Having a problem with this power supply I think I have narrowed it down to the transformer. When I connect just the primary side it blows the fuse. Removed its ok. Cant find any info on this Chinese Transformer. Is there any chance on repairing this power supply without a schematic or OEM parts?
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Magnavox DRV power supply SMPS
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Re: Magnavox DRV power supply SMPS
Are you sure that the transformer is the main cause..?
if it's true, this is mean disaster.
Because the hardest part to find the replacement is the transformer, except you pull out from the identical board.
Have you already check all component in primary side..?
Try with light bulb trick. not directly from the wall.
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Re: Magnavox DRV power supply SMPS
This is really a puzzler. All of the caps are ok including the polys. Diodes are fine including ones on bottom. The mosfet was bad and I replaced it. I checked the small to92 transistor on the primary side (I assume that controls the mosfet ) and its ok. Xfrm out its ok, primary side connected only it blows. There are 5 connections on the primary xfmr. 2 are connected and the other 3 are. So I was going to put a scope on those connections. I am guessing the signal would be a pseudo AC because its already rectified. Any thoughts?
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Re: Magnavox DRV power supply SMPS
If the power MOSFET that drives the primary winding is stuck fully on instead of switching and off 50~60,000 times a second, that will cause the fuse to blow.
Are you sure that the new MOSFET is not shorted out again?
This is one of those Philips two-Transistor switching power supply, so you have to check ALL the devices in both primary and secondary side really well.
What is the model number of this DVR unit?Never stop learning
Basic LCD TV and Monitor troubleshooting guides.
http://www.badcaps.net/forum/showthr...956#post305956
Voltage Regulator (LDO) testing:
http://www.badcaps.net/forum/showthr...999#post300999
Inverter testing using old CFL:
http://www.badcaps.net/forum/showthr...er+testing+cfl
Tear down pictures : Hit the ">" Show Albums and stories" on the left side
http://s807.photobucket.com/user/budm/library/
TV Factory reset codes listing:
http://www.badcaps.net/forum/showthread.php?t=24809
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Re: Magnavox DRV power supply SMPS
Its a Magnavox mdr557h/F7. Its not that old. Do I have to unsolder the mosfet to really check it correctly. I used a mosfet machine to check it originally but I don't really want to remove it. So what could be taking out the mosfet if its bad. There really are not that many parts on top of the board. There are a bunch of micro components on the bottom that I have not checked. A schematic would be golden.
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Re: Magnavox DRV power supply SMPS
Transformer winding will show very low DC resistance, you need a transformer ringer tester to test it.Never stop learning
Basic LCD TV and Monitor troubleshooting guides.
http://www.badcaps.net/forum/showthr...956#post305956
Voltage Regulator (LDO) testing:
http://www.badcaps.net/forum/showthr...999#post300999
Inverter testing using old CFL:
http://www.badcaps.net/forum/showthr...er+testing+cfl
Tear down pictures : Hit the ">" Show Albums and stories" on the left side
http://s807.photobucket.com/user/budm/library/
TV Factory reset codes listing:
http://www.badcaps.net/forum/showthread.php?t=24809
Comment
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Re: Magnavox DRV power supply SMPS
Originally posted by johnfin View PostWith the transformer removed, should I be able to see the PWM on the primary side with a scope?
Same topology as used in this circuit. PDF.Last edited by budm; 10-24-2017, 09:12 AM.Never stop learning
Basic LCD TV and Monitor troubleshooting guides.
http://www.badcaps.net/forum/showthr...956#post305956
Voltage Regulator (LDO) testing:
http://www.badcaps.net/forum/showthr...999#post300999
Inverter testing using old CFL:
http://www.badcaps.net/forum/showthr...er+testing+cfl
Tear down pictures : Hit the ">" Show Albums and stories" on the left side
http://s807.photobucket.com/user/budm/library/
TV Factory reset codes listing:
http://www.badcaps.net/forum/showthread.php?t=24809
Comment
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Re: Magnavox DRV power supply SMPS
Replace the fuse with a light bulb. It will limit the current, letting you run tests.Things I've fixed: anything from semis to crappy Chinese $2 radios, and now an IoT Dildo....
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Sometimes you need to break shit to fix it.... Thats why my lawnmower doesn't have a deadman switch or engine brake anymore
Follow the white rabbit.
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Re: Magnavox DRV power supply SMPS
Try this schematic, it looks like the same power supply. If the original fet had a short from drain to gate I suspect parts in the drive circuit are damaged.Attached FilesLast edited by R_J; 10-24-2017, 04:05 PM.
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Re: Blown again
Originally posted by johnfin View PostI used the 60watt bulb in place of the fuse and it blew the filament so fast I could not even see it light. Guess I need to use a variac.Never stop learning
Basic LCD TV and Monitor troubleshooting guides.
http://www.badcaps.net/forum/showthr...956#post305956
Voltage Regulator (LDO) testing:
http://www.badcaps.net/forum/showthr...999#post300999
Inverter testing using old CFL:
http://www.badcaps.net/forum/showthr...er+testing+cfl
Tear down pictures : Hit the ">" Show Albums and stories" on the left side
http://s807.photobucket.com/user/budm/library/
TV Factory reset codes listing:
http://www.badcaps.net/forum/showthread.php?t=24809
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