4 ms·
It happens I'm a bit familiar with this circuit. I think the author misread the schematic. The burned-out component is more likely the current-sense resistor R2
by avian 8y ago
It happens I'm a bit familiar with this circuit. I think the author misread the schematic. The burned-out component is more likely the current-sense resistor R2 (4.64 ohms).
In any case, it's unlikely that a 1.5 Mohm resistor would burn out like that. Ant or not, you would need a lot higher than line voltage to cause that much power dissipation over 1.5 Mohm.
The combination of two series 1.5 Mohm resistors R3 and R4 is actually well visible in the first photo (two undamaged components with "155" printed on them).
- unwind 8y agoThat's a great find, but given your experience with the circuit, and the different diagnosis, how does that change the likely cause of the problem? Why did the sense resistor get toasty?
- megous 8y agoYou don't need all that much power to toast such a small resistor. Looks like 0805 package, which would be rated for 0.125W max. Easy to burn. It probably burned because of something causing higher current draw than expected by designers. Short or whatvever. If it failed open, which would be expected, it might have acted as a fuse.