Samsung Syncmaster 931BW - No Power

[Glennjamin]

Re: Samsung Syncmaster 931BW - No Power

The full part number is FSDM0465RB. Many times it is abbreviated to the numbers on the IC, DM0465R. There are several auctions in Great Britain. This auction also looks good, you get two, but shipping could take a while; I'm not sure about import duties. There are also several higher current variations, I don't think it is worthwhile to upgrade.

PlainBill

Hello again!

I return having received my FPS and successfully replaced it on my powerboard. In doing so I rebuilt the monitor and turned it on...nothing again, no LED light around the power button.

I took it apart once again and did the test you recommended before on the output connector - originally showing no values. I now get values of about 13-14V on the 15V connector and about 5V on the 5.1V connector. So the powerboard seems to be back to life but the monitor isn't. Any ideas?

[jetadm123]

Re: Samsung Syncmaster 931BW - No Power

Hello again!

I return having received my FPS and successfully replaced it on my powerboard. In doing so I rebuilt the monitor and turned it on...nothing again, no LED light around the power button.

I took it apart once again and did the test you recommended before on the output connector - originally showing no values. I now get values of about 13-14V on the 15V connector and about 5V on the 5.1V connector. So the powerboard seems to be back to life but the monitor isn't. Any ideas?

Good job on getting the power back up and running. Since you're not even getting the power light, it would seem that you will now need to concentrate on the logic board. This is the board at the other end of the wiring harness from the power board. Please post some good photos of the entire logic board.

[Glennjamin]

Re: Samsung Syncmaster 931BW - No Power

Thanks, it feels like some progress at least! I will do so in the morning when I have good natural light, I did already post one image which isn't too clear back on post #14 - https://www.badcaps.net/forum/showpo...9&postcount=14

Probably not too much you can gain from that but it does seem a fairly unexciting logic board.

[Glennjamin]

Re: Samsung Syncmaster 931BW - No Power

Logic board pictures -

1. Full front
2. Full back
3 & 4. Close halves of front
5 & 6. Close halves of back

[jetadm123]

Re: Samsung Syncmaster 931BW - No Power

At this point, I would suggest measuring the output of the voltage regulators circled in yellow. Measure and report voltage at each leg and metal tab (at the top of each regulator). Also, please include the part number off of each regulator.

[Glennjamin]

Re: Samsung Syncmaster 931BW - No Power

How would do that with my DMM, I'm still quite the novice 25 posts later this thread sorry! On 20VDC and the black & red probe on which points exactly? Thanks.

[jetadm123]

Re: Samsung Syncmaster 931BW - No Power

20VDC setting is good. Neg (black) probe on one of the screws holding down the logic board. Pos (red) probe on each leg and tab as requested.

[Glennjamin]

Re: Samsung Syncmaster 931BW - No Power

Thanks for clarifying, I've attached a picture illustrating the values of the two regulators and their part numbers above each.

[jetadm123]

Re: Samsung Syncmaster 931BW - No Power

The outputs look good for both regulators. The input voltage for the right side regulator seems a bit odd at 3.8V. Not sure if there's a short somewhere dragging down that voltage. Try measuring the input voltage of the right side regulator again. This time place the neg probe on the left leg and the red probe on the right leg.

[Glennjamin]

Re: Samsung Syncmaster 931BW - No Power

OK doing that is still giving me a very consistent 3.8V with absolutely no fluctuation. Do you know what the output voltage should be for the connector to the front power button? I'm not sure if that is important in this case though.

[PlainBill]

Re: Samsung Syncmaster 931BW - No Power

OK doing that is still giving me a very consistent 3.8V with absolutely no fluctuation. Do you know what the output voltage should be for the connector to the front power button? I'm not sure if that is important in this case though.

The connector appears to have 4 pins. If that is the case, one should be 0 volts, another either 3.3 or 5V, and the voltage on one will vary, depending on which button is pressed. The last will control the front LED.

PlainBill

[Glennjamin]

Re: Samsung Syncmaster 931BW - No Power

Hi again, I've been away for a week and unable to test. Update.

The connector appears to have 4 pins. If that is the case, one should be 0 volts, another either 3.3 or 5V, and the voltage on one will vary, depending on which button is pressed. The last will control the front LED.

PlainBill

The output connector on the logic board does indeed have 4 pins and they test the following values:

Pin 1: 0 V
Pin 2: 1.8 V
Pin 3: 1.8 V
Pin 4: 2.1 V

I also own a Samsung 226BW which I pulled apart and borrowed the switch and connecting cable (which are the same). No surprises, no change...so the switch and cable are fine.

The two 1.8 readings shouldn't be that low should they?

[PlainBill]

Re: Samsung Syncmaster 931BW - No Power

Hi again, I've been away for a week and unable to test. Update.

The output connector on the logic board does indeed have 4 pins and they test the following values:

Pin 1: 0 V
Pin 2: 1.8 V
Pin 3: 1.8 V
Pin 4: 2.1 V

I also own a Samsung 226BW which I pulled apart and borrowed the switch and connecting cable (which are the same). No surprises, no change...so the switch and cable are fine.

The two 1.8 readings shouldn't be that low should they?

Unusual, but not unknown. There are three general designs for wiring the switches on a control panel.

One is very simple - each button is connected by a wire to an input of the processor. Pushing a button pulls that line low. For 5 buttons that requires 6 wires plus whatever is required for the LED.

