Samsung PS51E490B1K No Display

[dick_barton]

The fault was described as a very loud bang and then no picture. Sound still working which has been verified by plugging in a DVD via it's SCART connector.

A visual inspection of the circuit boards did not immediately show any signs of damage. All low voltage supplies are up and running however VA, VSC, VE are all incorrect. The led on the control board blinks 1sec ON, 3sec OFF continuously.

With a meter check the following devices are short circuit.
Q5012, Q5003 (IGBT, FGPF4536)
D5005 (Diode, SF10A400H)

I think it's also best to replace Q5007 (IGBT, FGPF4536) as a precaution.
I believe the gate drivers are FAN73711 devices but without a schematic I'm not certain of the interconnections.

If anyone has a schematic they could share or failing that could suggest what other components should be replaced, it would be appreciated.

What other components would you check that could have been responsible for taking VS down.

Finally, can anyone tell me what the unit marked “Samsung R.5” shown in one of the pictures is?
Thanks

[ReeceyBurger123]

Re: Samsung PS51E490B1K No Display

I had the same set, was just the same Igbts and just them after replacing the set works fine

[dick_barton]

Re: Samsung PS51E490B1K No Display

Cheers ReeceyBurger123,
That sounds encouraging.

[ReeceyBurger123]

Re: Samsung PS51E490B1K No Display

Hopefully, just check the power devices for S/C almost never do the controllers get damaged. Also consider checking the Xmain and buffer for possible shorts.

[dick_barton]

Re: Samsung PS51E490B1K No Display

The final parts arrived today and were fitted after which I checked that there were no shorts between VA, VS, VE and ground. Powered up the set but once again only sound no vision.

On checking Va and VS, they were low as in my earlier post.

Next I checked the parts fitted and found that the IGBT Q5007 had gone short circuit. The board marking in front of the IGBT is YPS. All other parts tested OK out of circuit which was the complete reversal of the initial fault where Q5007 checked out OK but was only changed as a precaution.

Looking around the board I noticed that capacitor C5009 has the front of it blown off. It measures 330pf which may be the correct value since there are several identical looking capacitors marked 331K,1KV in that area. The diode it’s across checks out fine. Whether or not I missed this in the initial check I’m not certain.

Could anyone confirm that this is a 330pf, IKV ceramic capacitor.

I’ve checked the power supply disconnected from the X/Y boards.
Va = 57.8V, VS = 206.5V which I’ve now adjusted to the values given on the panel Va = 58V & VS = 201V.

Can anyone see why Q5007 would have blown on this occasion or can point me to a schematic for this model.
Thanks

Edit
Q5012 has since been soldered back in after taking the snapshot.

[dick_barton]

Re: Samsung PS51E490B1K No Display

Also found Q5037, K10A50D & Q5030 SMK630 both Mosfet short circuited.

[ReeceyBurger123]

Re: Samsung PS51E490B1K No Display

Hmm were they shorted before hand mate ? Also that cap value is correct btw. I never had this with mine I also suggest you check the Xmain for S/C again.

[dick_barton]

Re: Samsung PS51E490B1K No Display

I have a board out of another Samsung PS51E480 which to the naked eye appears to be identical. The faulty board from the PS51E490B1K is Rev AA6 and from the PS51E480 is Rev AA7.

C5009 on this board is 331, 1KV

Would anyone know if the boards are interchangeable.
Thanks

[dick_barton]

Re: Samsung PS51E490B1K No Display

Thanks Reeceyburger123,
I suspect that I did not do a thorough enough check initially and now suffering the consequences.

I'm very tempted to swap boards but will wait a while to see what others think.

[ReeceyBurger123]

Re: Samsung PS51E490B1K No Display

Hmm it should be interchangeable, maybe give it a try ?

[dick_barton]

Re: Samsung PS51E490B1K No Display

Hello ReeceyBurger123,
I'll leave it until the morning and then give it a go unless advised otherwise.
Thanks

[ReeceyBurger123]

Re: Samsung PS51E490B1K No Display

Ok mate

[dick_barton]

Re: Samsung PS51E490B1K No Display

The board swap appears to have done the job. So now to leave it run for a few hours before putting the back on.

Thanks for your help ReeceyBurger123 and I hope that this thread is now closed.