Samsung T240 No power. No Power Led turning on

[newbie1]

Hi guys,

Hope you guys are in good health..

Its been a while since I posted for assistance. Well, currently I am having a bit of problem of locating the faulty component/s of my on-going repair. I hope that someone can lead me the way here.

Monitor Model
Samsung T240. Power board images as attached.

Symptom/Problem
-No power. No Power LED turning on.

Plugged & measured Voltages
- across Big cap = 330V (330V)
No Secondary voltage whatsover
Tracing downstream found that reading of Q101 (FQFP7N65C) are
: D to -ve of Big Cap = 330V
: S to -ve of Big Cap = 0V
: G to -ve of Big Cap = 0V
: G to S = 0V
: Did not measure D to S as stated in the datasheet it is 650V !!!!. I could not afford to destroy my multimeter again.

Unplugged & measured resistances
- across R103 (beside Q101 colored orange-purple-silver-Gold) is 0 ohms (shorted). However, I am doubtful whether this is correct.

Description/what's been done.. or not
- Have not replaced all caps.. yet..

I have trouble also reading the markings on IC101. There are 3 line on it. I could only vaguely see AN7(orV)3X(unreadable). Therefore I could not distinguish the datasheet for it..

So am I on the right path to focus on whether the 2 components, Q101 (FQFP7N65C) & R103 (beside Q101 colored orange-purple-silver-Gold) are the caused of the fault on this Power board?. Or I am missing something else to check on?..

Hope the experts here can guide me along.. Let me know if more readings should be taken.
Thanks again..

[Rtech]

Re: Samsung T240 No power. No Power Led turning on

R103 being only 0.37ohms,can seem to look as though it is shorted, because of its very low value, But resistors go open circuit and not the other way.I would also take the Mosfet out of circuit and test it..the following may help if needed:-
http://www.4qdtec.com/mostest.html

[newbie1]

Re: Samsung T240 No power. No Power Led turning on

Thanks Rtech.. I will measure the MOSFET out of the circuit then.

[jetadm123]

Re: Samsung T240 No power. No Power Led turning on

If the mosfet checks good, then measure the value of Vcc on IC101 (4th photo).

[retiredcaps]

Re: Samsung T240 No power. No Power Led turning on

C109 looks like a 47uF 50V cap and is likely your startup cap.

1) What is the DC voltage across this cap? Red probe on positive leg, black probe on negative leg. Is this voltage stable?

2) With power off, see where the positive leg of C109 is connected to on IC101 (use continuity on multimeter to help). This is likely your VCC pin on the SMPS IC.

3) What is the DC voltage of the VCC pin? Use the negative leg of the large filter capacitor as ground.

[newbie1]

Re: Samsung T240 No power. No Power Led turning on

Jet, i was rushing off so did not measure the MOSFET out of the circuit but managed to squeeze time to measure the VCC (i think) of IC101. It is 1.22V

Greetings 'ever-reliable' retiredcaps,
You are spot on, sir. C109 is indeed 47uF 50V cap.
1) DC across it is 1.22V
2) C109 positive leg is connected to Pin 6 of IC101
3) VCC (Pin 6 of IC101) is 1.22V

I was also able to measure the rest of the pins of unknown IC101. All measurements were with respect to the negative leg of the Big cap (black probe placed there)
Pin 1 = 1.74V
Pin 2 = 1.55V
Pin 3 = 0V
Pin 4 = 0V (Gnd - i am sure this is linked to the negative leg of the Big cap)
Pin 5 = 1.2V
Pin 6 = 1.22V (VCC)
Pin 7 = 0V (seems to be non connected)
Pin 8 = 244V

So do you think that the IC is faulty? The problem is i could not tell what is the marking on this IC, even after shining lights & viewing on different angle using a magnifying glass...

[retiredcaps]

Re: Samsung T240 No power. No Power Led turning on

C109 is indeed 47uF 50V cap.
1) DC across it is 1.22V
2) C109 positive leg is connected to Pin 6 of IC101
3) VCC (Pin 6 of IC101) is 1.22V

1.22V is way too low for the SMPS IC to start. Assuming the power mosfet is good, then I suggest changing out the 47uF 50V cap first as it is the easiest and cheapest option and redoing the same measurements. My favourite is the Panasonic FC.

http://www.digikey.com/product-detai...0321-ND/266330

I'm expecting the startup cap to be in the 12 to 16V ballpark. It should be a steady voltage though.

