Samsung LN 40D630 TV - No Power

[jason123]

Hi Folks,
This might be a board replacement project, but wondering if other have had experience with this.
Picked up a Samsung 40D630 TV, no power. No Standby or other voltages on the PS board. The large caps are not reading any DC, and AC is showing 1.5 V

I found FM801S (cold side) fuse to be open. I replaced it, but no improvement, and the new Fuse is not blowing up.

PS board replacement, or is it worth troubleshooting the board (ideally, I'd love to, but I never had one with no voltage on the large caps before)

Thank you

[Andrew F. Ali]

Re: Samsung LN 40D630 TV - No Power

Is the fuse on the ac side good? Is your meter working with fresh batteries? Is the ac cord good?

[jason123]

Re: Samsung LN 40D630 TV - No Power

Valid questions.. yes, the AC fuse is shorted, and I'm reading good AC on both legs of that fuse. Meter is the one I use, and Yes, I use it to measure the AC.
Cord is good, and that was my first suspicion.. but another good cord shows the same symptom.

Incidentally, the Power Supply board is BN44-00464A - Can't seem to find schematic for it.
Thanks

[R_J]

Re: Samsung LN 40D630 TV - No Power

Remove the power supply and check the solder connections on the transformers like TM801S an components connected to the heatsinks.

[jason123]

Re: Samsung LN 40D630 TV - No Power

Solder looks ok. They must have some non-conductive coating on the heatsinks. Differential reading on the large caps, shows 162 VDC.. sorry about that.

Verified again that no voltages are present on the connector to the main board including the 5V standby. So main board is not getting any voltages.

Diodes on PS boards check out (at least that they're diodes ), no shorted FETs or Diodes that I could find. ESR checks out (low mOhm) on caps around the connector going to Main board.

Thoughts??

[budm]

Re: Samsung LN 40D630 TV - No Power

SMPS IC UM801S OK?, RM811 OK?
Fuse FM801S is in the HOT side not cold side, is for supplying the Voltage to run the SMPS IC and the inverter transformer driver circuit.
Are you 100% sure that FM801S is not blown again? It should have 160VDC with ref to the negative leg of the main filter cap in the cold side.

[CapLeaker]

Re: Samsung LN 40D630 TV - No Power

Verify again Pin 16 on CN802 for A5V. That's your STBY voltage. If there is nothing there, look at the standby circuit of the PSU. Also verify Pin 16 against GND (if there is a short or not).

[jason123]

Re: Samsung LN 40D630 TV - No Power

Not sure how to test UM801s, as i can't read the part number. Chip is in good physical shape and no shorts across pins. RM811 reads ~0.5 OHM. FM801S is definitely not open. Pin 16 definitely does not have any voltage. No short on pin 16.

I stumbled across some shorts that i don't think are right: DP807 AND CP804 are shorted in-circuit. Thanks

[CapLeaker]

Re: Samsung LN 40D630 TV - No Power

Does this IC on your last picture get power?

[jason123]

Re: Samsung LN 40D630 TV - No Power

No, pin 8 referenced to pin 6 (GND) or chassis, does not show any DC voltage (or AC) IC is SEM3040, and according to datasheet, pin 8 is vcc, correct?

[budm]

Re: Samsung LN 40D630 TV - No Power

Not sure how to test UM801s, as i can't read the part number. Chip is in good physical shape and no shorts across pins. RM811 reads ~0.5 OHM. FM801S is definitely not open. Pin 16 definitely does not have any voltage. No short on pin 16.

I stumbled across some shorts that i don't think are right: DP807 AND CP804 are shorted in-circuit. Thanks

You look at the wrong IC, the one you need to check is UM801S mounted on the heatsink. UP801S is for PFC.

Samsung BN44-00464A
https://www.shopjimmy.com/samsung-bn...pply-unit.htm#

[jason123]

Re: Samsung LN 40D630 TV - No Power

Thanks budm.. is there a datsheet for this UM801S? which pin is power I guess . Part number is not legible on the IC
Thanks

[jason123]

Re: Samsung LN 40D630 TV - No Power

please, does anyone has a circuit diagram for this BN44-00464A that they can share?

[budm]

Re: Samsung LN 40D630 TV - No Power

Thanks budm.. is there a datsheet for this UM801S? which pin is power I guess . Part number is not legible on the IC
Thanks

You cannot read anything printing on it at all? there must be something legible on it.

[jason123]

Re: Samsung LN 40D630 TV - No Power

Ok, got the better scope, and the part number is STR W6052S
Looks like datasheet is:

https://cdn.badcaps-static.com/pdfs/...d55e88614f.pdf

I am not getting any voltages on any of the pins. No VCC voltage

[budm]

Re: Samsung LN 40D630 TV - No Power

Pin 1 D/ST pin should have about 162VDC (if the IC is not switching) through the primary transformer winding which is fed the fuse that was blown earlier.

[jason123]

Re: Samsung LN 40D630 TV - No Power

0 dc on pin 1. AC is jumping around 3 to 44 to 2.4 to 0...is it the IC that's bad or transformer replacement you think?

[jason123]

Re: Samsung LN 40D630 TV - No Power

Naturally the new power supply board fixed the problem and the TV is working.. But would love to troubleshoot the Power Supply if at all possible.. if anyone has any ideas, or can share schematic.. I'd be appreciative.
Thank you

[budm]

Re: Samsung LN 40D630 TV - No Power

Well, you have good board and bad board for doing the resistance comparison readings.
Check that pin 1 of the SMPS IC again, it should have continuity all the way to that blown fuse.

[jason123]

Re: Samsung LN 40D630 TV - No Power

It does.. after taking the measurements yesterday, I guess the fuse did blow again. I also see that pin 1, 3, 5 and 7 of that IC are shorted.