Samsung 242mp PSU problem

[Jont3]

Re: Samsung 242mp PSU problem

Maybe i should be more clear as the CP822 & CP826 read 0V when not working.

[selldoor]

Re: Samsung 242mp PSU problem

@pe9ghz Please can you post a picture of the bottom of your power supply board. Rename it pe9ghzPSBTM.jpg so we will know it is yours.

Please can you also check the values of your small caps & see if you have a 47uF 50v in there.

[Jont3]

Re: Samsung 242mp PSU problem

@pe9ghz Please can you post a picture of the bottom of your power supply board. Rename it pe9ghzPSBTM.jpg so we will know it is yours.

Please can you also check the values of your small caps & see if you have a 47uF 50v in there.

I would like to see the p/n number & revision ver to, since "mine" seems to be somewhat older and they could differ. I mailed samsung trying to get a schema for it, was redirected to convena who said there is no such avalibe, could order a spare from them but that isn´t all that fun, is it? :P

[selldoor]

Re: Samsung 242mp PSU problem

I have been looking at the soldering again and attach a picture for you check.

In the small section there is a blob which may just be on the surface or may have burnt through to the trace or it may be it should be there connecting something through the board. The resoldering within the large section may or may not touch the blob - does it and is it supposed to?
There are other bits as well which might need looking at - the rectangular blob (I think its the heatsink?) near the CP802S marker - probably just flux over the nearest trace but can it be cleaned off. Also the red component has a
whisker of solder on it - can you check its not touching anything you think it shouldnt. Looking at the board the middle of the "low voltage side" looks like it has been running hot so I would be inclined to recheck the soldering
in that area for a cold joint.

[retiredcaps]

Re: Samsung 242mp PSU problem

Not working:
8-4 0V, 6-4 0V, 1-4 0V

Working:
8-4 0V, 6-4 14,5V, 1-4 14,5V

It seems like pin 1 and 8 is not connected anywhere on the board, can it be another config than the one in figure 29?

My interpretation of the datasheet is that when the lcd is working pin 8 is turned off to save energy. Pin 8 is there for bootstrapping. See page 17, startup sequence.

A simple test can verify if pin 8 is connected or not.

1) Turn the power off and unplug the lcd.
2) Wait 3 minutes to let the large capacitor discharge.
3) Verify with your multimeter on DC voltage that the large capacitor has 0.0V voltage.
4) See if pin 8 has "continuity" or "beep" with the positive leg of the largest capacitor.

[Jont3]

Re: Samsung 242mp PSU problem

I have been looking at the soldering again and attach a picture for you check.

In the small section there is a blob which may just be on the surface or may have burnt through to the trace or it may be it should be there connecting something through the board. The resoldering within the large section may or may not touch the blob - does it and is it supposed to?
There are other bits as well which might need looking at - the rectangular blob (I think its the heatsink?) near the CP802S marker - probably just flux over the nearest trace but can it be cleaned off. Also the red component has a
whisker of solder on it - can you check its not touching anything you think it shouldnt. Looking at the board the middle of the "low voltage side" looks like it has been running hot so I would be inclined to recheck the soldering
in that area for a cold joint.

I´ve like tripple checked this since i posted the pictures, and did so again. it should be ok, and "beeping" (at right places) when tracing on board with DMM. There is no short its just flux and removed now.

My interpretation of the datasheet is that when the lcd is working pin 8 is turned off to save energy. Pin 8 is there for bootstrapping. See page 17, startup sequence.

A simple test can verify if pin 8 is connected or not.

1) Turn the power off and unplug the lcd.
2) Wait 3 minutes to let the large capacitor discharge.
3) Verify with your multimeter on DC voltage that the large capacitor has 0.0V voltage.
4) See if pin 8 has "continuity" or "beep" with the positive leg of the largest capacitor.

Lcd been unplugged over night when measuring, 450V cap 0,0V, No "beep" between pin 8 and 450V positive leg. Pin 1 & 8 does not have any trace on board (see picture). There is no wire trough board from "chip side" related to pin 1&8, since chip is located otherside of the 450V cap it is easy to check if any wires comming trough.

[Jont3]

Re: Samsung 242mp PSU problem

Been checking this board today and belive that this NCP1230 chip is not faulty. As i see this nothing will happen unless the opto-couplers are "on" and they are "off" when not working, optocouplers are driven by the 5V source that allways seems to work fine. This puts us in the cold part of the board and there are a couple of small TO-92 shunt regulators KA431AZ (US802 specially, resting against heatsink) ment to drain/source the leds in optocouplers (?). "way of the line" or could this be something? comments please included the smps sheet & Shunt, could be usefull maybe?

