Re: Ballast Resistors? Source?
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Checking the math and calculating resistor power ratings using the voltages found in the manual: Power (R43) = (265v - 150v)^2 / 6000 ohms = 2.2 watts, which at 5w is a X2 safety margin.? OK Power (R-69) = (265v - 205v)^2 / 1500 ohms = 2.5 watts, which at 5w is a X2 safety margin.? OK Power R-68) = (305v - 265v)^2 / 300 ohms = 5.3 watts, which is not good design work when using a 5w part.?? It seems that R69 should be at least a 10 watt part so that it too has a X2 safety margin! It also looks like the dreaded previous owner left C99 A, B & C in the circuit and poorly tacked soldered the replacement for C99B in parallel with the original filter capacitor.? To add to the problem, the location of the new replacement filter capacitor blocks the radiated heat form the three 5 watt power resistors.? So there is no wonder why R68 and perhaps R69 failed.? I assume that the only remaining good 5 watt resistor is R43 and it still measures close to 6k ohms? Regards, Jim Logic: Method used to arrive at the wrong conclusion, with confidence.? Murphy
On Saturday, January 18, 2025 at 12:52:22 PM CST, Dave Jordan via groups.io <wa3gin@...> wrote:
Amazon, eBay, Mouser On Sat, Jan 18, 2025 at 1:28?PM Richard Oscoda via <upmeharties51=[email protected]> wrote:
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Jim Whartenby