Anyone know what D511 is in a '07 Durabrand (Orion)?

[radiotvnut]

OK, I dug around and found an older Orion chassis that used a power supply that appears very close to the one I'm working on. I pulled the diode out of that chassis and stuck it in mine and, of course, it did nothing - that would have been too easy for it to work! After some more checking, I found the fusible resistor between the output of the bridge rectifier and the raw B+ input to the switching transformer to be open. So, back to the junk chassis for a resistor. Installed the resistor and decided to bring the TV up on a variac since we all know what a PITA these switching power supplies can be, as in outputing 10,000 volts where it's only supposed to be 130 V. I monitored the B+; and, with just a few volts AC input - I started out with around 64 volts B+. Then, it started gradually dropping until it got to around 18 volts. I gradually cranked the variac and when I hit about 25 volts AC input, the chopper transistor shorted and it's heatsink was very hot. I have a good transistor in the junk chassis; but, there's no need in changing it until I find out what is causing it to short.

It's situations like this that make me wonder why they couldn't stick with the simple STR30130 based voltage regulator system that was popular during the '80's and '90's? It was a reliable design, the parts count was low, and one didn't have to worry about the power supply running away with itself. About the only trouble one had out of this design was a defective STR30xxx or a resistor in the STR circuit. I guess the engineers sat down one day and said, "The old STR circuit is too easy to repair; so, let's use a switching power supply with discreet components that's much harder to service."