Samsung LN32B460 turns on only after repeated attempts

[Dardo]

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?

I didn't catch the typo, but just assumed the CM804. By PS_on do you mean pin 1 on CNM802? That goes up to 1.8V on power attempts, then back down close to 0. There is another ribbon cable connected to the main board beside the one coming from the PS It disappears behind the metal shielding, but I assume it leads to the T-CON board. Disconnecting that cable has no effect on powering up.

[Dardo]

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.

INV ON/OFF goes to <0.5V on power on attempts, 4.7V on the one rare attempt that succeeded.

[retiredcaps]

Re: Samsung LN32B460 turns on only after repeated attempts

Check the voltage regulators on the main board (circled in red). My sig file has instructions.

[Dardo]

Re: Samsung LN32B460 turns on only after repeated attempts

Check the voltage regulators on the main board (circled in red). My sig file has instructions.

I tested them but I am having a hard time finding the data sheets. What I have so far...

IC105
78M098
KV 9A
8.84
0.00
13.07

IC427
119nB
17-18
0.00
1.811
3.26

[retiredcaps]

Re: Samsung LN32B460 turns on only after repeated attempts

78M098
KV 9A
8.84
0.00
13.07

http://pdf1.alldatasheet.com/datashe.../L78M09AB.html

78M09 is a 7800 series with 9V as the output voltage. At 8.84 it is 1.78% out. I use +/- 1% tolerance and others use +/- 2%. For now, assume it is good, but if you grasping at straws ...

IC427
119nB
17-18
0.00
1.811
3.26

17-18 is a 1117-18 fixed regulator. 1.8V should be the output voltage. IC427 is good.

[Dardo]

Re: Samsung LN32B460 turns on only after repeated attempts

Thanks, I was hoping I read those numbers right. Any other ideas?

[selldoor]

Re: Samsung LN32B460 turns on only after repeated attempts

If you turn the main board over there are a lot more voltage regulators on the back to test.

[Dardo]

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.

Since this does not go over 2V on power up, does that indicate a main board problem?

[tom66]

Re: Samsung LN32B460 turns on only after repeated attempts

Does it go high when it succeeds?

[Dardo]

Re: Samsung LN32B460 turns on only after repeated attempts

Does it go high when it succeeds?

Yes it goes to 4.7V when it succeeds, < 0.5V during unsuccessful attempts

[tom66]

Re: Samsung LN32B460 turns on only after repeated attempts

OK, so that pretty much puts the problem on the main board. Is there a part # for your main board - may be able to get schematics.

[retiredcaps]

Re: Samsung LN32B460 turns on only after repeated attempts

If you turn the main board over there are a lot more voltage regulators on the back to test.

Yup, I didn't even notice that. Good thing selldoor is our resident eagle eyes. 5 more to check.

[Dardo]

Re: Samsung LN32B460 turns on only after repeated attempts

OK, so that pretty much puts the problem on the main board. Is there a part # for your main board - may be able to get schematics.

Thanks Tom
There are 2 stickers with part #'s
BN97-03466B
BN96-11524A 657A

[Dardo]

Re: Samsung LN32B460 turns on only after repeated attempts

Yup, I didn't even notice that. Good thing selldoor is our resident eagle eyes. 5 more to check.

Thanks selldor and retiredcaps.
OK I checked the voltage regulators. I assume I need the readings when the screen is on, as some have power only when in standby.

IC601
1117
0944EG
pin 1 = 0.017
pin 2 = 1.264
pin 3 = 3.28

IC505
1117
0944EG
pin 1 = 0.631
pin 2 = 1.891
pin 3 = 4.75

IC109
17-33
0944DG
pin 1 = 0.017
pin 2 = 3.29
pin 3 = 5.10

IC106
17-33
0944DG
pin 1 = 0.017
pin 2 = 3.31
pin 3 = 4.75

IC110
7805AF
943
pin 1 = 8.82
pin 2 = 0.016
pin 3 = 5.05

I'm guessing there may be a problem with IC505?

[tom66]

Re: Samsung LN32B460 turns on only after repeated attempts

IC505 is fine - adjust measures 0.631V so output should be 0.631V + 1.25V(ref) = 1.881V. Actually 1.891V but that's fine.

As you are trying to track down an intermittent fault, try to get measurements with the TV "failed". So, when it fails to start up, measure the voltages while it is in this mode, before it goes back to standby.

[retiredcaps]

Re: Samsung LN32B460 turns on only after repeated attempts

IC505
1117
0944EG
pin 1 = 0.631
pin 2 = 1.891
pin 3 = 4.75

I'm guessing there may be a problem with IC505?

The readings say it is good. Re-read my link on how to test a voltage regulator.

1.891 - 0.631= 1.26.

Having said that, there is a possibility that the voltage on pin 1 is incorrect. The components feeding pin 1 could be off or pin 1 itself on the regulator can be bad.

Without a service manual, there is no way to be 100% sure.

The "common" output voltages are normally 1.25, 1.5, 1.8, 2.5 and 3.3.

1.891 is 5.05% out of tolerance when compared to 1.8. So if IC505 is really supposed to be outputting 1.8, then the regulator is bad.

edit: tom66 beat me -> I'm too slow today.

[tom66]

Re: Samsung LN32B460 turns on only after repeated attempts

The regulator should be OK, I have seen some Samsung LCDs which use 1.9V rails instead of 1.8V. Don't ask me why, though! The Vref is 1.26V, which is 0.8% out.

[Dardo]

Re: Samsung LN32B460 turns on only after repeated attempts

IC505 is fine - adjust measures 0.631V so output should be 0.631V + 1.25V(ref) = 1.881V. Actually 1.891V but that's fine.

As you are trying to track down an intermittent fault, try to get measurements with the TV "failed". So, when it fails to start up, measure the voltages while it is in this mode, before it goes back to standby.

The voltages are the same on failed startups.

[Dardo]

Re: Samsung LN32B460 turns on only after repeated attempts

Thanks for everyone's help. I'm thinking it is time to find a replacement main board, which is board # BN97-03466B, and the part # is BN96-11524A.
I'm finding 3 different part #'s for that board #
BN96-11524A
BN96-11524B
BN96-11524C

Does anyone know if I can use the B or C version, or if I need to stick with the A version?

[Dardo]

Re: Samsung LN32B460 turns on only after repeated attempts

Can anyone tell me what the part circled red in the pic is? Does anyone have a schematic?
Thanks