Twin Samsung 931b monitors

[pixel8ed]

I've had these 2 samsung monitors for about 3 or 4 years now. They started having this flickering problem about 18 months into owning them where when I power them up, they would flicker on and off. After powering on and off many times they would finally boot up and stabilize. It's gotten progressively worse until now it takes about an hour for me to power up my monitors. I started researching and found it's a quite common problem and I might be able to fix the problem by replacing the capacitors.

Unfortunately I started the project before finding this very helpful forum. I removed two caps already but hit a snag where my iron wasn't hot enough. So I have a quick question about getting a new iron before I get into posting pics and my other problem now of finding replacement caps.

I read on the FAQ that generally a 60w iron is recommended, but that was geared more toward motherboards. I was using a 9w. I also read that irons tend to put out a charge out of the tip. When I was shopping I saw butane irons and I am wondering if those avoid the problem of static discharge. I don't mind spending a bit on the iron. Should I be shopping for a 60w, butane Iron?

Thanks!

[Kevin O'Henly]

Re: Twin Samsung 931b monitors

Hi,
I would recommend a grounded tip iron (3 prong cord plug) into a ground fault outlet. 60W sounds about right. Get a variety of tips.

I have no experience with butane irons.

Keep a fan blowing any fumes away from your face. I use a fume hood made from an old stove exaust hood. Works well.

If you have been handling led alloy solder then wash the hands before handling food or drink. Do not solder and snack.

Disconnect power and discharge any large capacitors before soldering.

Have fun.

rgs,
Kevin

[pixel8ed]

Re: Twin Samsung 931b monitors

How would you discharge large capacitors?

[pixel8ed]

Re: Twin Samsung 931b monitors

Ok, attached is the board for monitor #1. As far as I can tell, there are 3 caps with a rubbery substance that I'm assuming is leakage. Two others look like they could use replacing. The rest of the photos are the board from different angles. Any thoughts?

[pedro]

Re: Twin Samsung 931b monitors

Ok, attached is the board for monitor #1. As far as I can tell, there are 3 caps with a rubbery substance that I'm assuming is leakage.

Nope, that's an adhesive goo used to provide mechanical support against vibration etc - totally innocent, ignore it. If it is restraining a cap you are trying to replace, just separate it with a thin blade.

Two others look like they could use replacing. The rest of the photos are the board from different angles. Any thoughts?

Certainly two and maybe three are showing signs of failure (bulging tops). Basically replace all the electros except the big one lying down. If there isn't one already, there needs to be a tutorial on the things you need to do:

A. Before ordering replacements:

1. Write down the cap rating (uF and working voltage) of each, together with brand and series (often two letter code).

2. Note the dimensions of each cap (diameter, height). Replacements need to fit, and using the info from 1 alone can lead to a red face later. Pin spacing is pretty much standardised by cap-size nowadays.

3. Someone here will advice which caps to order as replacements, and where from.

4. Ensure you are confident that you have a suitable soldering iron and know how to use it, or enlist the aid of a friend who is/does.

5. Before removing caps, draw a rough sketch of which value was where, and note the polarity. The negative may be marked on the board, but is always the stripe marked "-" down the side of the cap.

B. Once you have the replacments at hand.

6. Check that the replacements will fit (diameter/height).

7. Remove old, install new, snip leads, apply power and behold your working monitor.

Well, that's how it generally goes when failed caps are evident. Sometimes your mileage will vary.

[pedro]

Re: Twin Samsung 931b monitors

Took a decent look at the pics. Three definitely bulging, and yes your board has the polarity marked for you. But you will still need your sketch to record value vs location.

[Kevin O'Henly]

Re: Twin Samsung 931b monitors

I discharge caps using an axial leed 1k ohm resister with insulation on the leads and a blob of solder on the lead ends. Then short the capacitor leads with this resistor, count to 10 and your done.

[almoodie]

Re: Twin Samsung 931b monitors

I have a Samsung 931B with the same problem. Took the power supply board out and wrote down the capacitor values:

2 @ 820 microfarad 25V 105 degrees C
1 @ 470 microfarad 25V 105 degrees C
2 @ 1000 microfarad 10V 105 degrees C
1 @ 330 microfarad 10V 105 degrees C
1 @ 1 microfarad 50V 105 degrees C

then put the monitor back together, I need it for work. Unfortunately I did not know I had to record height, diameter, brand name, etc. Can anybody help me with this info or do I need to take it apart again. Where is the best place to order parts.

