Current Tracer - for findinding shorts in a PCB
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From: Robert Macy on 6 Apr 2010 12:53 On Apr 5, 9:49 am, "Scrim" <nos...(a)nospam.nospam> wrote: > Is there a DIY circuit out there for a good current tracer? I have a > valuable multilayer pcb with a short between a power supply line and earth I > can't find. The basic idea is to inject a string of pulses through shorted > circuit and use a small solenoid type sensor to follow the current path > until the short is reached. > > Thanks, > > Alan To find such a short magnetically, you should use a "point" sensor [see below], not a coil. You really need to get in close to the path. Don't go too high, else the GND planes will start to attenuate. The 1kHz to 2 kHz range is fine. Pulsing at a high enough rate will move you out of the low 1/f noise range, and these sensors are much smaller than any coil you can put in there, short of using a SQUID. These people make such a sensor and are knowledgeable: NVE Analog Sensor Catalog, NVE Corporation, 11409 Valley View Rd, Eden Prairie, MN 55344 http://www.nve.com. For the pusling supply, you might even get away with using something as simple as a function generator. When shorted, like clip lead to clip lead that constructs a 1 inch diameter they can supply around 100 mA, and I've measured that at distances of over 3 feet away. Depending on how skilled you are [and determined to make this cheaply on your own] you could do this using your computer's soundcard and coils.
From: Jim Yanik on 6 Apr 2010 14:29 Fester Bestertester <fbt(a)fbt.net> wrote in news:0001HW.C7E0B27300447EA1B01AD9AF(a)news.eternal-september.org: >> and because of it's >> precision I don't want to cover it in frost... > > If it were me, I'd want to fix it via any means possible and worry about > calibration later. > > hey,you can frost it,then bake it dry in an oven. -- Jim Yanik jyanik at localnet dot com
From: Baron on 6 Apr 2010 16:51 Robert Macy Inscribed thus: > On Apr 5, 9:49 am, "Scrim" <nos...(a)nospam.nospam> wrote: >> Is there a DIY circuit out there for a good current tracer? I have a >> valuable multilayer pcb with a short between a power supply line and >> earth I can't find. The basic idea is to inject a string of pulses >> through shorted circuit and use a small solenoid type sensor to >> follow the current path until the short is reached. >> >> Thanks, >> >> Alan > > To find such a short magnetically, you should use a "point" sensor > [see below], not a coil. You really need to get in close to the path. > Don't go too high, else the GND planes will start to attenuate. The > 1kHz to 2 kHz range is fine. Pulsing at a high enough rate will move > you out of the low 1/f noise range, and these sensors are much smaller > than any coil you can put in there, short of using a SQUID. A scrap HDD RW head works well. > These people make such a sensor and are knowledgeable: > NVE Analog Sensor Catalog, NVE Corporation, 11409 Valley View Rd, Eden > Prairie, MN 55344 > http://www.nve.com. > > For the pusling supply, you might even get away with using something > as simple as a function generator. When shorted, like clip lead to > clip lead that constructs a 1 inch diameter they can supply around 100 > mA, and I've measured that at distances of over 3 feet away. > > Depending on how skilled you are [and determined to make this cheaply > on your own] you could do this using your computer's soundcard and > coils. -- Best Regards: Baron.
From: whit3rd on 6 Apr 2010 17:25 On Apr 5, 11:17 am, "tm" <no...(a)msc.com> wrote: [about finding a short in a printed wiring board] > Stick the board in the freezer. When you remove it and apply current limited > power > to the suspected circuit, the frost will melt showing just where the short > is. Great idea! Any old AC wallwart is a good current-limited power source, I've got a bin of those ... around here ... somewhere...
From: Jeff Liebermann on 6 Apr 2010 21:49
On Mon, 5 Apr 2010 17:49:01 +0100, "Scrim" <nospam(a)nospam.nospam> wrote: >Is there a DIY circuit out there for a good current tracer? I have a >valuable multilayer pcb with a short between a power supply line and earth I >can't find. The basic idea is to inject a string of pulses through shorted >circuit and use a small solenoid type sensor to follow the current path >until the short is reached. I use a sheet of liquid crystal material: <http://scientificsonline.com/product.asp_Q_pn_E_3072375> Make sure the board starts cold or at least at room temperature. The reason I only have one sheet is that all my friends (and their kids) have pillaged the rest of my collection. It doesn't work on the component side of the board, but works quite well at locating hot spots on the circuit side. Otherwise, an IR thermometer works well. Try to get the 12:1 optics, not the 8:1. -- # Jeff Liebermann 150 Felker St #D Santa Cruz CA 95060 # 831-336-2558 # http://802.11junk.com jeffl(a)cruzio.com # http://www.LearnByDestroying.com AE6KS |