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Old 10-07-2009, 04:30 PM
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Anyone know what D511 is in a '07 Durabrand (Orion)?

I was just given a Durabrand, built by Orion, model DTV1907A from 11/07. I found D511, a zener diode in the power supply to be shorted. I can't find any markings on the diode and I can't find any service information. The cathode terminal connects to the gate terminal of the switching transistor and the anode is connected to hot ground. I know this is just another POC $199 throw away TV; but, I thought I'd at least try to get it going since it has a built in DTV tuner. If I don't get it going, it will be just another dud to have to worry about throwing out. Any help will be appreciated.
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Old 10-07-2009, 07:29 PM
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Their Service Manuals don't include a parts list.

Attached is the service manual for the 13" version of your set - the manuals don't include either a schematic or parts list.

Sorry to be the bearer of bad news.

Cheers,
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Last edited by Findm-Keepm; 07-31-2015 at 02:23 PM.
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Old 10-07-2009, 07:31 PM
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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."
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Old 10-07-2009, 07:31 PM
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....unless you realize it's two manuals.

Here's the parts list and schematic for the 13" version, perhaps it might help.

Cheers,
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Last edited by Findm-Keepm; 09-29-2017 at 06:39 PM.
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Old 10-07-2009, 07:39 PM
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Thank you very much for that information!
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Old 10-08-2009, 07:45 PM
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Quote:
Originally Posted by radiotvnut View Post

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."
Actually, it's the "green" effect - companies seeking the Energy Star or similar "feel good" efficiency ratings for their product. The STR30XXX supplies were linear in nature, wasted energy as heat, and weren't all that reliable. We would see Emerson and similar low-cost sets daily that had the STR blown, leading us to buy them by the "stick" - 50 units at a time, 2 or three times a year. We'd stick a V130 series MOV after the fuse and save the STR's from surges (lightning storms in the southeast...).

But I still hate the danged SMPS design. The military avionics I serviced in the Navy were full of them, for weight saving purposes, and they failed due mostly due to heat. Consumer electronics? No margin for any design deviation - heat, surges, shorts - just about anything and they crap out, not to mention the infamous "let's put underrated electrolytic caps in and see how long this switched-mode supply will last" effect - failure guaranteed 1 hour to 1 day beyond a warranty!

Good luck with your Orion!

Cheers,
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