Al Moodie.

[PlainBill]

Re: Twin Samsung 931b monitors

I have a Samsung 931B with the same problem. Took the power supply board out and wrote down the capacitor values:

2 @ 820 microfarad 25V 105 degrees C
1 @ 470 microfarad 25V 105 degrees C
2 @ 1000 microfarad 10V 105 degrees C
1 @ 330 microfarad 10V 105 degrees C
1 @ 1 microfarad 50V 105 degrees C

then put the monitor back together, I need it for work. Unfortunately I did not know I had to record height, diameter, brand name, etc. Can anybody help me with this info or do I need to take it apart again. Where is the best place to order parts.

Al Moodie.

You'd better open it up again and make sure. Here are the Digikey part numbers and the Panasonic part numbers for the caps. Note most of them are available in two sizes. Choose First Class mail shipping for low cost and speedy delivery.

2 @ 820 microfarad 25V P11221-ND EEU-FC1E821 2 @ $1.07 OR P11222-ND EEU-FC1E821S 2 @ $1.30

1 @ 470 microfarad 25V P12389-ND EEU-FM1E471L 1 @ $.43 OR P12388-ND EEU-FM1E471 1 @ $.50

2 @ 1000 microfarad 10V P12353-ND EEU-FM1A102 2@ $.50 OR P12354-ND EEU-FM1A102L @ $.50

1 @ 330 microfarad 10V P11184-ND EEUFC1A331 1 @ $.48

1 @ 1 microfarad 50V P10312-ND EEUFC1H1R0 1 @ $.27

PlainBill

[pixel8ed]

Re: Twin Samsung 931b monitors

Here is the photo for monitor #2. Looks like the same 3 are bulging. That should make replacing them easy. I wonder, should I replace all the caps while I'm at it, or just the 3 that appear to be bad?

Next I'm on to ordering the parts. Thanks PlainBill... looks like the parts for both monitors I'm looking for are.

4@ P11221-ND CAP 820UF 25V ELECT FC RADIAL
2@ P12389-ND CAP 470UF 25V ELECT FM RADIAL

[PlainBill]

Re: Twin Samsung 931b monitors

Here is the photo for monitor #2. Looks like the same 3 are bulging. That should make replacing them easy. I wonder, should I replace all the caps while I'm at it, or just the 3 that appear to be bad?

Next I'm on to ordering the parts. Thanks PlainBill... looks like the parts for both monitors I'm looking for are.

4@ P11221-ND CAP 820UF 25V ELECT FC RADIAL
2@ P12389-ND CAP 470UF 25V ELECT FM RADIAL

It's definitely a good idea to replace all the caps with the possible exception of the large (typically 120 uF, 450 V cap). First of all, there are several caps (10-100 uF, 50 V) that can fail with no visible signs. When they do, the result is a dead monitor. Since these cost under $.30 each, replacing them is not a significant expense.

Second, the caps are failing because of inferior quality. Again, the cost of replacing those with no obvious problems is minimal. And it will avoid having a problem when they also fail in a few years.

PlainBill

[almoodie]

Re: Twin Samsung 931b monitors

You'd better open it up again and make sure. Here are the Digikey part numbers and the Panasonic part numbers for the caps. Note most of them are available in two sizes. Choose First Class mail shipping for low cost and speedy delivery.

2 @ 820 microfarad 25V P11221-ND EEU-FC1E821 2 @ $1.07 OR P11222-ND EEU-FC1E821S 2 @ $1.30

1 @ 470 microfarad 25V P12389-ND EEU-FM1E471L 1 @ $.43 OR P12388-ND EEU-FM1E471 1 @ $.50

2 @ 1000 microfarad 10V P12353-ND EEU-FM1A102 2@ $.50 OR P12354-ND EEU-FM1A102L @ $.50

1 @ 330 microfarad 10V P11184-ND EEUFC1A331 1 @ $.48

1 @ 1 microfarad 50V P10312-ND EEUFC1H1R0 1 @ $.27

PlainBill

I will open it up again and double check, thank you sir.

