Current Tracer - for findinding shorts in a PCB
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From: Scrim on 5 Apr 2010 20:20 <stratus46(a)yahoo.com> wrote in message news:442f6f03-dad3-49d1-9c5b-7a240a31226c(a)q23g2000yqd.googlegroups.com... 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 Has it ever worked or is this a failure? Are you thinking incomplete etch or shorted bypass cap? G� Thanks for the ideas. This is a high precision board that used to work. Ideally I'd like to have a thermal camera, so I like the idea of trying a digital camera in a dark room. Does it have to be a CCD? I'm not sure what my web cam is (cmos?), but at least the infrared filter is easy to remove and it doesn't have autofocus, so I can set it right with the lights on first. It's a multilayer board so tracing with an ohm meter seems like a bit of a non-starter as I have no idea where the tracks go, and because of it's precision I don't want to cover it in frost, although that's a great idea for another time. I've already repaired an area of board under an electrolytic that leaked. The board was carbonised all the way through, but I think I've fixed that. I've looked at all the tantalum capacitors I can see and they all seem ok. Alan
From: tm on 5 Apr 2010 22:49 "Scrim" <nospam(a)nospam.nospam> wrote in message news:I7vun.199336$ti6.7573(a)newsfe24.ams2... > <stratus46(a)yahoo.com> wrote in message > news:442f6f03-dad3-49d1-9c5b-7a240a31226c(a)q23g2000yqd.googlegroups.com... > 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 > > Has it ever worked or is this a failure? Are you thinking incomplete > etch or shorted bypass cap? > > G� > > Thanks for the ideas. This is a high precision board that used to work. > Ideally I'd like to have a thermal camera, so I like the idea of trying a > digital camera in a dark room. Does it have to be a CCD? I'm not sure what > my web cam is (cmos?), but at least the infrared filter is easy to remove > and it doesn't have autofocus, so I can set it right with the lights on > first. > It's a multilayer board so tracing with an ohm meter seems like a bit of a > non-starter as I have no idea where the tracks go, and because of it's > precision I don't want to cover it in frost, although that's a great idea > for another time. > I've already repaired an area of board under an electrolytic that leaked. > The board was carbonised all the way through, but I think I've fixed that. > I've looked at all the tantalum capacitors I can see and they all seem ok. > > Alan A normal CCD infrared camera will not see the heat you are looking for. Only a thermal imager will do that and they are $$$$$$$ not cheap. Maybe you could rent one? It would be nice if you had the board layout. A good DVM on the mV range could find the short. Or the ESR meter suggested by someone else would work.
From: Wild_Bill on 6 Apr 2010 01:00 I dunno about DIY circuits, but a circuit tracer and milli-ohm meter should be very helpful in trying to find a low resistance path on a board without an schematic. If you're lucky, and/or patient, you might find one cheaply on eBay or elsewhere. Toneohm is one brand name for shorts locators, and I bought one of their older models years ago for about $20 on eBay. The circuit-tracing types of shorts locators generally have a digital display, but the helpful feature is the tone ouput, which allows the operator to test circuit locations without watching the display, as the tone changes as the test points get closer to the short. The models I've seen use 4-wire Kelvin probe sets, which allows the circuit tester to ignore circuit component resistance values. -- Cheers, WB .............. "Scrim" <nospam(a)nospam.nospam> wrote in message news:1woun.157498$1j3.78945(a)newsfe10.ams2... > 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
From: stratus46 on 6 Apr 2010 01:16 On Apr 5, 5:20 pm, "Scrim" <nos...(a)nospam.nospam> wrote: > <stratu...(a)yahoo.com> wrote in message > > news:442f6f03-dad3-49d1-9c5b-7a240a31226c(a)q23g2000yqd.googlegroups.com... > 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 > > Has it ever worked or is this a failure? Are you thinking incomplete > etch or shorted bypass cap? > > G > > Thanks for the ideas. This is a high precision board that used to work. > Ideally I'd like to have a thermal camera, so I like the idea of trying a > digital camera in a dark room. Does it have to be a CCD? I'm not sure what > my web cam is (cmos?), but at least the infrared filter is easy to remove > and it doesn't have autofocus, so I can set it right with the lights on > first. > It's a multilayer board so tracing with an ohm meter seems like a bit of a > non-starter as I have no idea where the tracks go, and because of it's > precision I don't want to cover it in frost, although that's a great idea > for another time. > I've already repaired an area of board under an electrolytic that leaked. > The board was carbonised all the way through, but I think I've fixed that.. > I've looked at all the tantalum capacitors I can see and they all seem ok.. > > Alan I've replaced lots of physically leaking 'lytics and where there is one, there are usually more. If you don't initially see the 'puddle', look for brown 'mist' around 'lytics. You might try powering it up and see if you can read the Voltage variations around the board. You might find a single cap that decided to be a wire. Tantalums are known to do this and I replaced one (32 years old) just last week. Monolythic ceramics fail this way sometimes too. Once in 40 years of doing this I had a 'tytic that shorted out. G²
From: Fester Bestertester on 6 Apr 2010 12:42
> 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. |