[selldoor]

Re: Samsung 242mp PSU problem

"included the smps sheet & Shunt, could be usefull maybe? "

There's a coincidence - I have been watching another thread
https://www.badcaps.net/forum/showth...997#post213997
and it is has the same smps and it has gone bad. In fact there are a number
of cases - different monitors -that have had problems with this chip or close relations. ( One exploded!!)

[Jont3]

Re: Samsung 242mp PSU problem

"included the smps sheet & Shunt, could be usefull maybe? "

There's a coincidence - I have been watching another thread
https://www.badcaps.net/forum/showth...997#post213997
and it is has the same smps and it has gone bad. In fact there are a number
of cases - different monitors -that have had problems with this chip or close relations. ( One exploded!!)

Yes! but still thinks mine is functional.....

Okay, this is what i found so far.

When lcd working:
It start out with a DM0365R getting 380V on PIN-5 |PIN-2 14V, |PIN-3 0,4V |using pin1 as gnd.
Then we have a DM0565R witch reads |PIN-4 9,3V |PIN-3 14,5V |PIN 5-6 NC |using PIN-2 as gnd.
And the NCP1230 chip as posted before

Not working:
DM0365R: PIN-5 301V |PIN-2 14V |PIN-3 0,4V
DM0565R, NCP1230 is just zero volts.

I´am still in looking at these opto-couplers since they are vital to DM0565R and NCP1230 circuit, they are not lit when lcd is in the "non working" mode. I did notice that discharging caps on cold side has a positive effect on getting it working again. Any sugestions?

[pe9ghz]

Re: Samsung 242mp PSU problem

@pe9ghz Please can you post a picture of the bottom of your power supply board. Rename it pe9ghzPSBTM.jpg so we will know it is yours.

Please can you also check the values of your small caps & see if you have a 47uF 50v in there.

I finally could take some pictures of the PSU board today.
I didn't want to scale them down (and loose sharpness), so I host them on my website (I hope this is OK):
pe9ghzPSTOP.JPG
pe9ghzPSBTM1.JPG
pe9ghzPSBTM2.JPG
pe9ghzPSmodel.jpg

I've searched the board for any 47uF caps, but there aren't any. Biggest ones are 22uF/50V:
CP804 22uF/50V at pin8 of IC801S (L6561D)
CP814 22uF/50V at pin2 of IC802S (FSDM0365).
CP822 22uF/35V at pin3 of IC803S (DM0565R).

I've also traced that the (15V) Vcc of IC801S (L6561) (pin8) and IC804S NCP1230 (pin6) are both obtained from UP801 (KA7815) which has a 100uF/35V near it's input.

The NCP1230 has a 10uF/50V between pin 6 and ground.

[PCBONEZ]

Re: Samsung 242mp PSU problem

Suncon should also have minus signs in the stripe on the side.
Sanyo didn't.
.

[selldoor]

Re: Samsung 242mp PSU problem

Evening chaps - thanks pe9ghz for the pictures and additional info. Looks like your board is a later revision. UnfortunatelyI dont know what the additional info means but perhaps it will help Jont3 .

What I have noticed is that one of you APPEARS to have a cap in the wrong way around, see attached.I get positionally challenged (aka lost) working from photos and trying to visualize where things are back of boards to front so ive not tried to prove my theory. Perhaps you can look at your boards and physically check if the diagram on the back of the board doesnt match the stripe on the cap.
What is odd is that I believe they usually pop if inserted the wrong way so maybe it is just another board variation but hopefully it will be good news for one of you.

[Jont3]

Re: Samsung 242mp PSU problem

As i'am digging myself deeper into the psu, beginning to think that it might be non faulty, i look at the signal board.... Never realized that it contain so many SMD electolytic caps, talking 50-60 caps. Varying from 100uf/35v and down to 4,7uf/16v. So trying to jumpstart this with on/off lead from signal board (in non working state) i get the 24v part going. Thinking about changing some of them to start with, since shorting 1st 35v/100uf cap on signal board actuallty makes it power up.... Atleast those three times i tryed... Any suggestions? Not going to do a full scale SMD replacement anyhow, those possible become legged variant.

[Jont3]

Re: Samsung 242mp PSU problem

Evening chaps - thanks pe9ghz for the pictures and additional info. Looks like your board is a later revision. UnfortunatelyI dont know what the additional info means but perhaps it will help Jont3 .

