Announcement

**momaka** · 08-25-2012, 04:13 PM

Re: Samsung Syncmaster 914v

Originally posted by KevinB550 View Post

From then on, the power LED would blink on and off, and each time it turns on there is a very faint, high-pitched whine before it blinks off and repeats the process.

I can only think of two issues for this:

Either the power supply start-up capacitor has gone bad (the start-up capacitor is usually a small 10 to 47uF 25 to 50 V rated cap)
*or*
The inverter transistors have gone short circuit, causing the power supply to shut down and keep restarting.

Since you don't have a multimeter, I would recommend that you replace those other electrolytic capacitors (the big electrolytic capacitor can be left alone, though). However, if that doesn't fix the problem, then you would need a multimeter to troubleshoot the issue. There are a lot of very cheap (under $10) multimeters on ebay. The cheap Chinese ones aren't that great and many members here will discourage you from getting them, including myself. However, if you have no other options, they should be fine for the job.

Also, if possible, can you post a picture of the other side of the power supply board?
It's possible that bad joints on the inverter transformers (the ones labeled TM-130) may also be part of the problem.

**KevinB550** · 08-25-2012, 05:23 PM

Re: Samsung Syncmaster 914v

Thank you very much for the reply!

Once I get back next week, it's very likely I'll replace the rest of the caps, assuming I haven't found anything else to suspect as the cause.

I tried to get some half-decent shots of the underside of the board, there's a plastic cover adhered to the board underneath the transformers so focus/glare were a bit of a nuisance there.

I didn't see anything that struck me as a cold joint on the transformers, however I noticed something I hadn't before, the last two pictures are attempted close-ups of it, C105 and R106 have leads barely touching, and I'm not quite sure if either they're meant to be and are just very loosely connected, or if they've fused and formed a short.

I've skimmed a few 20+ threads on other monitors, and I've noticed that some people replace caps with no luck, only to find that the pico fuse had blown and that simply replacing that solved their issue. Would you say this is a possibility if nothing else seems apparent? I'd have tested it already if I had a meter handy. A friend said to short it with a wire and see if it operated correctly, but I called him a madman.

If I get my hands on a meter, I already plan to test the fuse and the transformers, but what other tests would you recommend?

Thanks again!

Attached Files

**momaka** · 08-25-2012, 07:09 PM

Re: Samsung Syncmaster 914v

Originally posted by KevinB550 View Post

I tried to get some half-decent shots of the underside of the board, there's a plastic cover adhered to the board underneath the transformers so focus/glare were a bit of a nuisance there.

You can remove the plastic. Just make sure to put it back when you put the power supply back in the monitor again. Also, try taking just a single overhead picture of the underside that covers the whole board.

Originally posted by KevinB550 View Post

I didn't see anything that struck me as a cold joint on the transformers, however I noticed something I hadn't before, the last two pictures are attempted close-ups of it, C105 and R106 have leads barely touching, and I'm not quite sure if either they're meant to be and are just very loosely connected, or if they've fused and formed a short.

Are these the last 2 pictures you're talking about?:
https://www.badcaps.net/forum/attach...2&d=1345936258
https://www.badcaps.net/forum/attach...3&d=1345936751
If yes, I don't see anything wrong there.

Originally posted by KevinB550 View Post

I've skimmed a few 20+ threads on other monitors, and I've noticed that some people replace caps with no luck, only to find that the pico fuse had blown and that simply replacing that solved their issue. Would you say this is a possibility if nothing else seems apparent?

No, because (at least as far as I can see from the pictures you provided) you monitor has only 1 fuse - the mains fuse, that is. If that was bad, your monitor would appear completely dead (no blinking LED or anything). So that one is definitely not bad. The pico fuse those other threads mention is likely the inverter fuse - but again, if your monitor had one and if that went bad, the monitor would turn on and stay on just without the backlight. Your monitor turns on and off, judging by the blinking LED - that means either a bad start-up power supply capacitor or overload on the power supply.

With a single overhead picture of the underside, I can tell you which jumpers to remove to disable the inverter to see if your monitor can turn on. That would actually be a useful test since you don't have a multimeter. If the monitor stays on, then we know it's the inverter for sure.