Al Moodie.

[starmaxpc]

Re: Twin Samsung 931b monitors

I discharge caps using an axial leed 1k ohm resister with insulation on the leads and a blob of solder on the lead ends. Then short the capacitor leads with this resistor, count to 10 and your done.

i'd like to see a pic of that thingy..... would really be appreciated.

[Kevin O'Henly]

Re: Twin Samsung 931b monitors

See picture of the cap. shorting resistor.
rgs,
Kevin

[Pyr0Beast]

Re: Twin Samsung 931b monitors

Seems like this is a dual output board (13V (measures about 12.6V)), (5V (Measures about 5.3))

You can easily replace those 25V ones with 16V ones. 10V with 6.3V. General use capacitors where Low ESR is not needed. You might even get by cheap with replacing all with 16V 1000uF caps (if there is space)
Nothing is critical here. Not ESR, not Capacitance.
After the rectifier but before the choke (PI filter) keep low capacitance but high voltage-25V.
After the rectifier and after the choke, use caps rated at slightly higher than operating voltage (16V for 12V).
You may even leave the caps already there and replace only the ones bulged. It will
save you some work and the LCD should work just fine.
You need a good soldering iron to do the repair. I had problems with 45W, there are quite wide traces (helps a lot to heat with a dryer). Once the iron got really hot it worked flawlessly. Anything under 20W is just to weak.
Gas operated soldering irons are not worth it.

[Krankshaft]

Re: Twin Samsung 931b monitors

It really doesn't pay to leave any bad caps on the secondary they are cheap and it will save you the labor of having to do the same job twice.

Not to mention the black caps are also Crapxon its straight foolish to leave the same brand caps on that board that bulged.

When working with lead free boards I always wet the joint with some leaded solder to help the braid wick it away.

[Pyr0Beast]

Re: Twin Samsung 931b monitors

That is true as well.

[PlainBill]

Re: Twin Samsung 931b monitors

Seems like this is a dual output board (13V (measures about 12.6V)), (5V (Measures about 5.3))

You can easily replace those 25V ones with 16V ones. 10V with 6.3V. General use capacitors where Low ESR is not needed. You might even get by cheap with replacing all with 16V 1000uF caps (if there is space)
Nothing is critical here. Not ESR, not Capacitance.
After the rectifier but before the choke (PI filter) keep low capacitance but high voltage-25V.
After the rectifier and after the choke, use caps rated at slightly higher than operating voltage (16V for 12V).
You may even leave the caps already there and replace only the ones bulged. It will
save you some work and the LCD should work just fine.
You need a good soldering iron to do the repair. I had problems with 45W, there are quite wide traces (helps a lot to heat with a dryer). Once the iron got really hot it worked flawlessly. Anything under 20W is just to weak.
Gas operated soldering irons are not worth it.

With all due respect, that is REALLY bad advice.
It's going to cost less than $10 (including shipping) to replace all the caps on each board with first rate low ESR caps. While I do appreciate the value of a dollar, the fact is low ESR caps are required for the output of the SMPS. Reducing the voltage to save a few pennies and using general purpose caps sets the owner up for replacing the caps over again in a few years - or maybe even sooner. There is a thread here where someone used standard ESR caps to recap a monitor, and the inverter would shut down after a few seconds. Replacing the caps with high ESR caps solved the problem.

PlainBill

[Pyr0Beast]

Re: Twin Samsung 931b monitors

No, it is not the cost of capacitors. It is that this SMPS was designed to work with cheap capacitors and using LowESR in such circuits can be detrimental to the SMPS performance, especially in terms of ripple.

LowESR does not necessarily mean good performance nor long life.

Actually, you have to try it out. Sometimes it is better to make as little alterations to the circuit as possible.

[Wizard]

Re: Twin Samsung 931b monitors

Actually this SMPS requires low ESR at high freq. The capacitors placed in there when board is fresh was around .02-.06. Our shop services Samsung stuff so I have full access to new boards when ordered in to replace defects under warranty.

Cheers, Wizard