Samsung SyncMaster 940T blows inverter fuse

[stevenps]

Re: Samsung SyncMaster 940T blows inverter fuse

I hope when you get the correct caps fitted, this solves your 'blowing fuse' problem,however I am not convinced that it will !! so looking forward with interest to the outcome.

I hope so too. Since nobody had any better suggestions given the physical constraints on this board, I went ahead and ordered two monitors' worth of Nichicon HE 1000uF 10v and 680uF 25v. I put in a backorder for the Panasonic FK 820uF 25v from Newark, which claimed a 40 day lead time so I may see them sometime this year. I'll happily use better/different caps on the other two monitors, once I figure out why they're misbehaving. I will report what happens when I get my replacement caps in.

[Rtech]

Re: Samsung SyncMaster 940T blows inverter fuse

I hope when you get the correct caps fitted, this solves your 'blowing fuse' problem,however I am not convinced that it will !! so looking forward with interest to the outcome.

[stevenps]

Re: Samsung SyncMaster 940T blows inverter fuse

Yes, those 25v 820uF CapXon GL caps do indeed have a very odd size. Not long ago I had to replace two of them in a SyncMaster 931B. The closest replacement I could find at Mouser was 25v, 1000uF United Chemicon KY in a 12.5mm x 20mm size. They were a bit of a tight fit, but it worked. I see that Digikey has a few more choices, though.

Question - how much height do you have available before the caps hit the PSU cover? If just a bit more than 25mm, then there's quite a few choices at Digikey:
United Chemicon KY, 10x25: 565-1553-ND
United Chemicon KZE, 10x25: 565-1680-ND
Panasonic FM, 10x25: P12391-ND
Nichicon HE, 10x25: 493-1556-ND
Nichicon PW, 10x25: 493-1830-ND

For the 10v, 1000uF CapXon KM:
Panasonic FC, 10x20: P10225-ND
Panasonic FM, 10x16: P12353-ND
Nichicon HE, 10x16: 493-1497-ND
Nichicon PW, 10x16: 493-1746-ND

As far as United Chemicon goes, they are actually very reliable caps. They only have problems with their KZG and KZJ series.

A 25mm cap hits the case and pushes the board up a little bit. I used Panasonic FC caps (10x25) in a similar monitor once, using washers to space the board up a little bit. I really didn't like that, as the screws barely held the board in. I've been using those caps turned sideways in some newer 19" wide screen monitors with no problems, but there's just no clearance in this one. I must use 20mm tall caps, which is most of my problem in finding suitable replacement caps.

[momaka]

Re: Samsung SyncMaster 940T blows inverter fuse

Yes, those 25v 820uF CapXon GL caps do indeed have a very odd size. Not long ago I had to replace two of them in a SyncMaster 931B. The closest replacement I could find at Mouser was 25v, 1000uF United Chemicon KY in a 12.5mm x 20mm size. They were a bit of a tight fit, but it worked. I see that Digikey has a few more choices, though.

Question - how much height do you have available before the caps hit the PSU cover? If just a bit more than 25mm, then there's quite a few choices at Digikey:
United Chemicon KY, 10x25: 565-1553-ND
United Chemicon KZE, 10x25: 565-1680-ND
Panasonic FM, 10x25: P12391-ND
Nichicon HE, 10x25: 493-1556-ND
Nichicon PW, 10x25: 493-1830-ND

For the 10v, 1000uF CapXon KM:
Panasonic FC, 10x20: P10225-ND
Panasonic FM, 10x16: P12353-ND
Nichicon HE, 10x16: 493-1497-ND
Nichicon PW, 10x16: 493-1746-ND

As far as United Chemicon goes, they are actually very reliable caps. They only have problems with their KZG and KZJ series.

