I just tracked down a shorted tantalum in a Tektronix DM501 multimeter. It was on the output of the floating -12 volt supply bridge rectifier before the regulator. The current level was so low that it never heated up although I burned two fingers on the push-pull output transistors for the floating supply. The regulator is on a separate module but the supply was still shorted when I pulled it and the bad tantalum was the only part left.
I have not seen a shorted tantalum before where it could not be surge current related until now. On Sat, 24 Mar 2012 00:08:12 -0400, Peter Gottlieb <n...@verizon.net> wrote: >I had a HP 3326 which had a power supply in foldback. All the modules are >inaccessible unless you have a rather rare set of extenders anyway. The >voltmeter method quickly led me to the board and a bench supply and meter >again to the shorted cap. Very easy. Other times I've borrowed the FLIR camera >from work, also taught the new EEs that trick as well. It is a true lifesaver >on dense surface mount boards. I haven't tried the liquid crystal sheet but it >seems like an interesting idea so long as everything is about the same height. > > >Peter > >On Mar 23, 2012, at 11:53 PM, li...@lazygranch.com wrote: > >> Prior to emission or IR microscope technology, liquid crystals was how you >> found hotspots on ICs. I've done this with a goop that you dispense with a >> syringe. >> >> One trick to make this more sensitive is you bring a soldering iron close to >> the liquid crystals. Not so close as to cause a change, but you get them >> closer to the phase change point. >> >> >> -----Original Message----- >> From: Skip Withrow <skip.with...@gmail.com> >> Sender: time-nuts-boun...@febo.com >> Date: Fri, 23 Mar 2012 21:07:45 >> To: <time-nuts@febo.com> >> Reply-To: swith...@alum.mit.edu, >> Discussion of precise time and frequency measurement >> <time-nuts@febo.com> >> Subject: [time-nuts] Anyone familiar with SR-620 repair? >> >> You don't need expensive test equipment to find this kind of problem. What >> I use is a sheet of liquid crystal film with a transition temperature just >> slightly above your room temperature. Just lay it on the circuit board and >> you can find where the power is being dissipated (even if pretty small) by >> watching the colors change. >> >> I think Omega Engineering sells a 8.5" x 11" sheet for about $18 if memory >> serves me. I have used this trick many times and it works great to find >> shorted (bypass) caps. No disconnecting anything, no milliohm meters, no 4 >> or 5 digit voltmeters. _______________________________________________ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
