Samsung LN40A530 No Standby Voltage

[landyboy]

I got this Samsung that had a bad TCON very common for this model. Had the TCON repaired and set worked perfect for a few days, now I do not have any standby voltage. I've done some testing of the PSU and fuses are good but I'm not sure where the 5v SB should be coming from.

[budm]

Re: Samsung LN40A530 No Standby Voltage

Check caps CM802, 814, 815 capacitance and see how much DC voltage you have on them.
Zener ZDM802, 803 for leakage.
Sch provided by TOM66.

[landyboy]

Re: Samsung LN40A530 No Standby Voltage

CM802 12v
CM814 12v
CM815 12v

Not sure how to test Zeners for leakage.

[budm]

Re: Samsung LN40A530 No Standby Voltage

OK, so for sure you do not have standby output voltage at all?
The VCC startup Voltage is 22V, when power is first applied to the circuit, the startup cap at the VCC pin is charged through the HV pin of the IC with 1 mA current source, when it reaches 22V the SMPS IC will send the drive signal to the Gate, once it starts running, then the power will come from the AUX winding. If VCC is <25V or >11V, it will go into shutdown.
So it either that the Cap at the VCC has leakage or the internal current source of the IC is bad. I would check or replace those 3 caps first.
The SMPS IC is ICE2QS01.

[landyboy]

Re: Samsung LN40A530 No Standby Voltage

I have 12vdc at all 8 pins of that IC When testing each pin it starts at around 15vdc then slowly goes down to around 12v

[budm]

Re: Samsung LN40A530 No Standby Voltage

I have 12vdc at all 8 pins of that IC When testing each pin it starts at around 15vdc then slowly goes down to around 12v

That cannot be right. What did you use for the probe ground? You need to use the ground pin or the negative leg of the main filter cap because you are working on the primary side of the circuit.

[landyboy]

Re: Samsung LN40A530 No Standby Voltage

Ok unless I am still doing something wrong I used the ground pin with the same result on ICM802 12v all pins. I also tested between the negative lead of one of the two main caps and all pins tested 0vdc. I must be doing something incorrectly.

[budm]

Re: Samsung LN40A530 No Standby Voltage

Well that will make it difficult since I cannot see how you can be doing it wrong.
What DC voltage do you get when measure the directly right at the two legs of the main filter cap? It should be about 165~170VDC.

[budm]

Re: Samsung LN40A530 No Standby Voltage

"If VCC is <25V or >11V, it will go into shutdown." Typo in post 4
It should be:
If VCC is >25V = Over Voltage shutdown or <11V = Under Voltage shutdown.