Benq FP557s monitor not turning on (bad DS-1107a supply)
Good day folks. So I've got this Benq monitor I'm trying to fix (for no reason really, since it's a piece of sh!t), but I can't really put my finger on what's wrong with its power supply DS-1107a - I'll explain. What annoys me the most is that this is one of the worst supplies I've ever worked on: the design itself is horrendous - there's no clear separation between primary and secondary - it doesn't just go left to right or top to bottom...everything just runs all over the place, making the job of tracing what goes where very slow and difficult ! The connector for the main board is not even labeled, so I don't even know what those pins do (though I'm slowly starting to piece it together). Benq also decided to use some of the most obscure parts on the planet, many of which I can't even find a datasheet for. There's no schematic for this PSU, of course, so the odds are really stacked against me. Could this possibly get any worse ? 
The PSU sort-of works: I do get some volts on the secondary, namely 14v where that TO-220 diode is on the right and also 3.5 v out of that single diode (where another TO-220 should go. Lower middle-right). Those 3v show up somewhere on that connector CN701 (presumably the STBY voltage), but that's about it - no other voltages on that connector. I should see at least 12-14v on pins 11 and 12 on the far right. Not having a schematic on hand, I'm not entirely sure to which pin I should apply those 3v to fire up the supply, though I have a vague idea.
Another thing I noticed is that fuse I took a close-up of (PF751 with BEL MS 2A written on it)...what is this thing ? Is it a normal 2a fuse, or is it something more "fancy" ? I'm asking because its behavior is weird: I don't get continuity across it, which made me think it's blown, but upon applying power to the board, 14v go on one side of the fuse and instead of the other side being dead, it slowly rises until it eventually reaches 14v :| Now that I think of it, there's probably some other component (presumably a capacitor) which connects the two sides of the fuse together, but if that's indeed the case, then that fuse blew for a reason. Probing for shorts, I could not find any, but people have suggested that some of those transistors can go bad, so can they indeed do so without becoming shorted ? Has anyone tried anything else ? Lemme know if you need better shots of other parts of the board - it's such a mess of parts going on that it might be difficult to track something. Cheers
The PSU sort-of works: I do get some volts on the secondary, namely 14v where that TO-220 diode is on the right and also 3.5 v out of that single diode (where another TO-220 should go. Lower middle-right). Those 3v show up somewhere on that connector CN701 (presumably the STBY voltage), but that's about it - no other voltages on that connector. I should see at least 12-14v on pins 11 and 12 on the far right. Not having a schematic on hand, I'm not entirely sure to which pin I should apply those 3v to fire up the supply, though I have a vague idea.
Another thing I noticed is that fuse I took a close-up of (PF751 with BEL MS 2A written on it)...what is this thing ? Is it a normal 2a fuse, or is it something more "fancy" ? I'm asking because its behavior is weird: I don't get continuity across it, which made me think it's blown, but upon applying power to the board, 14v go on one side of the fuse and instead of the other side being dead, it slowly rises until it eventually reaches 14v :| Now that I think of it, there's probably some other component (presumably a capacitor) which connects the two sides of the fuse together, but if that's indeed the case, then that fuse blew for a reason. Probing for shorts, I could not find any, but people have suggested that some of those transistors can go bad, so can they indeed do so without becoming shorted ? Has anyone tried anything else ? Lemme know if you need better shots of other parts of the board - it's such a mess of parts going on that it might be difficult to track something. Cheers
Attached Files
Apparently it blew for no reason :|
I picked it up last November from someone on my local Craigslist. It wasn’t very close to where I live, but was close to a family friend that I had to go visit anyways. So after watching the posting on Craigslist for a few weeks and seeing it getting...
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