samsung ln46a650 BN44-00203A psu part identification

[veikra]

I need help identifying these parts
The green resistor sit with one leg on either side of the relay power terminal. It blew up from a short circuit or current overload upstream.

The black inductors (deducted from symbol on board) I think they are the reasons for blowing fuses. These produce a .2ohm short between - and + of the big line capacitor if they are in circuit.

Might be a rabbit hole though! Need the green resistor to test

[tvtimmy]

Re: samsung ln46a650 BN44-00203A psu part identification

The green thing is a thermistor? The black things look like ferite beads to me. Somebody smarter will chime in with answers.

[budm]

Re: samsung ln46a650 BN44-00203A psu part identification

NTC, 5 Ohms cold resistance.
What is the diameter of that NTC?
The Ferrite bead is find, I would look for shorted semiconductors.

[veikra]

Re: samsung ln46a650 BN44-00203A psu part identification

NTC is 13 mm of diameter.

The ferrites causes a short between + and - of the big 450V capacitors, so I know the problem is probably over that side of the circuit which they feed

Downloaded the pdf, going through it

[veikra]

Re: samsung ln46a650 BN44-00203A psu part identification

Q816 was the short I was looking for. Diagram made is easy

[veikra]

Re: samsung ln46a650 BN44-00203A psu part identification

q816 and the ntc resurrected all low voltage. Tv runs but no backlight. Flashlight conclusive. Power on main 450V caps is low.

QI814 RI868 and ZDI805 blew up. What could cause this? They all sit around Q816. I dont think I missed seeing those when cleaning the board, but it is a possibility they already were.

[budm]

Re: samsung ln46a650 BN44-00203A psu part identification

Qi815 is connected in series with QI816, so for you to get shorts reading after the BI801/802 then QI815 has to have low resistance between S and D pin also.
QI815/816 form half-bridge drive circuit to drive the inverter transformer.
I would check QI815, DI810, 811, 813, 816, and the parts around the Gate drive of the MOSFETs'.
What DCV do you have on that main filter cap, 380~390VDC when TV is ON?
BTW, CI839 is the commonly failed cap.

[veikra]

Re: samsung ln46a650 BN44-00203A psu part identification

I had no short after replacing Q816. It's when it turned on that I got the issue. probably both side of the half bridge were shorted, replacing one solved the short, but only until the new mosfet turned on.

I have 400VDC at the main filter caps with tv on.

[budm]

Re: samsung ln46a650 BN44-00203A psu part identification

You should have replaced both of the MOSFETs and inspect all the parts connected to the Gate pin.

[veikra]

Re: samsung ln46a650 BN44-00203A psu part identification

yes, I did mess up.

One question, the ST version of the 2N7002 is 200ma, the ON semi version is 115ma.

Do you think I can use the lower power On semi since the ST is backordered?

[budm]

Re: samsung ln46a650 BN44-00203A psu part identification

It depends on how much current is being used in that circuit. Do you know which section that Transistor being used in?

[veikra]

Re: samsung ln46a650 BN44-00203A psu part identification

yes, it is used to pull the gate of QI816 down.
Unfortunaly I don't know what kind of voltage comes out of the transformer to calculate the current.

[budm]

Re: samsung ln46a650 BN44-00203A psu part identification

That is the Gate discharge MOSFET for the power MOSFET QI816 so the pulse current can be quite high, I owuld stick with original spec of the Transistor.
Is that the only device get damaged?
It is tested bad?
I expect ZI805 to be damaged too.

[veikra]

Re: samsung ln46a650 BN44-00203A psu part identification

That is the Gate discharge MOSFET for the power MOSFET QI816 so the pulse current can be quite high, I owuld stick with original spec of the Transistor.
Is that the only device get damaged?
It is tested bad?
I expect ZI805 to be damaged too.

It exploded and chunks of it flew off

yes the zener , the mosfet as well as the 4.7 resistor.

The schematics only says 2n7002. it's when I looked for a replacment that I found they were different amp rating with the same number

[veikra]

Re: samsung ln46a650 BN44-00203A psu part identification

FIXED!

So the NCT was shutting down all the low voltage and both QI816 QI815 shorted. Not replacing QI815 blew QI816 and RI868 ZDI805 RI866 and QI814.

The original failure was likely Q815 Q816 then the thermistor. Rest is my own fault but fuck it, ive got to release some blue smoke once in a while.

I used the 115ma mosfets 2n7002 since I couldnt get the other fast. Tv set is on test and I'll report how they do.

[budm]

Re: samsung ln46a650 BN44-00203A psu part identification

Glad to hear you got it working.
When Power MOSFET shorted out the GATE drive circuit should always be inspected and tested at the same time, and if the GATE is driven by the IC then the IC should also be replaced at the same time since it is not worth blowing the new MOSFET due to IC that is damaged when the MOSFET failed.
The NTC is for inrush current limiter when the TV is first turn on, it will blow if the load is shorted.
The NTC is bypassed by the relay when the TV is turned on so make sure that the relay is closing and bypassing that NTC.

[veikra]

Re: samsung ln46a650 BN44-00203A psu part identification

yes, relay is working correctly. I doublechecked all the mesurements from the pads of all the parts removed this time. Saw some 150 Ohms, checked around saw the resistors and followed the traces to make sure. These mosfets cost me over 2$ each
Tv has been running for 2 hours now. It starts cold with 2 vertical line when cold, but clears out after a minute or 2. Im not gonna fix that, flex ribbon, bga. Not worth the time.

Keeping this one to myself, replacing a 40 inch samsung that's running a toshiba main board and half of another powersupply. That thing is a beaut!