Samsung LN32A450C1D Red light

[CraigR]

I have a Samsung LN32A450C1D with just the red light on and does nothing pushing the power button. I thought ok must be bad caps so looking at it all the caps look great so I pulled out the 7 big ones and checked with my ESR70 and all were perfect. I did check voltages and almost nothing on all of them. Fuse is good and no signs of anything hot or cold solder joints. Not sure what to check next.

[multimeter]

Re: Samsung LN32A450C1D Red light

any standby voltage?and for starters ,get rid of that brown glue around some of the components,it will conduct more as it gets older and cause problems

[CraigR]

Re: Samsung LN32A450C1D Red light

Not sure what one is standby on this connector but the ones marked 12v have nothing and the 2 marked 5.3v only have 1v approx.

[multimeter]

Re: Samsung LN32A450C1D Red light

ok,cant quite see them,5.3v is most likely the stb voltage,the 12v for the mainboard,.

disconnect main board loom,recheck voltages on the 5.3v rails on the power supply,do these re-appear?

[tom66]

Re: Samsung LN32A450C1D Red light

Think this is the schematic:


5.3V is generated by LM2576-ADJ (ICM856), a buck converter IC, from 24V rail.

Check-
pin 1: input voltage, around 24V.
pin 2: output switch node, approx 5.3V
pin 4: adjust, approx 1.25V

Also check pin 2 to ground for shorts, could be bad DM857
If input voltage present, but no output and DM857 not shorted suspect bad ICM856

[CraigR]

Re: Samsung LN32A450C1D Red light

tom66, you need to dumb it down a bit for me I have noware near your smarts. I can not get a prob in to check DM857 and I do not see ICM856 unless it's on the bottom of the board. Should I pull DM857 out of circuit and test??

[multimeter]

Re: Samsung LN32A450C1D Red light

tom66, you need to dumb it down a bit for me I have noware near your smarts. I can not get a prob in to check DM857 and I do not see ICM856 unless it's on the bottom of the board. Should I pull DM857 out of circuit and test??

in the pic,i think its next to the large filter cap,on a heatsink,3rd in from the left,

datasheet here www.hqew.net/datasheet/LM2576$2dADJ-datasheet-pdf-download-209961.html

[tom66]

Re: Samsung LN32A450C1D Red light

ICM856 will be mounted on heatsink near main board output connector.
DM857 will be near it.

Whenever testing a voltage is suggested but only a single point is given like above the measurement is to be taken with the red probe on the pin and black probe on the ground like the chassis of the TV.

Diodes are tested on the diode mode of your multimeter in both directions, note the readings you get.

[CraigR]

Re: Samsung LN32A450C1D Red light

Ok found it right next to DM857 and has 5 legs. Hard to see.

[CraigR]

Re: Samsung LN32A450C1D Red light

The 3 legs I can reach with my probe show only in the mV range.

[tom66]

Re: Samsung LN32A450C1D Red light

Pin testing may be easier if you solder wires to the pads underneath and test those instead.

[multimeter]

Re: Samsung LN32A450C1D Red light

The 3 legs I can reach with my probe show only in the mV range.

pin #1 is the VCC pin,check for input voltage

[CraigR]

Re: Samsung LN32A450C1D Red light

OK will pull board and solder on some test wires.

[CraigR]

Re: Samsung LN32A450C1D Red light

On DM857 I have 1v on the center leg and on MV on the other 2 legs.

[multimeter]

Re: Samsung LN32A450C1D Red light

On DM857 I have 1v on the center leg and on MV on the other 2 legs.

number pins 1-2-3

its a 3 legged duel diode

diode test on meter

measure pins 1-2 reading?

measure pins 2-1 reading?

measure pins 2-3 reading?

measure pins 3-2 reading?

[CraigR]

Re: Samsung LN32A450C1D Red light

And on the 2 legs of ICM856 I have 1V and the other in mV range.

[tom66]

Re: Samsung LN32A450C1D Red light

Which two legs?

[CraigR]

Re: Samsung LN32A450C1D Red light

1-2 =144 2-1=ol 2-3=153 3-2=OL


2 legs closest to heat sink.

[tom66]

Re: Samsung LN32A450C1D Red light

diode seems OK so ICM856 is the prime suspect, but need those voltages on 1,2 and 4 to be sure.

[CraigR]

Re: Samsung LN32A450C1D Red light

OK give me a min to put this back in the will tap ICM856 voltages.