[retiredcaps]

Re: Samsung T240 No power. No Power Led turning on

So do you think that the IC is faulty? The problem is i could not tell what is the marking on this IC, even after shining lights & viewing on different angle using a magnifying glass...

If the SMPS IC is faulty, your best bet is to search this forum and pray that my [/i]insistance[i] on clear focused photographs will help you find that part number.

Or you find a service manual with a schematic listing that part.

[retiredcaps]

Re: Samsung T240 No power. No Power Led turning on

Jet, i was rushing off so did not measure the MOSFET out of the circuit

You can do a simple "in circuit" test first to see if the pins are shorted between 1-2, 1-3, and 2-3.

[jetadm123]

Re: Samsung T240 No power. No Power Led turning on

IIRC, there are a few revisions of your power board. IC101 might be a FAN7602 PWM controller. Also, try the following:

1) with monitor unplugged and your meter set to resistance, measure across pins 4 an 6 (Vcc and ground) to if it's shorted.

2) if yes, then either IC101 is bad or one of the components connect to pin 6 is shorted to ground.

3) from your photos, there appear to be two zener diodes. One of them is probably connected to pin 6 of IC101. Check it for a short.

[newbie1]

Re: Samsung T240 No power. No Power Led turning on

1.22V is way too low for the SMPS IC to start. Assuming the power mosfet is good, then I suggest changing out the 47uF 50V cap first as it is the easiest and cheapest option and redoing the same measurements. My favourite is the Panasonic FC.
I'm expecting the startup cap to be in the 12 to 16V ballpark. It should be a steady voltage though. If the SMPS IC is faulty, your best bet is to search this forum and pray that my [/i]insistance[i] on clear focused photographs will help you find that part number. Or you find a service manual with a schematic listing that part. You can do a simple "in circuit" test first to see if the pins are shorted between 1-2, 1-3, and 2-3.

Retired, I have replaced the startup cap with a Panasonic FC 47uF 50V, but the voltage measurement of the individual pins of IC101 is still the same. I have looked through the 8-10 threads for T240 but none of the image is zoomed up to the IC101 for me to get a clear view of the marking. I have yet to find the part in the schematic that PlainBill (boy, really missed his intelligent & witty posts..) linked. I did the in-circuit test on the MOSFET but could not find any shorted between the D-G-S pins.

IIRC, there are a few revisions of your power board. IC101 might be a FAN7602 PWM controller. Also, try the following:
1) with monitor unplugged and your meter set to resistance, measure across pins 4 an 6 (Vcc and ground) to if it's shorted.
2) if yes, then either IC101 is bad or one of the components connect to pin 6 is shorted to ground.
3) from your photos, there appear to be two zener diodes. One of them is probably connected to pin 6 of IC101. Check it for a short.

Thanks Jet for the suggestion,
1&2) if I remember correctly I did the resistance check but could not see any shorting on either pins to the Gnd.
3) aaah.. ok.. I will check it for shorts (in-circuit) when I get home from work.

Also, I have looked up FAN7602PWM controller datasheet. Pin 8 (Vstr) is mentioned to be 600V but I am having 244V only on that same pin.. So I am not sure is it the correct controller or mine is just bad.. hmm.. I was thinking of removing the IC101 & pass it to someone here who has a microscope so that the marking on it can be ascertained. But the cons will be that I will probably destroy it & will be in trouble if the marking could not be figured out.

What do you guys think?

[retiredcaps]

Re: Samsung T240 No power. No Power Led turning on

Retired, I have replaced the startup cap with a Panasonic FC 47uF 50V, but the voltage measurement of the individual pins of IC101 is still the same.

Disconnect all your boards from the power board. Now remeasure the DC voltage on both the startup cap and the VCC pin on IC101.

[retiredcaps]

Re: Samsung T240 No power. No Power Led turning on

See if the following diodes are bad and possibly dragging down the power supply. Test each diode with the diode test function on your multimeter. Post the readings for the following components. You should have 2 readings per diode.

ZD101, ZD102, D103, D106, D102,

[jetadm123]

Re: Samsung T240 No power. No Power Led turning on

For Vstr, the max voltage fed to it can be up to 600V. The 600V is not what you should expect to see. If I looked at the same datasheet for the FAN7602 as you, then on Fig 25 you will see that Vstr (pin 8) is connected to your 330V through a resistor. There will be a voltage drop across that resistor, resulting in a lower voltage at pin 8.

Since you changed the startup cap and if you don't see any shorts on components connected to Vcc on IC101, then I would suspect IC101 is bad.

Also, have you checked Q101 for shorts yet?

