Samsung LA26R71BA cannot power up

[john_doe]

Re: Samsung LA26R71BA cannot power up

Hi dick_barton,

With PS_ON connected to standby 5.2 vdc, the voltage at the big cap is 63 vdc.

[dick_barton]

Re: Samsung LA26R71BA cannot power up

In post #34 the voltage was 323V? so with PS_On connected to 5.2V did this voltage rise??

[john_doe]

Re: Samsung LA26R71BA cannot power up

It dropped to 63 vdc. It is still connected to the dim bulb tester.

[dick_barton]

Re: Samsung LA26R71BA cannot power up

I generally don't use the bulb so perhaps Vincerogers69 can answer.
If it's falling to 63V then I assume it's at 323V prior to connecting PS_ON.
Connecting PS_ON then drops the voltage to 63V so the PFC circuit must be switching on because current is flowing through the lamp and dropping most of the voltage across the lamp which then becomes brighter.

I would with caution remove the lamp, replace the fuse and try again and hope everything is OK. The voltage at the capacitor should rise when PS_ON is connected.

You may wish to wait to hear from Vincerogers69 before trying.

[vinceroger69]

Re: Samsung LA26R71BA cannot power up

i would try it now with out the bulb tester as you have your five volts standby etc i usually find if theres a short circuit the bulb lights full brightness straight away.
with no short the bulb should just barley glow if thats the case i usually remove the bulb replace the fuse and power on.

[dick_barton]

Re: Samsung LA26R71BA cannot power up

i would try it now with out the bulb tester as you have your five volts standby etc i usually find if theres a short circuit the bulb lights full brightness straight away.

Thanks for the confirmation Vincerogers69.

[vinceroger69]

Re: Samsung LA26R71BA cannot power up

Im still learning myself but using a dim bulb tester does seem to save parts if you have missed a faulty item maybe budm will confirm the bulb wattage we should be using and what to expect as in bulb brightness etc under diffrent circumstances.

[john_doe]

Re: Samsung LA26R71BA cannot power up

I disconnected the bulb tester but with 1k resistor still connected from PS_ON to standby 5.2 vdc.

As soon as i power up, i blew up NT811S.

[dick_barton]

Re: Samsung LA26R71BA cannot power up

Now that I did not expect!!! The NT811S is the inrush current limiter.

[dick_barton]

Re: Samsung LA26R71BA cannot power up

Can you check QP801S, QM801 & QM802 with the set off using your meter on ohms to see if any of them are short circuit.

[vinceroger69]

Re: Samsung LA26R71BA cannot power up

What new parts have you fitted to this psu already?

[john_doe]

Re: Samsung LA26R71BA cannot power up

With multimeter set to ohm, the resistance across CP802 is 30k ohm.

For QM801 and 802, pin 1 to 2, the resistance is 3M ohm. Pin 1 to 3 is 11 ohm and pin 2 to 3 is 3M ohm.

Ì replaced FP801A, ICP801S and QP801S. Total 3 new parts.

[dick_barton]

Re: Samsung LA26R71BA cannot power up

Sorry, my mistake, the first components should have been QP801S
QM801, QM802 look fine.

Can you show a close up photo of ICP801S

[john_doe]

Re: Samsung LA26R71BA cannot power up

For QP801S,
Positive Negative
Pin 1 to 2= 290k ohm
Pin 1 to 3= 99k ohm
Pin2 to 3 = 400k ohm

[dick_barton]

Re: Samsung LA26R71BA cannot power up

Isn't QP801S the mosfet that you originally replace.

[john_doe]

Re: Samsung LA26R71BA cannot power up

Pic of ICP801S

[john_doe]

Re: Samsung LA26R71BA cannot power up

Yes, i replaced QP801S.

[dick_barton]

Re: Samsung LA26R71BA cannot power up

For QP801S,
Positive Negative
Pin 1 to 2= 290k ohm
Pin 1 to 3= 99k ohm
Pin2 to 3 = 400k ohm

Something does not make any sense.
If the mosfet did not go short circuit then what caused the NT811S and fuse to blow!!!

Could you check with your meter the resistance between Pin 1-2, 2-3, 3-4,4-5 etc for ICP801S and what is that shown on pin 4?

[vinceroger69]

Re: Samsung LA26R71BA cannot power up

for future refrence ive just saw this post tom66 wrote about using a dim bulb tester
The lamp glowing indicates current is being drawn.
Once the lamp goes out, very little current is being drawn.

If there was a short, the lamp would be on continiously. So it should be OK.

Most power supplies will do one of several things:
- The lamp may flash or flicker
- The lamp may glow once then go out once the main capacitor has charged up.
- The lamp may glow dimly and the TV may operate (usually smaller TVs will run with a 100W bulb, larger ones may not work or may require a much larger bulb, 150-200W or so)

Now there is one exception, if the TV has a relay on the power board which may turn off, there could be a short beyond this relay. If there is a relay, you want to find some way to keep it on continuously.

so it depends how bright the bulb was glowing maybe something else was still short? its hard when we cant see things ourselves as in how bright the bulb is etc

[john_doe]

Re: Samsung LA26R71BA cannot power up

Resistance
Pin1 to 2 = 8.3M ohm
Pin2 to 3 = 5.6M ohm
Pin3 to 4 = 12.25k ohm
Pin4 to 5 = 22.4k ohm
Pin5 to 6 = 22.1k ohm
Pin6 to 7 = 99.5k ohm
Pin7 to 8 = 106k ohm

The thing on pin4 is solder.