Other than all of that, I think you should trim/shorten the leads on those caps you installed a little more to make sure they don't short out on to the case of the monitor.

Also, just FYI - NEVER short or bridge a fuse! Fuses are there for a reason - usually to protect the board from too much damage when something goes bad and to prevent things (including your house) from catching fire.

**KevinB550** · 08-25-2012, 07:34 PM

Re: Samsung Syncmaster 914v

Thanks again for the reply;

I was able to see between the board and the panel behind it when it was positioned exactly as it's typically seated, and the leads have a generous amount of space left, so I'm leaving them alone for now.

I tried to get a solid picture of the board, this time in another room where glare isn't as terrible. Really close shots were casting an unavoidable shadow on the board so I had to back off and zoom a little.

And aside from simple common sense, I knew from reading certain posts here that you don't ever want to bypass a fuse, hence my telling my friend he was nuts for suggesting it. I remember at least one guy in another thread that burned up a few IC's because he got impatient and shorted one with a length of wire.

I appreciate the suggestions so far, I've already invested a bit in the caps, a desoldering tool, and a spool of tiny-gauge solder and figured it couldn't hurt to ask here for any further advice before giving up on it. We may bring this thing back yet, and you've got my gratitude regardless!

Attached Files

**momaka** · 08-25-2012, 08:06 PM

Re: Samsung Syncmaster 914v

Great pictures, exactly what I needed!

Try removing jumper J308 (lifting one side of it will also work). This will disable the inverter. Then put back the power supply in the monitor and try powering the monitor ON. If the monitor turns ON and stays ON (that is, you won't get a picture on the screen, but the LED should stay ON solid and not blink), then there's something shorted on the inverter. If not, then there's something else wrong with the power supply.

**KevinB550** · 08-25-2012, 08:47 PM

Re: Samsung Syncmaster 914v

Seems like a pretty good call, freed one end of the jumper (making sure it couldn't contact anything) and closed it up, and just as you said, power LED stays on, doesn't seem to be "power cycling", and of course, no picture.

Is the likely issue the inverter transformers (TM-130's) then? Are they the ones whose windings, if they're still good, typically show a similar resistance to one another, something in the 1000 range?

**selldoor** · 08-26-2012, 05:06 AM

Re: Samsung Syncmaster 914v

Yes those TM-130s are the transformers to check looks like its now down to them but it could be the wiring or the bulbs - have you a spare one or an old panel or laptop screen with ccfls? did you pick up a meter yet?

**momaka** · 08-26-2012, 05:35 AM

Re: Samsung Syncmaster 914v

I would say the inverter driving transistors (U204 and U205 - the black rectangular 8-pin components) are the most likely culprit for the inverter to be causing a short like that. If it was the inverter transformers or the CCFLs, the inverter controller *should* have detected an overload/underload and would have shut down, leaving the monitor running ON without tripping the power supply short circuit protection.

At this point, a multimeter would be necessary to check the transistors for short circuit. Or if you are feeling lucky, buy a set of replacements and change them. That, however, doesn't guarantee they won't blow again because there may be something else wrong with the inverter that caused them to fail.

If you don't plan on using the multimeter for much more other than to fix this monitor, something like this would be a fairly reasonable buy:
http://www.ebay.com/itm/New-LCD-Digi...item232175a1ce
The only problem with these Chinese multimeters is that it may take a while to get to you from China. And they also don't have many or very good protections, so using them for anything but low-voltage, low-current applications shouldn't be avoided when possible.

That said, I do actually have a very similar cheap multimeter like that that was given to me about 12 years ago, and yet it still works fine to this day and I continue to use it, so these Chinese multimeters aren't all that horrible. I did have to repair the probes on it a few times, but other than that it's been reliable.

There's also these two, which are the same multimeters as the one above, but they ship from the USA so you get them much faster (of course, only if you're looking to buy, that is):
http://www.ebay.com/itm/Cen-Tech-7-F...item19d46f5b93
http://www.ebay.com/itm/CEN-TECH-7-F...item3f1b3b2d48

**selldoor** · 08-26-2012, 05:39 AM

Re: Samsung Syncmaster 914v

Can you do a pic of the panel board.

