Re: Samsung ln46c630, bn44-00341b, j852
High voltages, resistors and such - its going to hurt someone sooner than later.
I cringe everytime I see those 8 pin switches (7 with a missing pin) with such minimal gaps between the legs. Sometimes on the same P/S boards where the manufacturer has put cuts in the board to help separate the legs of mosfets dealing with the same voltages. I know the gap at the mosfet end is close as well, but the pot material seems very stable, I reckon a fair number are killed by the dust that catches between the legs.
Lately I have seen far more boards now with mosfets using sleeved legs to stop dust arc overs destroying them.
Many 2009 -2011 fluro tube LG 42 and 47inch LCDs used black and clear sleeving to help separate the high voltage drive cables from the metal work. The clear seems fine, but almost all of the black sleeving around here is disintegrating leaving what looks like 1kv low frequency cables dealing with 1500v high frequency drive voltages, many which pass through the back and run along the fluro side metal. We have a chocolate called flake here and that's what it looks like as it breaks up.
LG 42 inch LCDs with the big hole in the front (scarlet red, forget the model) had no clearance from the bottom of the power supply and the metal case, pins from the transformers slowly ate their way through the plastic protection material (speaker vibration) causing the P/S board to burn.
Resistors have four ratings to worry about with high voltages. First is the power rating, which for high impedance voltage measurements shouldn't be an issue. Second is the internal wire to wire separation gap either side of the resistant filler with the pot material coating. Third is the pin to pin gap for arc breakdowns on the board itself (including point corners on the pad, electrons love jumping off points). And finally, the resistance of the pot material to hang onto moisture and dust particles on the outside causing corona issues and flashovers.
I'd be suggesting all resistors dealing with more than 100v should be broken into resistor strings for peace of mind. I used to do design work in the HV/HC industry.
High voltages, resistors and such - its going to hurt someone sooner than later.
I cringe everytime I see those 8 pin switches (7 with a missing pin) with such minimal gaps between the legs. Sometimes on the same P/S boards where the manufacturer has put cuts in the board to help separate the legs of mosfets dealing with the same voltages. I know the gap at the mosfet end is close as well, but the pot material seems very stable, I reckon a fair number are killed by the dust that catches between the legs.
Lately I have seen far more boards now with mosfets using sleeved legs to stop dust arc overs destroying them.
Many 2009 -2011 fluro tube LG 42 and 47inch LCDs used black and clear sleeving to help separate the high voltage drive cables from the metal work. The clear seems fine, but almost all of the black sleeving around here is disintegrating leaving what looks like 1kv low frequency cables dealing with 1500v high frequency drive voltages, many which pass through the back and run along the fluro side metal. We have a chocolate called flake here and that's what it looks like as it breaks up.
LG 42 inch LCDs with the big hole in the front (scarlet red, forget the model) had no clearance from the bottom of the power supply and the metal case, pins from the transformers slowly ate their way through the plastic protection material (speaker vibration) causing the P/S board to burn.
Resistors have four ratings to worry about with high voltages. First is the power rating, which for high impedance voltage measurements shouldn't be an issue. Second is the internal wire to wire separation gap either side of the resistant filler with the pot material coating. Third is the pin to pin gap for arc breakdowns on the board itself (including point corners on the pad, electrons love jumping off points). And finally, the resistance of the pot material to hang onto moisture and dust particles on the outside causing corona issues and flashovers.
I'd be suggesting all resistors dealing with more than 100v should be broken into resistor strings for peace of mind. I used to do design work in the HV/HC industry.
Comment