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Old 02-15-2013, 02:48 AM   #1
everell
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Default Repairing Bestec TFX0250D5W

Had a Bestec TFX0250D5W come my way. It had several bloated capacitors. So I thought I would try replacing them and see if that fixed it. It didn't fix it! Here are some pictures I took of another Bestec, same model, not as many bloated capacitors. The earlier Bestec that I fixed was a dead 5vsb with bloated C36 capacitor. This one had a handful of bloated capacitors.
Attached Images
File Type: jpg TFX0250D5W 002.jpg (400.8 KB, 90 views)
File Type: jpg TFX0250D5W 003.jpg (464.3 KB, 118 views)
File Type: jpg TFX0250D5W 007.jpg (379.3 KB, 103 views)
File Type: jpg TFX0250D5W 014E.jpg (293.9 KB, 96 views)
File Type: jpg TFX0250D5W 018.jpg (501.5 KB, 98 views)
File Type: jpg TFX0250D5W 019.jpg (400.2 KB, 98 views)
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Old 02-15-2013, 02:50 AM   #2
everell
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Default Re: Repairing Bestec TFX0250D5W

Here are some pictures of the silicon in this psu
Attached Images
File Type: jpg Bestec TFX 2.jpg (226.0 KB, 67 views)
File Type: jpg Bestec TFX 3.jpg (231.5 KB, 60 views)
File Type: jpg Bestec TFX 4.jpg (195.1 KB, 53 views)
File Type: jpg Bestec TFX 5.jpg (206.1 KB, 47 views)
File Type: jpg Bestec TFX 6.jpg (200.6 KB, 45 views)
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Old 02-15-2013, 02:58 AM   #3
everell
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Default Re: Repairing Bestec TFX0250D5W

After replacing the bad caps, the power supply tester LEDs just blinked, the fan just gave a tick. So I measured the output diodes thinking that maybe one was bad. No, they all checked good. So I started tracing the output circuit to see what was in this power supply. To my surprise, there are NO load resistors on the output rails. So I set up a jig with a 12 ohm resistor for the 12 volt rail, a 5 ohm resistor for the 5 volt rail, and a 3.3 ohm resistor for the 3.3 volt rail. The power supply now came up working as expected.

The reason for writing this post..............make sure the power supply you are working on has load resistance on the output rails - or you may be chasing a ghost.

For anyone else working on this particular model Bestec, here are some drawings of the 5vsb circuit and the output circuit. Also a roadmap of the output capacitors. Perhaps this will be helpful to someone.
Attached Files
File Type: pdf Bestec TFX0250D5W 5vsb circuit.pdf (37.8 KB, 141 views)
File Type: pdf Bestec TFX0250 secondary side output.pdf (46.0 KB, 95 views)
File Type: pdf Bestec TFX0250D5W roadmap.pdf (25.8 KB, 106 views)
File Type: pdf Bestec TFX0250 roadmap.pdf (22.9 KB, 73 views)
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Old 02-21-2013, 01:42 AM   #4
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Default Re: Repairing Bestec TFX0250D5W

Nice work everell! Great photos as usual too.

With 17A available on the 12V rail, spec-wise this looks like a really nice 250W PSU.
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Old 06-18-2019, 05:40 AM   #5
Micro System
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Default Re: Repairing Bestec TFX0250D5W

Thanks this images helped in repairing The TNY276PN was burnt and from picture i was able to identify the part no
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