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Electronics Repair (sci.electronics.repair) Discussion of repairing electronic equipment. Topics include requests for assistance, where to obtain servicing information and parts, techniques for diagnosis and repair, and annecdotes about success, failures and problems. |
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Ok, to cut it short, the ac line in goes straight to the primary of
that transformer. That alone energizes the windings to induce the 24 volt standby source which also goes to the relay, as well as the 12,9 and 5 volt lines. When the relay latches, THEN ac is routed to the primary of the swithcing power supply that provides the B+ for the horizontal circuit. Without the smaller standby transformer working, NOTHING else is going to work. To prove or disprove, use an ohm meter and measure resistance on the two secondary pins of that transformer. I got a buck says they're open. Should read shorted or near shorted. There may or may not be a thermal fuse inside the transformer but, the way that's designed, you'll destroy it before you get to it. Best to replace. I finally got around to checking the transformer (after pulling from chassis). There is no standby smaller transformer. Only the big one. Anyhow, I checked the primary windings, and yes, they are open. The secondary is good. After studying the circuit, I agree with your statement above, except about the smaller standby transformer, since it doesn't have one. There is no other transformer on the chassis except for the flyback, which I assume to mean now this is a linear power supply. There is however a (smaller filter transformer? that is first off the main supply), but it's secondary is connected to the "cold" side of the suppy. Nothing connected to the primary. It does check good on primary/secondary. With this said, you have to be right about the primary (big one) supplying the 24V standby voltage, because there is physically no other way for this to be supplied after studying the circuit. Checking the big T in circuit gave inconclusive results because of the filter cap. Again, I'm a beginner. I will follow up post if I repair, based on parts costs. Thanks a million Tech. |
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