[stevenps]

Re: Samsung SyncMaster 940T blows inverter fuse

For CapXon KM use any of the following: United Chemicon LXY, LXZ, KY; Panasonic FC; Nichicon PW, PM, HE; Rubycon YXG
For CapXon GL: United Chemicon KY; Panasonic FK; Nichicon PM, HE; Rubycon PX

I'd be a lot more comfortable with a pair of 1000uF and a 470uF sandwiched in between for the 25 volt caps.

PlainBill

I would like to use exact replacements, but I'm trying to find caps of the brand/series momaka mentioned as suitable and they don't appear to exist.

For the 820uF 25v caps, I can either use 3 of something 10x20, 1 of something 12.5x20 and 1 of something 10x20, or 1 of something as big as 12.5x30 but only if I use 1 cap for the 1000uF 10v instead of 2 (or if I find suitable 8x20 caps; apparently the Rubycon MCZ available here aren't suitable although they would fit).

I was unable to find 10x20 caps in the series mentioned at 820uF 25v or 1000uF 25v; I'm pretty sure I can find something at 470uF 25v. I picked the Nichicon HE 680uF caps because they fit. I looked for something around 1800uF 25v 12.5x20, but couldn't find anything. The only other option that seemed reasonable was a 2200uF 25v 12.5x30 or so, but I couldn't find one of those either.

For the 1000uF 10v caps, I found Nichicon HE 10x16 that would work but only if I use 10x20 caps for the 820s. I could also do the Chemi-Con LXY 1800uF 10v 12.5x20 though I'm not sure about these; I have removed a lot of failed Chemi-Con caps, including some KZJ near the x16 PCIe slot on a motherboard last week.

I'm completely open to suggestions, if you can find caps that fit the physical space available on the board while approximately matching the required ESR and ripple specs and are available from a retailer in the US.

[PlainBill]

Re: Samsung SyncMaster 940T blows inverter fuse

After a lot of shopping around, I think I have a solution. I can use three Nichicon HE 680uF 25v 10mm x 20mm caps (http://search.digikey.com/scripts/Dk...me=493-1554-ND) instead of the 820uF caps (680 is within 20% of 820, and the 3 are in parallel) and one Chemicon LXY 1800uF 25v 12.5mm x 20mm cap (http://search.digikey.com/scripts/Dk...me=565-1758-ND) instead of the 1000uF caps (1800 is within 20% of 2000, and the 2 are in parallel). Does that sound reasonable? I'm having a great deal of trouble finding caps of the series' mentioned in a size that will fit this board.

I'd be a lot more comfortable with a pair of 1000uF and a 470uF sandwiched in between for the 25 volt caps.

PlainBill

[stevenps]

Re: Samsung SyncMaster 940T blows inverter fuse

The ESR of Rubycon MCZ is too low for PSU use, and the ESR of Nichicon VZ and NHG is too high.

For CapXon KM use any of the following: United Chemicon LXY, LXZ, KY; Panasonic FC; Nichicon PW, PM, HE; Rubycon YXG
For CapXon GL: United Chemicon KY; Panasonic FK; Nichicon PM, HE; Rubycon PX
For CapXon KF: United Chemicon KZE; Panasonic FM; Nichicon HD; Rubycon ZL
Most of these are available on Mouser and Digikey. Rubycon ZL, PX, and YXG are available at badcaps.net only.

After a lot of shopping around, I think I have a solution. I can use three Nichicon HE 680uF 25v 10mm x 20mm caps (http://search.digikey.com/scripts/Dk...me=493-1554-ND) instead of the 820uF caps (680 is within 20% of 820, and the 3 are in parallel) and one Chemicon LXY 1800uF 25v 12.5mm x 20mm cap (http://search.digikey.com/scripts/Dk...me=565-1758-ND) instead of the 1000uF caps (1800 is within 20% of 2000, and the 2 are in parallel). Does that sound reasonable? I'm having a great deal of trouble finding caps of the series' mentioned in a size that will fit this board.

