Samsung 913V blinking LED

[Half-Saint]

Re: Samsung 913V blinking LED

I ask again: do you have the 13 volts

I don't know, haven't checked yet. Will try tomorrow.

also: when you checked the 5 volts that was going on and off along with the led - did you check it at pins 6 and 7 or at pin 9

I checked it on pins 6 and 7.

[Half-Saint]

Re: Samsung 913V blinking LED

My wife was in the hospital so I didn't have much interest in solving this.

Anyway, I measured voltage at pins 1 and 2 and it read 15.88V. Not quite what I expected.

Lift up one end of the jumper J308 (this will isolate the inverter power circuit from the power supply) and see if the 5V/13V become stable.

Yes, 5V became stable. 13V still reads more than expected = 15.28V.

[bammbammfran]

Re: Samsung 913V blinking LED

Sorry to hear about your wife, hope all is better !
need more info:
is that 5 volts and 15.28 with the c308 jumper disconnected and with the main board connected ?
If it is this: do you remember what the 15.28 was reading before the jumper was removed ? and is the power button led still flashing ?

[budm]

Re: Samsung 913V blinking LED

That means you need to check the MOSFETs (the two 8-pin SMD) which drive the inverter transformer. The 15.28 reading is about right without the heavy load (inverter circuit is not connected).
You need to check for S and D pins for shorts or very low resistance.
The 5V and the 13V are generated by the same transformer, so if the 5V is fluctuating, the 13V will be as well, the power supply was in shutdown/restart mode due to protection circuit detects over current drawn by the inverter circuit.

[Half-Saint]

Re: Samsung 913V blinking LED

Well, I'm back to trying to fix this guy... after fixing a 931BW by replacing all 8 caps, I'm thinking maybe recapping would do the job here as well.

931BW had only two bloated caps which I replaced but ended up with a monitor that would display the image for 2 seconds than go black. After replacing ALL caps, it works fine.

EDIT: replaced most caps but didn't have a replacement for 10uF 50V and 330uF 25V. The symptoms are still the same so maybe I'll have to take a look at those MOSFETs after all :-)

EDIT #2: is it OK to replace Samxon KM caps with Panasonic FC?

[bammbammfran]

Re: Samsung 913V blinking LED

is that 5 volts and 15.28 with the c308 jumper disconnected and with the main board connected ?
If it is this: is the power button led still flashing and will the power button actually work now

[Half-Saint]

Re: Samsung 913V blinking LED

I don't remember... after the recap, I reconnected everything (including the jumper) and just fired it up. Let me check and get back to you.

Test results - jumper disconnected, main board connected, backlight disconnected:
1) power button works
2) power LED stays on
3) 5V pin = 5V
4) 13V pin = 16.28V

[bammbammfran]

Re: Samsung 913V blinking LED

ok
then the transistors at U204 and or U205 may be an issue
what are the numbers on these two ?
and does your tester have an ohm setting

[Half-Saint]

Re: Samsung 913V blinking LED

ok
then the transistors at U204 and or U205 may be an issue
what are the numbers on these two ?
and does your tester have an ohm setting

Both MOSFETs are 4501GM and yes, my multi-meter has an ohm setting.

[bammbammfran]

Re: Samsung 913V blinking LED

ok
if you remove the jumpers at j308 and j318 where they almost touch each other
then set your tester to say 20k ohms
check those two 4501gm by probing the 4 pins on the one side that are all on the large solder areas( all 4 pins are connected together so any pin will do on that side) to the pins on the other side one at a time and compare one transistors readings against the other

[Half-Saint]

Re: Samsung 913V blinking LED

Just curious but why do I have to disconnect j318?

I'll try what you suggested tomorrow morning and report back.

[bammbammfran]

Re: Samsung 913V blinking LED

disconnecting the jumper will separate where the power feeds each chip on the 3rd pin so that you do not get a false reading on that pin when comparing the two

[Half-Saint]

Re: Samsung 913V blinking LED

I gave up on fixing this for a while then I found a seller from China selling "seller refurbished" boards for quite cheap. I decided to risk it and ordered one. The unit is obviously used and there's dust on the transformer.

The refurbish job was done MacGyver style. They replaced all 820uF 25V caps with OST 1000uF 25V. A 330uF 25V Samxon was also replaced with a 1000uF 25V. Not only was this cap 3x the size of the original, it was soldered the wrong way! I only noticed this after I plugged in the power and it started smoking.

The back side of the PCB has another story to tell. They shorted all four pins on one of the MOSFETs. There's also a connection between one cap and one of the jumpers. Presumably whoever did the job, destroyed the solder pad or the via (just guessing).

The screen now works but I wonder, if it's safe to use as is.

Thanks

[Jooo]

Re: Samsung 913V blinking LED

I only noticed this after I plugged in the power and it started smoking.

I hope you replaced that cap.

The back side of the PCB has another story to tell. They shorted all four pins on one of the MOSFETs.

You can see that all the four pins are on the same copper trace, so they were "shorted" like that when it came from the factory. Nothing to worry about that

There's also a connection between one cap and one of the jumpers. Presumably whoever did the job, destroyed the solder pad or the via (just guessing).

They probably lifted a pad there and just connected the capacitor lead to the closest solder pad, on the same copper trace. Doesn't look professional, but really is not a big deal.

Some of those solder joints don't look too good, I would resolder them.

[Half-Saint]

Re: Samsung 913V blinking LED

Yes, I replaced the dead cap with a 330uF 25V and the monitor works fine.

Thanks for the explanation. I'll resolder the joints on the caps just for some peace of mind.

[Agent24]

Re: Samsung 913V blinking LED

To keep it working, make sure you replace all the capacitors they put in with something better than OnlySomeTrash...

[Jooo]

Re: Samsung 913V blinking LED

To keep it working, make sure you replace all the capacitors they put in with something better than OnlySomeTrash...

If they are new, they should be OK for couple of years... But if they used second hand capacitors, yeah they may already be on the way out.

[Agent24]

Re: Samsung 913V blinking LED

If they are new, they should be OK for couple of years...

By which time you will probably forget about them. Decent ones are cheap, why take the risk? The crap ones are useful to keep for testing though, so long as they're still OK.