Hisense 50k680 no power no standby

[EUWest]

Hi folks!
Just got an Hisense 50k680 with no power and no standby. I dont get any dcv (ether 16dcv or 5dcv) to mainboard. Did some basic checks on diods and seems like there find.
On large caps C822 and C284 i get 315dcv. Is there a probleme on the cold side?

[dick_barton]

Re: Hisense 50k680 no power no standby

The problem looks like it's on the HOT (Live) side.

If you have no +12V then check the components around N851 (8 pin IC) and also V871. Dont lose the ferrite bead on the leg of V871.

[EUWest]

Re: Hisense 50k680 no power no standby

Tested V871 in circuit and seems like its fine. Do i have to solder it out and then test?
And cant finde N851. In schematic its listed but on Board cant see it

Edit//
Lol forgot to Look on backside. Will do some testings now

[EUWest]

Re: Hisense 50k680 no power no standby

Checked smd resistors nearby and get following results: in bracket will be value from schematic
R901 506k (1k)
R902 507k (1k)
R903 270k (1k)
R908 47 (27)
R909 75 (47)
R910 2k (2k)
R911 9.6k (10k)
R879 0 (0)
R963 0 (1k)
R964 1 (1k)
R881 0 (0)

Because there are many resistors differ from schematic value, is there problem somewhere Else or are smd resistors died?

[dick_barton]

Re: Hisense 50k680 no power no standby

What are the numbers on each of the resistors. Better still a photo of the underside of the board.
It is quite possible that the component values have changed and is dependant on the board revision.

[EUWest]

Re: Hisense 50k680 no power no standby

attached photo

[nomoresonys]

Re: Hisense 50k680 no power no standby

Resistor value: https://www.hobby-hour.com/electroni...calculator.php

[dick_barton]

Re: Hisense 50k680 no power no standby

They all apear fine and match your circuit except for R964 which you say is 1K and the board shows as 0 ohms. Double check and also check the zener diode VZ901 and transistor V901

Edit
Just re-read your results and R964 is down as 1 which I suspect you meant 1 ohm which is fine.

[EUWest]

Re: Hisense 50k680 no power no standby

R964 is about 1 ohm, not k ohm.
VZ901 is about 0.74 voltagedrop in diode Mode.

Found an theard where was similar Board with no power and standby. There was ic chip the problem.

https://www.badcaps.net/forum/showth...Hisense+55k610

Do i have to use chasis ground for testing Voltages from ic?

@nomoresonys thanks for your link, but didnt get how it could Help me

[nomoresonys]

Re: Hisense 50k680 no power no standby

Just put it up in case you had trouble knowing the value of resistors, couldn't tell exactly what your question was.

[EUWest]

Re: Hisense 50k680 no power no standby

Got it! Thanks, will Bookmark it

[dick_barton]

Re: Hisense 50k680 no power no standby

Do i have to use chasis ground for testing Voltages from ic?

No. Use the HOT ground which is the negative (-) leg of the 450V capacitor C822 (or of C824). Be careful the meter probe or clip you use does not slip.

[EUWest]

Re: Hisense 50k680 no power no standby

Is it possible to Plug ac cord to Power supply without installing it in to the Chassis? Otherwise how can i test ic voltage? Its on the backside i forgot

[dick_barton]

Re: Hisense 50k680 no power no standby

Disconnect the mainboard. Remove power supply and turn it over ensuring that it is well insulated from any possible metalwork that could cause a short circuit. Test with care.

[EUWest]

Re: Hisense 50k680 no power no standby

Weile testing R906 Burned so i dont now if my results are right or not.
I get on
Pin 1 (Skip/latch) : 0.34V
Pin 2 (FB): 0.34V
Pin 3 (CS): 0V
Pin 4 (Ground)
Pin 5 (DRV): 0.01V
Pin 6 (Vcc): 15.7V
Pin 8 (HV): 265V

Could this be correct?

[dick_barton]

Re: Hisense 50k680 no power no standby

R906 (has 102 printed on it) looks like a 1K ohm resistor so if you measure it you can tell if it's OK or not.
So the iC Pin 6 VCC has 15 volts which is a little low since the circuit says 20V but should be good enough for it to run.
Pin 5 which should drive the mosfet is not doing so.
Pin 3 should be monitoring the current through the mosfet via R912 (which you can check is not open circuit)
You said the mosfet V871 was OK so I'm suspecting N851 and would look at replacing it.

[EUWest]

Re: Hisense 50k680 no power no standby

Which ic should i order? Are in schematic is NCP1271D65R2G Listed, on PS its 1271A PSAG.
Online i found 1271D100R2G, should this okay?
R906 has now 280 k ohm, have to Replace it too

[dick_barton]

Re: Hisense 50k680 no power no standby

The NCP1271D100R2G looks good. It's an 8 pin SOIC device so should match yours in size.

[EUWest]

Re: Hisense 50k680 no power no standby

Just replaced NCP1271 but nothing changed. What else can it be?

[dick_barton]

Re: Hisense 50k680 no power no standby

Did you replace R906?
Do you still have +15V on pin 6 of the NCP1271