[momaka]

Re: Samsung SyncMaster 940T blows inverter fuse

The ESR of Rubycon MCZ is too low for PSU use, and the ESR of Nichicon VZ and NHG is too high.

For CapXon KM use any of the following: United Chemicon LXY, LXZ, KY; Panasonic FC; Nichicon PW, PM, HE; Rubycon YXG
For CapXon GL: United Chemicon KY; Panasonic FK; Nichicon PM, HE; Rubycon PX
For CapXon KF: United Chemicon KZE; Panasonic FM; Nichicon HD; Rubycon ZL
Most of these are available on Mouser and Digikey. Rubycon ZL, PX, and YXG are available at badcaps.net only.

[stevenps]

Re: Samsung SyncMaster 940T blows inverter fuse

Sounds like the Panasonic FK caps would be fine replacements. I'll check around to see if I can find a retailer in the US that stocks these; the only one that comes to mind right away is Newark. I'm not too worried about the 1000uF 10v caps, as I will use Rubycon MCZ for those. For testing purposes, I have some 820uF 25v 10x25 Panasonic FC caps I could solder in though I don't expect simply replacing those caps is going to solve the excessive current draw through the inverter. I'll be extremely happy if I'm wrong though.

Of course, I can't find anyone who wants to sell me these. Newark has them, but is out of stock. I didn't see them at Mouser or Digikey, and eBay wasn't helpful. Any thoughts on where I can get these in the US?

[stevenps]

Re: Samsung SyncMaster 940T blows inverter fuse

My question about testing current flow of the ccfls hooked up to the inverter of your monitor was to see if one particular circuit was drawing an excessive amount of current.
Al.

Ah. I believe I will need to take some time to understand the OCP and OVP circuits on this monitor to properly measure that, unless there's some component I can unsolder and insert my multimeter somewhere. I'll likely need some help doing this, as I have only done this once before, and that was with help from PlainBill.

The datasheet for GL doesn't even list 820uf.
Working on the basis of a 1000uf cap, the ripple should be somewhere around 1530ma, most likely lower for the 820uf, so FK fits fine there.
ESR is about right as well.

1000uf Capxon KM has ripple listed at 550ma and they don't list any specifics for ESR. My opinion is that they're under-rated, I could be wrong.

Sounds like the Panasonic FK caps would be fine replacements. I'll check around to see if I can find a retailer in the US that stocks these; the only one that comes to mind right away is Newark. I'm not too worried about the 1000uF 10v caps, as I will use Rubycon MCZ for those. For testing purposes, I have some 820uF 25v 10x25 Panasonic FC caps I could solder in though I don't expect simply replacing those caps is going to solve the excessive current draw through the inverter. I'll be extremely happy if I'm wrong though.

[seanc]

Re: Samsung SyncMaster 940T blows inverter fuse

The old caps are CapXon GL for the 820uF 25v, and CapXon KM for the 1000uF 10v (I'm using Rubycon MCZ for those, though I think I used Nichicon HZ one time).

The datasheet for GL doesn't even list 820uf.
Working on the basis of a 1000uf cap, the ripple should be somewhere around 1530ma, most likely lower for the 820uf, so FK fits fine there.
ESR is about right as well.

1000uf Capxon KM has ripple listed at 550ma and they don't list any specifics for ESR. My opinion is that they're under-rated, I could be wrong.

[alexanna]

Re: Samsung SyncMaster 940T blows inverter fuse

I didn't test current through the lamps, only through the inverter attached to the lamps. I don't know what a particular reading means on my case mod inverter, so I'm just using it to look for differences in readings between the lamps in the monitor. The top lamps draw slightly more current than the bottom ones do (which should not be a surprise), and each pair has about the same current draw which suggests that I probably don't have a single bad lamp (either both in the pair are bad, or they're both fine). I'm testing basically the same thing for the whole system on the IP board by measuring current through the place where the inverter fuse should be, and I notice that the current increases until it blows the 3A fuse. I'm trying to figure out why that is, and why the power supply whines after I replaced the larger caps (1000uF, 820uF).

