Broken board trying to measure it

Thread Starter

looper

Joined Jan 27, 2013
6
Hello,

I got an energy meter board broken trying to measure it. It is bases on BL0930E chip and I connected the oscilloscope to CF and GND points but it burned out as you can see attached. Any idea what I made wrong?

Regards
 

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wayneh

Joined Sep 9, 2010
16,251
Thanks, but what I don't know is what happened, what was wrong in order to no repeat it
You either caused a short by touching more than one point on the board with a single probe, or - as described in the provided link - your probes were not isolated from the board and you introduced a current path the instant you touched the probe to the board.
 

BBee

Joined Dec 6, 2018
35
Looking at the chip U3 it looks like it has shorted out pins on the left hand side. After a close look I would suggest using iso-propyl alcohol to clean the burnt area for a closer look. Take a good look at all connections, especially for short circuits.

On further look the chip pins may all go to ground so the previous advice about the isolated probe may be the thing. Don't forget a scope earth is usually at ground potential which can differ from the circuit ground.

Tracy
 
Last edited:

LesJones

Joined Jan 8, 2017
2,502
I think it is a non isolated power supply. I think the input bridge rectifier will be connectet straight across the mains via a a capacitor. (My guess is that the capacitor will be about 0.47 uF and at least 250 volts AC rating. By connecting your oscilloscope ground lead to it you will have probably applied the mains voltage directly across some of the diodes in the bridge rectifier. I have just noticed that Tracy's last sentence suggests the same cause. I do not think it will be woth trying to repair it after such severe damage.

Les.
 

Thread Starter

looper

Joined Jan 27, 2013
6
I think it is a non isolated power supply. I think the input bridge rectifier will be connectet straight across the mains via a a capacitor. (My guess is that the capacitor will be about 0.47 uF and at least 250 volts AC rating. By connecting your oscilloscope ground lead to it you will have probably applied the mains voltage directly across some of the diodes in the bridge rectifier. I have just noticed that Tracy's last sentence suggests the same cause. I do not think it will be woth trying to repair it after such severe damage.

Les.
I think I need further experience on using the oscilloscope. May CF point have a 220ac? It is a DC chip working at 5v
 
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