in the same thread as the question. news: snipped-for-privacy@news.verizon.net
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