The next is a little more complex. The switches will be wired in a grid, each button will connect a drive line to a sense line. For 5 buttons that requires 5 wires, plus whatever is required for the LED.

The latest version uses two wires, a sense line tied to a voltage source, and a ground line. One side of each button is tied to ground, the other is tied to the sense line through a unique value resistor. By measuring the voltage on the sense line, it is possible to determine which button (or even a combination of buttons) has been pressed.

PlainBill

[renard-ad]

Re: Samsung Syncmaster 931BW - No Power

Dear all,

I did a complete recap (except main 450V cap) and the symptoms remains the same.

As before, the backlight functions one second and then shuts down. It never switch on again (unless I push on / off button). So there is no retry after a timer.

Have you got any idea of what it could be ?

Thanks,

renArD
PS : Let me just correct something I said : there are no 30V bursts on the 15V line, it is my voltmeter failure (curious).

[PlainBill]

Re: Samsung Syncmaster 931BW - No Power

Dear all,

I did a complete recap (except main 450V cap) and the symptoms remains the same.

As before, the backlight functions one second and then shuts down. It never switch on again (unless I push on / off button). So there is no retry after a timer.

Have you got any idea of what it could be ?

Thanks,

renArD
PS : Let me just correct something I said : there are no 30V bursts on the 15V line, it is my voltmeter failure (curious).

I've marked up the picture you supplied of the power supply bottom. Note there are two pins circled in orange, and two circled in yellow.

Set your DMM on the 2000 (2K) Ohms range. Measure the resistance between the pins circle in orange. Report that. Measure the resistance between the two points circled in yellow. Report that. If the two numbers match to within 3%, the transformer is probably good.

PlainBill

[Panther]

Re: Samsung Syncmaster 931BW - No Power

I don't know if this will be of any help, but I recently repaired a Samsung 940N with the same board (from memory) as that shown by renard-ad.

In my case the fault was caused by the inverter transformer. It's resistance between the two outputs was quite different. It was causing one CCFL to be very dim for the second or two before it shut down.

I bought a replacement transformer on eBay from this shop.

http://cgi.ebay.com.au/ws/eBayISAPI....m=350472418043

Good luck.

[renard-ad]

Re: Samsung Syncmaster 931BW - No Power

Thanks to both of you for your quick replies. It makes me eager to try / measure ! (unfortunately I work in a city I don't come from. I'll check as soon as possible : next week end).

The link to ebay doesn't work due to country legal restrictions. I guess you meant this : http://cgi.ebay.fr/TMS92515CT-Invert...item2309d5fbeb

As I was doing some research about this transformer, I saw it is quite "famous", so it may confirm it is the faulty part. Maybe the zzzz noise comes from it too. I can't wait next week-end

[PlainBill]

Re: Samsung Syncmaster 931BW - No Power

I don't know if this will be of any help, but I recently repaired a Samsung 940N with the same board (from memory) as that shown by renard-ad.

In my case the fault was caused by the inverter transformer. It's resistance between the two outputs was quite different. It was causing one CCFL to be very dim for the second or two before it shut down.

I bought a replacement transformer on eBay from this shop.

http://cgi.ebay.com.au/ws/eBayISAPI....m=350472418043

Good luck.

One of the fallacies beginners fall into is 'This fixed John's monitor, so it will fix mine, even though the problem is different.' A second is 'This fixed Joe's monitor and the symptoms are the same, so it will fix mine.' Neither are true.

Looking at troubleshooting reports, failure of a transformer is the third most likely cause of 'two seconds to black'. It is also the easiest to test. Blindly replacing a transformer is foolish. Ignoring the possibility that a transformer is the cause is equally foolish.

PlainBill

[Panther]

Re: Samsung Syncmaster 931BW - No Power

One of the fallacies beginners fall into is 'This fixed John's monitor, so it will fix mine, even though the problem is different.' A second is 'This fixed Joe's monitor and the symptoms are the same, so it will fix mine.' Neither are true.

Blindly replacing a transformer is foolish. Ignoring the possibility that a transformer is the cause is equally foolish.

PlainBill

As I stated quite clearly (or so I thought), a faulty transformer was found to be the cause in my case. Never did I say it's going to be the cause of the problem with other monitors.
Futhermore, I also stated the resistance readings from each secondary were quite different therefore indicating a transformer fault, so I didn't replace it blindly nor did I suggest that anyone should do so.

I was just pointing out that a faulty transformer is a legitimate cause of these symptoms with this model of monitor and therefore worth checking. Then if found to be suspect a replacement is easy to obtain on eBay.

[renard-ad]

Re: Samsung Syncmaster 931BW - No Power

Hello, I'm back with the measures

According to the circles made by Plainbill, I name from "a" at the top left, to "d" at the top right pin. I'm sorry, I can't tell colours apart (I'm partly colour blind). I guess yellows on the left (Rab), and orange on the right (Rcd).

Rab = 3.197k Ohm
Rbc = 221,2k Ohm (parallel to the also noted "R31" on the board)
Rcd = 1.136k Ohm
I could also unsold the transformer if needed.

Obviously, values don't match in the 3% range. So I guess the transformer is bad. I let your wise confirm it !

If you could also explain me why the resistance can change (I would say it is either good or open circuit), I'm also interested in that

Thanks,

renArD