I have 4 of these SyncMaster 940Ts that all came to me with the same problem - no power. I opened them up and found that the 3 820uF 25v caps were bulging, so I replaced them. The power supply still whines, and I'm not sure why. I added a little fresh solder to many joints (transformers, caps, inductors, etc.) but that didn't help.
I also found that the inverter fuse (3A pico-fuse) was blown. I replaced it and the monitor worked for about 30 seconds, then the backlight went out (fuse blew). I tried again with a glass fuse attached to posts soldered in the back of the board where the fuse goes, and watched that fuse blow too. I hooked my multimeter in series and watched current through the inverter, and was surprised to find that the current increases exponentially after the power is switched on - it's very slow at first (starting around 2A), but it increases at an increasing rate. When it gets to about 2.6A, it really takes off and the fuse blows (something also starts hissing around this time). Any thoughts on what might be going on here? It seems like this is related to the temperature of some component as starting current is higher if I switch the monitor off then back on than it is if I leave the monitor off for a few minutes and then turn it on.
I watched the 13v output from the power supply with my scope, and that thing has a terrible ripple to it - I think it's around 5v once the inverter turns on, but I have no idea if this is normal. I was considering running the inverter off my adjustable regulated power supply by applying power where the fuse goes, but wasn't sure if that would be safe.
I gave the CCFLs I'm testing with a quick check using my case mod kit inverter, and current through that inverter is about the same on the 4 lamps (about 10-20mA higher on the top two than the bottom two, but it doesn't seem to me like this would cause the inverter to go out of control).
I also had problems picking replacement caps for this monitor. I used either 3 1000uF 25v Nichicon VZ or 3 1000uF 25v Panasonic NHG as they were all I had that would fit; the originals are 10mmx20mm, and I haven't been able to find a good source for caps that would fit. I see that Panasonic has a new FR series that looks promising, but nobody I've found has the caps I need in stock. The 3 820uF 25v caps are in parallel, so I could do 2 1000uF + 1 470uF or something like that; I might also be able to get away with a 12.5mmx20mm cap in one position and skip either one or both of the others (if I can find a 12.5mmx20mm 2200uF 25v cap, for example, or maybe 1 1800uF + 1 680uF). I read through a few other threads on this topic, but didn't find an answer that I felt would work for me as most of the good quality 1000uF 25v caps are either 12.5mm diameter, 25mm tall, or out of stock, and I don't think I can fit those parts on this IP board. I'd appreciate any thoughts on this problem, unless the Nichicon VZs or Panasonic NHGs are good enough to leave in the board (I don't think so, but thought I'd check).
For reference, I found a schematic at elektrotanya.com (though I'm not 100% sure it's the right one as it covers a range of models) and I read the inverter IC (U201) as a BIT3195G (which I cannot find a datasheet for).
I also found that the inverter fuse (3A pico-fuse) was blown. I replaced it and the monitor worked for about 30 seconds, then the backlight went out (fuse blew). I tried again with a glass fuse attached to posts soldered in the back of the board where the fuse goes, and watched that fuse blow too. I hooked my multimeter in series and watched current through the inverter, and was surprised to find that the current increases exponentially after the power is switched on - it's very slow at first (starting around 2A), but it increases at an increasing rate. When it gets to about 2.6A, it really takes off and the fuse blows (something also starts hissing around this time). Any thoughts on what might be going on here? It seems like this is related to the temperature of some component as starting current is higher if I switch the monitor off then back on than it is if I leave the monitor off for a few minutes and then turn it on.
I watched the 13v output from the power supply with my scope, and that thing has a terrible ripple to it - I think it's around 5v once the inverter turns on, but I have no idea if this is normal. I was considering running the inverter off my adjustable regulated power supply by applying power where the fuse goes, but wasn't sure if that would be safe.
I gave the CCFLs I'm testing with a quick check using my case mod kit inverter, and current through that inverter is about the same on the 4 lamps (about 10-20mA higher on the top two than the bottom two, but it doesn't seem to me like this would cause the inverter to go out of control).
I also had problems picking replacement caps for this monitor. I used either 3 1000uF 25v Nichicon VZ or 3 1000uF 25v Panasonic NHG as they were all I had that would fit; the originals are 10mmx20mm, and I haven't been able to find a good source for caps that would fit. I see that Panasonic has a new FR series that looks promising, but nobody I've found has the caps I need in stock. The 3 820uF 25v caps are in parallel, so I could do 2 1000uF + 1 470uF or something like that; I might also be able to get away with a 12.5mmx20mm cap in one position and skip either one or both of the others (if I can find a 12.5mmx20mm 2200uF 25v cap, for example, or maybe 1 1800uF + 1 680uF). I read through a few other threads on this topic, but didn't find an answer that I felt would work for me as most of the good quality 1000uF 25v caps are either 12.5mm diameter, 25mm tall, or out of stock, and I don't think I can fit those parts on this IP board. I'd appreciate any thoughts on this problem, unless the Nichicon VZs or Panasonic NHGs are good enough to leave in the board (I don't think so, but thought I'd check).
For reference, I found a schematic at elektrotanya.com (though I'm not 100% sure it's the right one as it covers a range of models) and I read the inverter IC (U201) as a BIT3195G (which I cannot find a datasheet for).
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