[retiredcaps]

Re: Samsung T240 No power. No Power Led turning on

ZD101, ZD102, D103, D106, D102,

Also there is one around R105, but I can't make out the pcb designation.

PS. I love manufacturers who spend a little bit extra to get both sides of the pcb silk screened. It makes it easier to desolder and test components rather than test our spatial awarness and mapping skills.

[freecom]

Re: Samsung T240 No power. No Power Led turning on

dear friend

t-190
t-200
t-220
t-240

a lot off times problem is in mainboard

eeprom chip is problem

must do programmed again

i have that problem with t-190

was totaly dead

https://www.badcaps.net/forum/showthread.php?t=21275

[retiredcaps]

Re: Samsung T240 No power. No Power Led turning on

a lot off times problem is in mainboard

eeprom chip is problem

must do programmed again

While that might be true, newbie1's problem is he has no power, not even 5V standby. The main board requires 5V standby to work first.

[newbie1]

Re: Samsung T240 No power. No Power Led turning on

Dear freecom, thank you for your input. However, I agree with retiredcaps that my problem could be different with your’s

Ok guys, here are the diode readings taken in circuit with power unplugged:
Diode Reading 1 - Reading 2
ZD101 1097 - 626
ZD102 (flash a number then no reading) - 626
D103 159 - 159 (could be due to R17 in between it)
D106 (flash a number then no reading) - 571
D102 (no reading) - 532
D107 (diode near R105) (rising number then no reading) - 705

I also did it on Q101
D-S (no reading) – 575
D-G (flash a number then no reading) - (flash a number then no reading)
S-G (flash a number then no reading) - 887

Voltage across the start-up cap is the same when the main board is unplugged. If my understanding is correct, I could not see any shorting on the above diodes.

Jet, you are right. On my board there is also 3 SMD resistors (243) in series from the 330V to pin 8 of IC101. That could explain the drop in voltage.

Yes, retired. This is one of the better boards to work with. I had encountered some boards which will have the copper traces lifted when I desoldered the components. The boards I hate the most are those with no indicator on the connector of the secondary voltages pins to check on.

So any final thoughts, before I conclude that I should remove the IC101 from the board?
p/s : Retired, really appreciate you asking the other OP (Snev) on the IC101 marking. Would have done the same if you have not already done so.. thank you sir..

[retiredcaps]

Re: Samsung T240 No power. No Power Led turning on

Ok guys, here are the diode readings taken in circuit with power unplugged:
Diode Reading 1 - Reading 2
ZD101 1097 - 626
ZD102 (flash a number then no reading) - 626
D103 159 - 159 (could be due to R17 in between it)
D106 (flash a number then no reading) - 571
D102 (no reading) - 532
D107 (diode near R105) (rising number then no reading) - 705

A multimeter always gives a reading. There is no such thing as "no reading". If your multimeter is displaying "1" or "0L" on the left hand side of the lcd, it is telling you the measurement is "out of range".

D103 is suspect. I would remove it and retest to verify R17 is not affecting it.

BTW, the units above are in millivolts when the multimeter is in diode test function.

I also did it on Q101
D-S (no reading) – 575
D-G (flash a number then no reading) - (flash a number then no reading)
S-G (flash a number then no reading) - 887

It doesn't look like Q101 is shorted, but that doesn't mean it is working properly.

So any final thoughts, before I conclude that I should remove the IC101 from the board?
p/s : Retired, really appreciate you asking the other OP (Snev) on the IC101 marking. Would have done the same if you have not already done so.. thank you sir..

Many newbies never come back after the first post either because they don't check or subscribe to their own thread.

[newbie1]

Re: Samsung T240 No power. No Power Led turning on

A multimeter always gives a reading. There is no such thing as "no reading". If your multimeter is displaying "1" or "0L" on the left hand side of the lcd, it is telling you the measurement is "out of range".

D103 is suspect. I would remove it and retest to verify R17 is not affecting it.

BTW, the units above are in millivolts when the multimeter is in diode test function.

It doesn't look like Q101 is shorted, but that doesn't mean it is working properly.

Many newbies never come back after the first post either because they don't check or subscribe to their own thread.

oops!.. I believe the "no reading" should be out of range then because it is displaying "1".. I will check D103 again with one leg out of the circuit to confirm whether it is shorted.. if it is not shorted, i think there isn't much option except to replace the IC101 (whatever the component is) & Q101, right?.. I have read that the other OP could not read the marking on IC101.. Damn!.. Just my bad luck!..