Hey all,
So I'm working on a project using a power supply design I've used many, many times. The supply in question is a simple linear cap input supply regulated to 12V via an LM1085, then split via 2 diodes where one part stays 12V (11.65V), the other is regulated down to 5V. At first power on something didn't feel right and I thought I heard little zaps, but I continued. Voltages measured correct so I then fired up the scope to check for any ripple/oscillations. After hooking the scope probe's ground lead to the supply's ground, I checked the 12V diode's cathode and it would spark from cathode to probe tip.
I immediately shut down and measured the ground connections from supply ground to chassis and scope ground, rechecked the supply for shorts, checked my scope probes for shorts...everything appears OK. I tried testing the circuit again and thought it was resolved but again got sparks after a few times touching that part of the circuit. It seemed as if switching to the 10X setting on the probe made the sparking worse. A second probe did the same thing.
Any clue what could be happening? It seems very odd to me that and arc could occur to a high-impedance scope probe, especially an arc that doesn't seem to damage anything. It's got me a little scared to proceed.
So I'm working on a project using a power supply design I've used many, many times. The supply in question is a simple linear cap input supply regulated to 12V via an LM1085, then split via 2 diodes where one part stays 12V (11.65V), the other is regulated down to 5V. At first power on something didn't feel right and I thought I heard little zaps, but I continued. Voltages measured correct so I then fired up the scope to check for any ripple/oscillations. After hooking the scope probe's ground lead to the supply's ground, I checked the 12V diode's cathode and it would spark from cathode to probe tip.
I immediately shut down and measured the ground connections from supply ground to chassis and scope ground, rechecked the supply for shorts, checked my scope probes for shorts...everything appears OK. I tried testing the circuit again and thought it was resolved but again got sparks after a few times touching that part of the circuit. It seemed as if switching to the 10X setting on the probe made the sparking worse. A second probe did the same thing.
Any clue what could be happening? It seems very odd to me that and arc could occur to a high-impedance scope probe, especially an arc that doesn't seem to damage anything. It's got me a little scared to proceed.