Samsung - QN65Q7DRAFXZA

[jasenpeters]

2019 Samsung 65"
Q70DR 4k Smart QLED TV

Make: Samsung
Model No.: QN65Q7DRAFXZA
Version No.: FC02 / QRQ75
Serial No.: 08RH3CZM504979E
MFDate: May 2019

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Symptoms
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While TV on, a cracking noise heard, then no power, sound, or picture.

After back cover was removed, no visible burn marks or damaged components on power board (or other control boards (2))
On the power board (see attached)...

Fuse FP801S
T6.3AH250V

has no continuity (open circuit).


Any safe methods to jumper this in order to see if the TV will power up?

It may be a simple thing, but I don't want to risk blowing up the power board.
I assume the fuse broke for a reason, but nothing is visibly damaged on the power board.
Maybe the fuse just broke on its own only....

Any advice is appreciated.

[Biruslapio]

If there was a sound it may have been one of the small blue 1/2kv capacitors blowing up, they're covered in glue and can look fine even after popping, the transistors + their controller on the underside of the board near them may be damaged.

[EazyBone]

Is this a stock photo? You need the PSU to test the TV. If the power board blew everything else is likely safe. Get a new power board.

If you want to do component repair, check continuity on the MOSFETs on the hot sides. If there's continuity on any of the legs that's most likely your problem. Is that a stock photo or your actual photo? The pop could be a blue cap under the silicone they bury those stupid things

[jasenpeters]

Yes it is from a stock photo, however it's nearly identical to the photo I took (see attached).


The MOSFETS on the HOT side are:
2 - MagnaChip - 60R360Q - N-channel 600v, 0.36 ohm (both share the same heat sink alone)
2 - MagnaChip - 60R290P - N-channel 600v, 0.29 ohm (both share the same heat sink with U20A6CIC fast recovery diode)

I prefer component testing for now.

"If there's continuity on any of the legs that's most likely your problem."
I assume you mean a short across any of the Drain to Gate to Source terminals.

Any techniques to test the blue (tantalum?) Capacitors?

[jasenpeters]

The MOSFET (MagnaChip 60R290P) (Red Arrow) is shorted on all leads (GateDrainSource) in circuit.
The corresponding 2nd 60R290P MOSFET has values that may be affected by the shorted one mentioned before.

The other pair of MOSFETs (60R360Q) are matching in circuit values.

Any suggestions on safely removing the silicon goop covering the component?

[EazyBone]

Just cut it off, you can use plastic spudger or a utility knife. I tend to stick tweezers under there and start tugging it off after I cut with a utility knife gently. If you have them, best to change those 2 MOSFETs next to each other and the blue caps.

[jasenpeters]

While removing the white goop from the MOSFET (and it's neighbor to the left) I noticed that Capacitor to the left of the U20A6CIC fast recovery diode, was
blown out......there it is !!!

So, what do we do now, for component level repair?
- Remove the bad cap, and re-test the components for shorts
- Replace only what reads bad on/near this heat sink
- Just replace them all (on/near the heat sink), to err on the safe side (2-MOSFETS, 1-FRDiode, 4 Caps)

Thanks in Advance


PSU Board ------------------------------------>>> Can you see the bad Cap?

[EazyBone]

I would replace all 3 MOSFETs in this case, and all 4 blue caps.

[Biruslapio]

Remove the capacitor and if the mosfet is shorted, remove it too then probe the others for the same thing.
If it's in parallel to other MOSFETS then replace with the same part number, if not one with equivalent spec, max reverse voltage and current is enough.

[jasenpeters]

It's been a while. The parts took some time to get here....
The red arrows point to the component positions that had bad components that tested bad even after removed from the circuit.
MOSFET shorted on every leg. Capacitor exploded.

However, all components on the heat sink were replaced (2 - MOSFETS, 1 - FRDiode), and the supporting capacitors (4 - 221 2kV)

Okay, so I realize that (after inspection and in circuit testing early on) the fuse near the power plug FP801S, had an in circuit reading of open (infinity ohms).
The board shows T6.3AH250V near the fuse.



The web suggests this is ceramic slow blow fuse common in these applications.

Any suggestions on how to power test the new components safely considering the fuse is blown?
Some kind of safe by-pass method or just wait it out for the order of fuses to come in....?

Thanks in Advance

[EazyBone]

Wait for fuses. If you replaced those MOSFETs and the caps then you should be good. The way to bypass it is just solder a paperclip directly across and plug it in... But that would be stupid to do because IF something was bad.. the fuse is your defense. I have "fixed" something before and plug in and fuse immediately blows. So if I did this I would of damaged the board. It's how you keep the board safe.. so wait for fuses.

Also everything looks good on the top side, can't see bottom cause no picture.. but looks good. You used heatsink paste yes? Looks like it

[lotas]

It's good that you didn't supply power to the power supply, it would have been a good bang! Why did you install non-insulated housings on mosfets, you now have a short circuit between the transistors and a short circuit to the radiator housing (GND)! (2 Pin (Drain) is connected to the body of the transistor itself).

[EazyBone]

Oh wow, didn't even see or know that would be a problem. More pics!

[jasenpeters]

Iotas...

I think you're on to something there....Drain (pin 2) shorted straight to ground. YIKES !!!
Is there a insulation method / material / device to apply here?
Or, should I order new ones that are insulated?




EazyBone....
Land side of PSU....


Thank you both for your advice, and any others who want to chime in.

[lotas]

You need this (isolator)...