Samsung LA32B350F no backlight

[budm]

Re: Samsung LA32B350F no backlight

I got probably same problem as you I appreciate any help, by me are the voltages so
1. Power On/Off 0,76V <--> 0V
2. 5,15V
3. GND
4. 13.03V
5. GND
6. GND
7. 5,15V
8. 5,15V
9. GND
10. 13.03V
11. 13.03V
12. InverterOn/Off 5,11V <--> 0V
13. E-PWM 2,03V <--> 0V
14. DET_5V 0,12V <--> 0V
15. GND
16. GND

on big filterring capacitor i measure 309-310V I have repaced it for another one but get same voltage results

Is your AC line 120VAC or 230VAC?

[mrobo]

Re: Samsung LA32B350F no backlight

My AC is 220V
I measured all diodes, transistor, power resistors in power circuit and all seems good.
Electrolyte capacitors visualy seems good too.
By me the red power led blinks in tv stanby, when I power on the tv the red power led lights on, but no sound no screen picture, no lights.

[mrobo]

Re: Samsung LA32B350F no backlight

If voltage is too low the PFC circuit is probably not working or not getting enable signal

AC 227V input
DC 309V behind rectifier at input to PFC block

[budm]

Re: Samsung LA32B350F no backlight

AC 227V input
DC 309V behind rectifier at input to PFC block

How about the DCV right at the two legs of the main filter cap? You need to check it at the filter, not after the bridge rectifier in this case because we are dealing with PFC circuits.
It should be around 325VDC in standby.

[mrobo]

Re: Samsung LA32B350F no backlight

How about the DCV right at the two legs of the main filter cap? You need to check it at the filter, not after the bridge rectifier in this case because we are dealing with PFC circuits.
It should be around 325VDC in standby.

I have stated in previous post it is same 309V measured direct on capacitor and even measured connected to ground
Ho you know which voltage (325V?) should be there?
I am not 100% sure, but the voltage is probably same 310V standby and 309V when powered on, but will check again at monday at my work.

[budm]

Re: Samsung LA32B350F no backlight

AC RMS X 1.414 = APPROX DCV on the cap.
BTW, when making Voltage measurement in the hot side circuit, do not use chassis GND as the GND ref, the GND ref for the hot side circuit is the negative leg of the main filter cap.

[budm]

Re: Samsung LA32B350F no backlight

Check the resistance of those 3 PFC diodes to the right of that yellow main filter cap.
https://www.badcaps.net/forum/attach...1&d=1495111101

[mrobo]

Re: Samsung LA32B350F no backlight

AC RMS X 1.414 = APPROX DCV on the cap.

so:
227V x 1.414 = 320.978V
right?

[budm]

Re: Samsung LA32B350F no backlight

Yes, approximately yes.
Verify that main filter cap is good or not, or may the meter is not in calibration.

[mkhuzanie]

Re: Samsung LA32B350F no backlight

Check the resistor and zener >

[mrobo]

Re: Samsung LA32B350F no backlight

Check the resistance of those 3 PFC diodes to the right of that yellow main filter cap.
https://www.badcaps.net/forum/attach...1&d=1495111101

checked DP810=55.9KOhm, DP804=57.7KOhm, DP805=40,2KOhm
seems to me ok

[mrobo]

Re: Samsung LA32B350F no backlight

Yes, approximately yes.
Verify that main filter cap is good or not, or may the meter is not in calibration.

you can see on one picture that I have replaced it, but the problem continue
yellow capacitor changed to black capacitor

[mrobo]

Re: Samsung LA32B350F no backlight

Check the resistor and zener >

which resistor? all the resistor with greater wattage I have checked and are correct RM811=38,7KOhm, RM869=0.8Ohm, RP820=0.5Ohm
which zener and how you mean check it?
if you mean throughput thats seems ok I chcecked all diodes in circuit
none is interrupted by, none of them have short circuit

[mrobo]

Re: Samsung LA32B350F no backlight

When I inspected the other side of the circuit board where are smd parts I found out a little crack (not 100% sure if it is crack, but on the other two parts there is no so crack) on one part PC802S = NEC 2561A which seems to be PHOTOCOUPLER? (I don't know nothing about it), could someone tell me how to check it and what does the PHOTOCOUPLER, or tell me if I should search there for my tv problem?

[mrobo]

Re: Samsung LA32B350F no backlight

changed the CP809 = 47uF 50V and here are my new measurement

1. Power On/Off = 0.77V when stand by
1. Power On/Off = 0.01V when powered on
2. 5.3V = 5.14V when stand by
2. 5.3V = 5.15V when powered on
3. GND
4. 13V = 12.93V when stand by
4. 13V = 13.04V when powered on
5. GND
6. GND
7. 5.3V = 5.14V when stand by
7. 5.3V = 5.15V when powered on
8. 5.3V = 5.14V when stand by
8. 5.3V = 5.15V when powered on
9. GND
10. 13V = 12.93V when stand by
10. 13V = 13.04V when powered on
11. 13V = 12.93V when stand by
11. 13V = 13.04V when powered on
12. InverterOn/Off 4.75V when stand by
12. InverterOn/Off 0V when powered on
13. E-PWM 2.16V when stand by
13. E-PWM 0V when powered on
14. DET_5V = 2.44V when stand by
14. DET_5V = 0V when powered on
15. Sync 0V
16. GND

on big filtering capacitor i measure 396V when stand by -313V when powered on
also changed the schematic to this one:
https://www.badcaps.net/forum/attach...7&d=1343456910

could be the 5.3V compared to my 5.15V too low?

[budm]

Re: Samsung LA32B350F no backlight

All the Voltages and the control signals look OK to me.

[vinceroger69]

Re: Samsung LA32B350F no backlight

All the Voltages and the control signals look OK to me.

budm regarding his quote
on big filtering capacitor i measure 396V when stand by -313V when powered on

shouldnt the pfc voltage be the higher reading when the sets on?

[budm]

Re: Samsung LA32B350F no backlight

I think he reported it backward, it cannot be that high in standby.
Same thing for the Power ON/OFF signal, BL-ON (INV ON/OFF), PWM, DET5V.

[vinceroger69]

Re: Samsung LA32B350F no backlight

yes that makes sence now i have just re read his voltage readings

[mrobo]

Re: Samsung LA32B350F no backlight

I think he reported it backward, it cannot be that high in standby.
Same thing for the Power ON/OFF signal, BL-ON (INV ON/OFF), PWM, DET5V.

No, it is correct I am on AC 230V, the stand by (red power led blinks) and power on (red power led lights) voltages are correct
I am going MAD now, when I measured it again I get same 308V on stand by even when powered on.
302V in stand by - red power led on tv off
307-308V powered on - red power led on tv on
to be correct