Re earlier post
@Momaka you say there wont be a picture on the screen ,I understand there will be no backlight but if it is all connected up and to a source should you be able to see a very dark image of the source on screen. That would prove main board and panel board were ok?

**momaka** · 08-26-2012, 06:10 AM

Re: Samsung Syncmaster 914v

Originally posted by selldoor View Post

@Momaka you say there wont be a picture on the screen ,I understand there will be no backlight but if it is all connected up and to a source should you be able to see a very dark image of the source on screen. That would prove main board and panel board were ok?

Yes, there should be a very faint picture on the screen. Very good call on that.
This will indeed verify weather the the rest of the monitor is working as it should be.

**KevinB550** · 08-26-2012, 07:19 AM

Re: Samsung Syncmaster 914v

Another good call, folks, I had checked for a non-backlit image before when it was still powering on/off, but I hadn't thought to once you had me disconnect the jumper. It is indeed there, so it looks like the damage is all but solved, if not the underlying issue.

Also, selldoor, are you referring to the long, narrow board along the top of the case? It's pretty much entombed under some plastic sheets held down with heavier glue than the one that was on the power board, but if you still need a close look at it, I can try and liberate it.

As far as getting a meter: the reason I'm going out of town is, as it turns out, for a job interview, so with any luck getting my hands on a meter will soon be a much simpler matter. If all goes well and I land it, I'll get myself a decent one as I've been wanting to for some time anyhow.

Is there a specific test to do on the transistors to verify that they've been done in? Any further action on my end is going to have to be Wednesday at the earliest, and in reality it will likely be several days after that, but I will be returning to this thread when I can.

You've been an amazing help momaka, and now selldoor too! And it's really starting to seem like you'll end up saving another monitor from the brink. You've both got my sincere thanks.

**selldoor** · 08-26-2012, 07:47 AM

Re: Samsung Syncmaster 914v

Originally posted by KevinB550 View Post

Also, selldoor, are you referring to the long, narrow board along the top of the case? It's pretty much entombed under some plastic sheets held down with heavier glue than the one that was on the power board, but if you still need a close look at it, I can try and liberate it.

No leave it for now - if your seeing a dark pic and we know there is a problem with the inverter section, it is hopefully ok.

Is there a specific test to do on the transistors to verify that they've been done in?

Nothing without a meter. - This is good to read if you havent seen it by retiredcaps
https://www.badcaps.net/forum/showthread.php?t=10419

start at post 19

Good luck with the job I would try and forget monitors and concentrate on that. We will still be here when you get back to it.

**momaka** · 08-26-2012, 09:03 AM

Re: Samsung Syncmaster 914v

Originally posted by selldoor View Post

Good luck with the job I would try and forget monitors and concentrate on that. We will still be here when you get back to it.

Indeed

. Once you get hooked on badcaps.net, you won't be able to get off so concentrate on the interview and I hope you do well.

**retiredcaps** · 08-26-2012, 06:10 PM

Re: Samsung Syncmaster 914v

Originally posted by momaka View Post

The only problem with these Chinese multimeters is that it may take a while to get to you from China. And they also don't have many or very good protections, so using them for anything but low-voltage, low-current applications shouldn't be avoided when possible.

Try NONE (protection). I bought that exact same multimeter. See my pictures and tell me if you want to use it.

https://www.badcaps.net/forum/showpo...7&postcount=28

If you don't have the money to buy a decent multimeter, borrow one until you save up $30 to $40.

**retiredcaps** · 08-26-2012, 06:14 PM

Re: Samsung Syncmaster 914v

Originally posted by momaka View Post

That said, I do actually have a very similar cheap multimeter like that that was given to me about 12 years ago, and yet it still works fine to this day and I continue to use it, so these Chinese multimeters aren't all that horrible. I did have to repair the probes on it a few times, but other than that it's been reliable.

12 years ago the quality was probably better than today. Today, my guess is a lot of fake parts or "B/C" grade components make it into 99 cent products.

The probes that I got with my 99 cent multimeter were never used and sat inside my kitchen cupboard, but the red probe still managed to fall apart after I took them out to use in another multimeter.