My question about testing current flow of the ccfls hooked up to the inverter of your monitor was to see if one particular circuit was drawing an excessive amount of current.
Al.

[stevenps]

Re: Samsung SyncMaster 940T blows inverter fuse

I use Panasonic FK all the time - no problems to report as of yet.
You don't have to use Farnell, I'm sure you can find them elsewhere.

The power supply may well be whining because of the incorrect specification in capacitors, with regards to ESR and ripple.

What brand and series were the old caps?

The old caps are CapXon GL for the 820uF 25v, and CapXon KM for the 1000uF 10v (I'm using Rubycon MCZ for those, though I think I used Nichicon HZ one time).

[seanc]

Re: Samsung SyncMaster 940T blows inverter fuse

I use Panasonic FK all the time - no problems to report as of yet.
You don't have to use Farnell, I'm sure you can find them elsewhere.

The power supply may well be whining because of the incorrect specification in capacitors, with regards to ESR and ripple.

What brand and series were the old caps?

[stevenps]

Re: Samsung SyncMaster 940T blows inverter fuse

I might try measuring the current,without the CCFL's being plugged in !!.That would confirm it is not some weird CCFL fault,and eliminate the current circuits feeding back to the control cct.

Current quickly increases to about 0.12A, sits there for about half a second, then goes back down. I assume this is an indication that the OVP circuit is working.

Panasonic NHG and Nichion VZ aren't good enough in my opinion.

To replace the 820uf 25v, you need Panasonic FK - EEUFK1E821 - http://uk.farnell.com/panasonic/eeuf...0uf/dp/1744941

I remember reading somewhere that someone (PlainBill?) specifically recommended against using these for some reason. Also, I'm in the US and don't really want to pay for Royal Mail to get stuff to me; I think Newark may have those, but I'll wait for someone to confirm the suitability of these caps before I try to order them.

also check AF4502C MOSFETs pins 3 and 4 see if shorted.

Using diode test mode on my multimeter, I see that 3-4 is open one direction and 0.711v in the other direction. I get the same readings on both ICs.

You mention testing current flow of the ccfls with your case mod kit.Have you or can you check the current flow with the ccfls hooked up to your monitor?
Al.

I didn't test current through the lamps, only through the inverter attached to the lamps. I don't know what a particular reading means on my case mod inverter, so I'm just using it to look for differences in readings between the lamps in the monitor. The top lamps draw slightly more current than the bottom ones do (which should not be a surprise), and each pair has about the same current draw which suggests that I probably don't have a single bad lamp (either both in the pair are bad, or they're both fine). I'm testing basically the same thing for the whole system on the IP board by measuring current through the place where the inverter fuse should be, and I notice that the current increases until it blows the 3A fuse. I'm trying to figure out why that is, and why the power supply whines after I replaced the larger caps (1000uF, 820uF).

[alexanna]

Re: Samsung SyncMaster 940T blows inverter fuse

You mention testing current flow of the ccfls with your case mod kit.Have you or can you check the current flow with the ccfls hooked up to your monitor?
Al.

[FIXITNOW]

Re: Samsung SyncMaster 940T blows inverter fuse

also check AF4502C MOSFETs pins 3 and 4 see if shorted.

[seanc]

Re: Samsung SyncMaster 940T blows inverter fuse

Panasonic NHG and Nichion VZ aren't good enough in my opinion.

To replace the 820uf 25v, you need Panasonic FK - EEUFK1E821 - http://uk.farnell.com/panasonic/eeuf...0uf/dp/1744941

[Rtech]

Re: Samsung SyncMaster 940T blows inverter fuse

I might try measuring the current,without the CCFL's being plugged in !!.That would confirm it is not some weird CCFL fault,and eliminate the current circuits feeding back to the control cct.

[stevenps]

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).