Gene Pink
Well-known member
This DIY circuit might have been from the '70s or 80's, likely in Popular Electronics. The general idea was to follow currents flowing in circuit board traces by the microvolts drop, using a voltage controlled oscillator and a speaker to indicate what was going on without taking your eyes off the work, very handy
In use, you might set a pot for a 1K tone, and perhaps connect one probe to where the (+) power supply wire enters the board under test, and work your way down the (+) rail with the other probe, hearing the tone change, perhaps a full note per inch of trace if there was heavy current, as it was very sensitive. You go past a fork in the road, tone stops changing, take the other fork and the tone continues changing. That's where all the current is going. Go past a solder pod and the tone stops changing, and there ya go, the current hog.
20+ years ago, I breadboarded this, used it several times as-is on repairs, and set it aside to build properly "when I had the time". Sound familiar? Found the breadboard yesterday but things are missing.
The front end, and the concept, are similar to the schematic attached, but the resistor values are substantially different (1 ohm between probes), and there is a 4558, 2n3904 and 2n3906, the transistors are likely to drive the speaker, not really enough left of it to tell.
Does any of this seem familiar to anyone? I'd love to find the original schematic of this DIY build, and build it up proper. It worked well with power amps, along with a variac set really low, on an amp that had more than the usual blown output device problems.
I hope this post was lucid, my eyes are bugged out from 5 hours of searching Popular Electronic PDF archives, crappily rendered in Adobe.
Thanks,
Gene
In use, you might set a pot for a 1K tone, and perhaps connect one probe to where the (+) power supply wire enters the board under test, and work your way down the (+) rail with the other probe, hearing the tone change, perhaps a full note per inch of trace if there was heavy current, as it was very sensitive. You go past a fork in the road, tone stops changing, take the other fork and the tone continues changing. That's where all the current is going. Go past a solder pod and the tone stops changing, and there ya go, the current hog.
20+ years ago, I breadboarded this, used it several times as-is on repairs, and set it aside to build properly "when I had the time". Sound familiar? Found the breadboard yesterday but things are missing.
The front end, and the concept, are similar to the schematic attached, but the resistor values are substantially different (1 ohm between probes), and there is a 4558, 2n3904 and 2n3906, the transistors are likely to drive the speaker, not really enough left of it to tell.
Does any of this seem familiar to anyone? I'd love to find the original schematic of this DIY build, and build it up proper. It worked well with power amps, along with a variac set really low, on an amp that had more than the usual blown output device problems.
I hope this post was lucid, my eyes are bugged out from 5 hours of searching Popular Electronic PDF archives, crappily rendered in Adobe.
Thanks,
Gene