**momaka** · 08-27-2012, 11:06 AM

Re: Samsung Syncmaster 914v

Originally posted by retiredcaps View Post

Try NONE (protection). I bought that exact same multimeter. See my pictures and tell me if you want to use it.

I am already

Mine looks just as bad inside. The only difference is that since it's older, the components are all through-hole and not SMD - which is worse since some of their leads were very close to touching each other. However, one place where my multimeter is better is that the jacks for the probes are soldered on the main board and not on a daughter board connected with thin wires like yours. The solder joints are just as ugly, though. But for low-voltage and low-current measurements it's fine - provided that the multimeter works, of course. It's unfortunate yours didn't. But as with any other cheap item from China, the higher DOA rate is expected.

Originally posted by retiredcaps View Post

12 years ago the quality was probably better than today. Today, my guess is a lot of fake parts or "B/C" grade components make it into 99 cent products.

For cheap electronics like this, not really. It's pretty much still the same more or less. The only thing that has changed is the price and the volume produced - the volume per certain price has increased, hence why prices have dropped.

**KevinB550** · 09-05-2012, 07:17 AM

Re: Samsung Syncmaster 914v

Well, sorry about the wait, guys. Got back into town and went straight back out again with the girlfriend to visit with her family, got back from THAT and have spent the last couple days working through some computer issues of hers. I did manage to pick up a meter, and now that I've got a minute, I'm putting it to use!

I'm testing the two transistors for shorts, for U204 I'm seeing about 8.6M ohms between pins 1 and 2, and nothing within range (20M) between pins 1 and 3, and between pins 2 and 3.

For U205, it's about 10.7M ohms between pins 1 and 2, out of range between pins 1 and 3, ditto for pins 2 and 3. Are there more pairs I might test, or does this seem to indicate there's no short in either?

Proceeded to test the transformers.
For both T301 and T302, in the row of 6 pins, designating the pin closest to the edge of the board as Pin 1, I measured the following:
Pins 1+2: <1 ohm
Pins 1+3: Out of range
Pins 1+4: Out of range
Pins 1+5: <1 ohm
Pins 1+6: <1 ohm
Pins 2+3: Out of range
Pins 2+4: Out of range
Pins 2+5: <1 ohm
Pins 2+6: <1 ohm
Pins 3+4: <1 ohm
Pins 3+5: Out of range
Pins 3+6: Out of range
Pins 4+5: Out of range
Pins 4+6: Out of range
Pins 5+6: <1 ohm

For the 3 pins on the other side of each, none showed a resistance within range between themselves and any in the row of 6. The resistance between the outer two pins in each group of 3 was 1146 for T301, 1141 for T302. Definitely within a 3% tolerance.

Is anything amiss here that I didn't realize was such?

**retiredcaps** · 09-06-2012, 12:09 AM

Re: Samsung Syncmaster 914v

Originally posted by momaka View Post

Either the power supply start-up capacitor has gone bad (the start-up capacitor is usually a small 10 to 47uF 25 to 50 V rated cap)

As momaka suggests, check your startup cap.

The composition of the photo is too cropped, but I believe the startup cap is the one that I circled in red (just above the big cap)

Measure the DC voltage of the cap by placing your red probe on the positive leg and black probe on the negative leg of the cap. Report your reading.

Attached Files

**KevinB550** · 09-13-2012, 08:22 PM

Re: Samsung Syncmaster 914v

Hey again folks, sorry for yet another delay, I did indeed get that job and have been prepping for the move and have been neglecting my poor monitor

I had to test the startup capacitor from the other side of the board, as I can't get at the negative lead from the top. I had my lovely assistant hold it vertical and avoid grounding any components, but to get it in this position I had to disconnect it from the other board. I also still have the jumper disconnected from before, so that it doesn't reset itself constantly.

The capacitor seemed to be getting up to around 10-10.5 volts (taking a few seconds) before discharging almost instantly and repeating.

Announcement

Samsung Syncmaster 914v

Samsung Syncmaster 914v

Comment

Comment

Comment

Comment

Comment

Comment

Comment

Comment

Comment

Comment

Comment

Comment

Comment

Comment

Comment

Comment

Comment

Comment

Comment