Samsung LN40E550 Dim Screen

[browserjoe]

Re: Samsung LN40E550 Dim Screen

DP805 measured 0.117 in both directions. Does it need to be removed from circuit and retested?

[vinceroger69]

Re: Samsung LN40E550 Dim Screen

yes remove or lift one side from the pcb and retest.

[CapLeaker]

Re: Samsung LN40E550 Dim Screen

If something tests weird in circuit, always take it out or lift a leg and retest it again.

[browserjoe]

Re: Samsung LN40E550 Dim Screen

Ok, might be awhile until I post back, think my soldering iron is broken, may have to get a new one.

Thank you for the help so far.

[browserjoe]

Re: Samsung LN40E550 Dim Screen

DP805 tested .455 forward and OL reverse.

[CapLeaker]

Re: Samsung LN40E550 Dim Screen

It should be good.

[budm]

Re: Samsung LN40E550 Dim Screen

DP805 measured 0.117 in both directions. Does it need to be removed from circuit and retested?

Can you check the resistance between the two pads of which the diode legs were soldered to when the diode is not connected?

[browserjoe]

Re: Samsung LN40E550 Dim Screen

314 ohms

[browserjoe]

Re: Samsung LN40E550 Dim Screen

Should I check DP804, QP801S, QP802S or RP821 next?

The only problem I see with removing QP801S or QP802S to test would be the giant glob of white adhesive on them.

[budm]

Re: Samsung LN40E550 Dim Screen

Check DP804, CP811.

[browserjoe]

Re: Samsung LN40E550 Dim Screen

Check DP804, CP811.

DP804 .343 forward, OL reverse

CP811 I'm having trouble testing, capacitance test seems all over the place. What is a good way to test these small ceramic capacitors?

[chrismurphy]

Re: Samsung LN40E550 Dim Screen

had a similar issue with 40 inch Samsung , turned out to be a faulty main board causing the backlights to go dim as you described , to fix i just cut the PWM control wire from the main board to the power board .....all fixed ,but the backlight is at full power and cant adjust but all good (saves replacing the board)

[budm]

Re: Samsung LN40E550 Dim Screen

If DP804 is removed, do you read 314 Ohms on the pads of the diode DP805 that you removed earlier?
"CP811 I'm having trouble testing, capacitance test seems all over the place. What is a good way to test these small ceramic capacitors?" We are looking for that leakage resistance of 314 Ohms.

[budm]

Re: Samsung LN40E550 Dim Screen

had a similar issue with 40 inch Samsung , turned out to be a faulty main board causing the backlights to go dim as you described , to fix i just cut the PWM control wire from the main board to the power board .....all fixed ,but the backlight is at full power and cant adjust but all good (saves replacing the board)

Right now he is getting only 164VDC on the main cap, the PFC Voltage booster is not working.

[browserjoe]

Re: Samsung LN40E550 Dim Screen

If DP804 is removed, do you read 314 Ohms on the pads of the diode DP805 that you removed earlier?
"CP811 I'm having trouble testing, capacitance test seems all over the place. What is a good way to test these small ceramic capacitors?" We are looking for that leakage resistance of 314 Ohms.

Pads for DP805 read 8.9 Mohms and it keeps rising slowly, CP811 is removed as well, should I put it back for this test?

CP811 reads 352 Ohms

[budm]

Re: Samsung LN40E550 Dim Screen

Pads for DP805 read 8.9 Mohms and it keeps rising slowly, CP811 is removed as well, should I put it back for this test?

CP811 reads 352 Ohms

Great, you found the problem, C8811 has leakage resistance, it should show as open circuit.
Can you tell what is printed on the body of the cap? It is high Voltage cap.

[browserjoe]

Re: Samsung LN40E550 Dim Screen

Great, you found the problem, C8811 has leakage resistance, it should show as open circuit.
Can you tell what is printed on the body of the cap? It is high Voltage cap.

LB 221k 1kv

[vinceroger69]

Re: Samsung LN40E550 Dim Screen

That capacitor seems a common failure as just been reading this thread
https://www.badcaps.net/forum/showthread.php?t=32636

[budm]

Re: Samsung LN40E550 Dim Screen

220pF 1000V.
http://www.digikey.com/product-detai...974-ND/4457538

I will go with 2KV one:
http://www.digikey.com/product-detai...022-ND/4457650

[browserjoe]

Re: Samsung LN40E550 Dim Screen

So when I removed the diode and tested resistance across the pads, was the 314 ohms a sign that there may be a bad capacitor?

And when I removed the capacitor and rested the pads and saw the high and climbing resistance (sign of a good capacitor?), was that the next capacitor in the circuit that was causing that?

Then testing the resistance of the capacitor after it was out and seeing it was close to the same ohms as when it was in circuit verified that is the problem?

Please feel free to tell me if I'm completely wrong , I'm just trying to understand some of this.