What I have noticed is that one of you APPEARS to have a cap in the wrong way around, see attached.I get positionally challenged (aka lost) working from photos and trying to visualize where things are back of boards to front so ive not tried to prove my theory. Perhaps you can look at your boards and physically check if the diagram on the back of the board doesnt match the stripe on the cap.
What is odd is that I believe they usually pop if inserted the wrong way so maybe it is just another board variation but hopefully it will be good news for one of you.

Naah, mine is right. The darker half circle on pcb i minus. Ooh yeah.... They pop and smoke

[PCBONEZ]

Re: Samsung 242mp PSU problem

Naah, mine is right. The darker half circle on pcb i minus. Ooh yeah.... They pop and smoke

Sometimes there are errors in the silk screen markings.
(As in the half circle for one or more caps can be wrong.)
.
That's why it's a good idea to make a cap map that includes polarity ~before~ you remove anything.
.
And they don't always actually pop or pop right away.
.
It would be a good idea to trace and draw out the circuit to see if it's right.
[Unless you can find some photos of your exact board that will show you.]
..

[PCBONEZ]

Re: Samsung 242mp PSU problem

what i have noticed is that one of you appears to have a cap in the wrong way around, see attached.i get positionally challenged (aka lost) working from photos and trying to visualize where things are back of boards to front so ive not tried to prove my theory. Perhaps you can look at your boards and physically check if the diagram on the back of the board doesnt match the stripe on the cap.
What is odd is that i believe they usually pop if inserted the wrong way so maybe it is just another board variation but hopefully it will be good news for one of you.

Good eye!

[selldoor]

Re: Samsung 242mp PSU problem

Hmm not sure it is the printing as I guess both sides differ - I dont know enough about circuits - how can they just change a cap around or are there some other major changes that I cant spot to make + - and - +
Attached pic of back with Caps marked.

[Jont3]

Re: Samsung 242mp PSU problem

Sometimes there are errors in the silk screen markings.
(As in the half circle for one or more caps can be wrong.)
.
That's why it's a good idea to make a cap map that includes polarity ~before~ you remove anything.
.
And they don't always actually pop or pop right away.
.
It would be a good idea to trace and draw out the circuit to see if it's right.
[Unless you can find some photos of your exact board that will show you.]
..

I checked all markings as i removed the old ones and they where correct, and i do have pics of it before so i can check if i would wounder. And no, in a PSU they will not often pop since there is not enough current for that, more like get varm and vent over time how fast depends on multiple factors still, a pop could happen .

Anyways, me thinking PSU was not right. Spent a whole weeks sparetime to check this PSU/chips/diodes etc with your guys help and the PSU is fully functional! Tripped over to the mainboard/signal board today and the IC602 (located on main/signal board) is my focus now, by applying a little pressure on it the lcd powers on and the second i let go of pressure it freezes the "no signal" dancing around on the sceen, will solder this and that tomorrow since i do not have the gear for that right now. Hopefully this has been the issue all along..... will drop a line here of the result.

[Jont3]

Re: Samsung 242mp PSU problem

Hmm not sure it is the printing as I guess both sides differ - I dont know enough about circuits - how can they just change a cap around or are there some other major changes that I cant spot to make + - and - +
Attached pic of back with Caps marked.

You really got the eagles eyes, thats a really good thing i think. This is a revision diff, but thanks!

[pe9ghz]

Re: Samsung 242mp PSU problem

Good news, guys!

Today I spent a lot of time trying to draw schematics of the PSU and later on doing some measurements trying to find the fault.
At first I measured a fast varying 9-11V at the Vcc pin of the DM0365R, but still no voltage was present on the secondary side after the rectifier diode for the 5V STDBY.
Later on, to my surprise, the 5V STDBY was measured a nice 5V-5.4V (edit: at this time, the Vcc of the DM0365R was measured a steady 14,7V. A good sign).
Very strange... This was the first time I measured the 5V STDBY to be present.

As no parts were changed in the meantime, it must be a bad contact/joint, so I decided to re-solder the pads in the area.
After doing this, the 5V-Stdby was stil working, so I connected the PSU to the Monitor and tried to power-on the monitor...
But nothing happened, except a high pitched tone (like the sound of a musquito) came from one of the transformers. The 5V-STDBY was still present, but the standby LED on the TV did not lit.

Tried to disconnect/reconnect some of the board connectors, and the last one I tried: the connector on the mainboard to the frontbutton-board was the culprit. After reseating this connector a few times, the pitch of the musquito changed.. And the monitor switched on !!

I've now reassembled the monitor and its currently still working.


If anyone is interested, I could scan my hand-drawn (chaotic) schematics and post them here.