Troubleshooting Cards ( circuit boards) for shorts 1

[schwarz]

Dear Friends,
While troubleshooting boards [mostly containing logic ICs ]we encounter dead or partial shorts that often load power supply. It is very difficult to trace the short particularly if it is under components or caused by IC. The only way has been isolating 'hot' component or just trial and error method. ATE is ruled out.
Long time back I used current probe from hp for detecting and locating shorts. These are no longer available. I have also thought of using toroid inductor to make sort of detector.
What methods are used now a days? Any probes are available now? Thanks a lot in advance.

 

[melone]

Do a goolge search on "short circuit detector".... Maybe some of those results will help.

 

[IRstuff]

If you can spare the money, an IR imager can do that and more.

It allows you to find this type of hot spot as well as perform a thermal survey of any board or other piece of equipment.

TTFN

 

[schwarz]

Thanks melone. Google search however did not yield the correct answer. Most of them relate to wiring not boards.Please note that the boards have CMOS and other sensitive ICs working off 5V /12V rails.
I would also be keen on solutions actually tried out by members.Has anyone made custom peobe/detector ?
How about school compass ? [ Maybe I should check that myself ]

IRstuff : How much would the cheapest one cost ? Do you know if anyone has tried that ? Generally we use finger touch to isolate 'hot' components.

 

[BrianG]

We use a current probe system called "Pinpoint" to locate shorts. With practice in setting it up, it can locate short circuits down to individual pins on I.Cs. Power rails can still be a bit of a problem if you have multi layer boards with power planes rather than circuit tracks, but it can be done!

 

[Skogsgurra]

schwartz

I have in the lab a black box from Polar instruments. It is called Toneohm 700 Faults Locator. And that is exactly what it does. It has low-ohm ranges and DC voltage with microvolt resolution, a tone changes pitch as the resistance or voltage changes. So it is quite easy to follow the voltage drop using the tunsten tipped probes to penetrate the solder mask. So far, I think that a decent ohmmeter could do the same thing. But it also has a current probe so that you can follow the short-circuit current, even if there are components on top of the trace. I love it.

Try to look for Polar, they may still be in business or locate (sorry) a Fault Locator on the surplus/vintage market.

 

[schwarz]

BrianG Could you pls give sourcing details.

skogsgurra Thanks a lot. I checked out Polar is very much alive. Their latest model is 950 .

 

[Comcokid]

One of the HP pulsers and current tracers is currently on sale on eBay.

http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&item=2545880885&category=25415

 

[schwarz]

Comcokid {/b]HP 547A Current Tracer is the one I used.
I am also in touch with Polar now. Let's see how much it costs.

 

[Heydave]

If you are in a hurry, just apply a current limited power supply to avoid burning stuff then start probing with a sensitive volt meter. I have had no problems seeing enough voltage drop from flowing current to track down PCB and component shorts. I have found shorted caps, copper shorts, solder shorts, and a defective dip switch with this technique.

 

[csneng]

at a previous job I would use a high reselution ohm meter to trace 5v shorts. slite variation in impedance can direct you to what part of the board to look at. this enables you to look at it in a passive state.

 

[felixc]

Schwartz,
I wonder why HP stopped selling the 547A, and why nobody else makes a similar product. Were you satisfied with it? I was looking to buy a used one on Ebay, but I needed to read from people who have used it before. I was hoping that it could help me finding shorts between vias and ground planes, or to find shorted capacitors.
Felix

 

[felixc]

Schwartz, please tell us the ballpark price of the Toneohm 950 once you have it. It looks like they have improved their original instrument. But it does not looks like it's cheap.
Felix