Never assume!
I recently stopped into a local hardware/feed store looking for an X-acto knife to use as a pin vise to hold a sewing needle to clear circuit board holes. When I explained what I was looking for, one of the owners showed me the PSU board to his Mitsubishi TV that had been damaged by a storm. One of the primary Nichicons was bulged, so he'd removed it and two of the other primary caps from the unit but said that he couldn't find replacements anywhere. I explained to him how to find good replacements on Digi-Key or Mouser, but he asked me to get them for him and put them in. I'm not looking for another career as a repair tech, though it's fun to fix things and solve the puzzles involved, but to be helpful I agreed to put the capacitors in.
When I got the board back to work, I got ready to take the two remaining primary caps out. We'd been handling this board and he had already taken out two 1000 uF 200 V Nichicons and a 150 uF 450 V Jamicon, so I had assumed that he had discharged the caps.
Also, he said that he had taken the board out of the TV more than a month ago. Fortunately, my early electronics training came back to me and I thought that I should short the remaining primary caps to follow proper procedures. One of the 1000 uF 200V Nichicons was live! It made a huge spark and a loud snap. The unit's owner was lucky. He said that he didn't discharge the caps that he took out before unsoldering them. 
I don't know if the repair was successful yet; the owner said that it was fairly involved take the TV apart to get to the PSU. I explained that there could be more than damaged caps and that other damage could cause the new caps to explode when the unit was powered up, or worse. The owner said that he read online that storm damage on this TV was usually damaged primary caps and that the unit still partially worked before he pulled the PSU, so he felt that the chances were good that it was just the caps.
When I got the board back to work, I got ready to take the two remaining primary caps out. We'd been handling this board and he had already taken out two 1000 uF 200 V Nichicons and a 150 uF 450 V Jamicon, so I had assumed that he had discharged the caps.
Also, he said that he had taken the board out of the TV more than a month ago. Fortunately, my early electronics training came back to me and I thought that I should short the remaining primary caps to follow proper procedures. One of the 1000 uF 200V Nichicons was live! It made a huge spark and a loud snap. The unit's owner was lucky. He said that he didn't discharge the caps that he took out before unsoldering them. I don't know if the repair was successful yet; the owner said that it was fairly involved take the TV apart to get to the PSU. I explained that there could be more than damaged caps and that other damage could cause the new caps to explode when the unit was powered up, or worse. The owner said that he read online that storm damage on this TV was usually damaged primary caps and that the unit still partially worked before he pulled the PSU, so he felt that the chances were good that it was just the caps.
Comment