Samsung LN32B460 turns on only after repeated attempts

[Dardo]

My 2 year old Samsung LN32B460 recently started turning on only after multiple times pressing the power button.
I press power and the standby light will blink off for about a second, then blink on and off quickly then stay lit. It will usually do this 2 or 3 times after each press of the power button. Eventually it will turn off for a second, on again and finally back off and the set will turn on. There are no problems once it is powered on.
It is not one of the Samsungs know to have problems turning on due to bad caps, and there is no clicking sounds when turning on. I pulled the power supply out looking for bad caps, but found none that looked suspect.
Any ideas what the problem might be, or what my next steps should be?

[budm]

Re: Samsung LN32B460 turns on only after repeated attempts

Can you post good clear pictures using attachments, not posting in line?
Bad caps can look normal but they can have high ESR, you will need ESR meter to test them.
We will need to check the voltages when it does not work and when it is working to see what is going on.

[Dardo]

Re: Samsung LN32B460 turns on only after repeated attempts

Thanks for the reply Bud. Unfortunately I do not have an ESR meter, but I can replace the caps if they are the most likely problem. I do have a good multimeter to test voltages, if i know exactly where to test. I am attatching some images of the ps board and one of the main board.
Thanks again

[budm]

Re: Samsung LN32B460 turns on only after repeated attempts

I would try this next before trying to replace the caps. Use the hair dryer set to low and then blow it around the caps and see if the TV will turn on OK.

[Dardo]

Re: Samsung LN32B460 turns on only after repeated attempts

I tried the hair dryer with no visible difference. The problem only seems to be getting worse...it will only turn on every 10 or so attempts now. Any other suggestions what to try next?
Thanks

[tom66]

Re: Samsung LN32B460 turns on only after repeated attempts

Try cleaning the power button - does the same thing happen with remote control?

[Duncanbest]

Re: Samsung LN32B460 turns on only after repeated attempts

If the switch board is OK, maybe one of PHOTOCOUPLERs on power board is NG.
(The standy +5V PHOTOCOUPLER is good.)

They are not seen in the pic. -->SMD type in other side.

[Dardo]

Re: Samsung LN32B460 turns on only after repeated attempts

Thanks for the replies. Now the standby light only blinks a few times after pressing power...it won't turn on after many attempts.

Tom - I get the same response using the power button or the remote.

Duncan - I have posted pics of the back of the PS and main boards. Can you point out which photocouplers and how to test or diagnose if they are the problem?

[Duncanbest]

Re: Samsung LN32B460 turns on only after repeated attempts

Power board (in the middle) mark PC801S PC802S PC803S are photocouplers.

You can download PC817 or PS2561AL-1 datasheet to verify .(or read the mark to find the correct photocoupler.)

How to test? -------- I really don't know.

I always replace with new component (try & error),seldom use meter to check.

[selldoor]

Re: Samsung LN32B460 turns on only after repeated attempts

To do a proper check you need an analogue meter however you can do a very basic test with a multimeter set on diode - NO power to the set - test across the secondary cold
side and report result.
I am wondering if it is just the startup cap failing. On the primary hot side one of the small caps should be 50v 10 47 or 68uf is usual - I would change that.
Schematic for this board is here

[Dardo]

Re: Samsung LN32B460 turns on only after repeated attempts

To do a proper check you need an analogue meter however you can do a very basic test with a multimeter set on diode - NO power to the set - test across the secondary cold
side and report result.
I am wondering if it is just the startup cap failing. On the primary hot side one of the small caps should be 50v 10 47 or 68uf is usual - I would change that.
Schematic for this board is here

Sorry I'm a noob at repairing electronics. You mean test each pin on the connector leading to the main board I assume?
There are 3 50v 47uf caps and one 50v 22uf cap on the hot side, is the 22uf one the startup cap (CM808 on the schematic you provided)?

Thanks

[budm]

Re: Samsung LN32B460 turns on only after repeated attempts

You power supply is almost the same as this:
https://www.badcaps.net/forum/showth...hlight=SAMSUNG

The startup cap is the ZM804 47uf 50V.
Loo at the voltage on the main DC filter cap CP 815, it should have 165~170VDC hwen TV is plugged in, then it should go up to about 400VDC when power switch is activate, look at pin1 of CNM802, you should have steady 3VDC or more when power switch is activated, so look for that when you first activate the power switch, if it is there and the TV still does not come on, the it will be the problem in the PFC not getting the power to kick it on.

[Dardo]

Re: Samsung LN32B460 turns on only after repeated attempts

You power supply is almost the same as this:
https://www.badcaps.net/forum/showth...hlight=SAMSUNG

The startup cap is the ZM804 47uf 50V.
Loo at the voltage on the main DC filter cap CP 815, it should have 165~170VDC hwen TV is plugged in, then it should go up to about 400VDC when power switch is activate, look at pin1 of CNM802, you should have steady 3VDC or more when power switch is activated, so look for that when you first activate the power switch, if it is there and the TV still does not come on, the it will be the problem in the PFC not getting the power to kick it on.

Thanks Budm
I get readings on CP815 of 162VDC plugged in, 378VDC when the power button is activated.
On pin 1 of CNM802 I get 1.18VDC when the power button is activated.

[tom66]

Re: Samsung LN32B460 turns on only after repeated attempts

378V, even if set doesn't power up fully?

[Dardo]

Re: Samsung LN32B460 turns on only after repeated attempts

378V, even if set doesn't power up fully?

Yes, it goes to 378V while the standby light flashes for a few seconds, then back to 162V. If plugged in when CNM802 is disconnected, the backlight comes on and it reads a constant 378V.

[tom66]

Re: Samsung LN32B460 turns on only after repeated attempts

OK, what about the other supply voltages, like 13V?

[selldoor]

Re: Samsung LN32B460 turns on only after repeated attempts

The startup cap is the ZM804 47uf 50V.
.

ZM804 is a zener diode on the secondary side I think Budm means CM804

[Dardo]

Re: Samsung LN32B460 turns on only after repeated attempts

OK, what about the other supply voltages, like 13V?

The 13V all get 13V when the power button is activated, the 5.3V get 5.1V.
Standby gets a constant 5.1V

[budm]

Re: Samsung LN32B460 turns on only after repeated attempts

You are right, I made the typo, it should be CM804. But since the backlights do come on and the boost voltage is OK, then something on the main board is telling it to turn off the PS_ON signal so the votgae goes back down to 162V if I read post 15 correctly, but I do need to find out if at the same time the PS_ON also goes down. I think the problem is in the main board. Does it stay on if the T-CON board is disconnected?

[tom66]

Re: Samsung LN32B460 turns on only after repeated attempts

I would suspect main board problems then. Everything on the PSU seems to be fine. One final check - INV ON/OFF does this go HIGH (>2V) on every power up or just the ones that succeed.