Samsung LA32B350F no backlight

[vinceroger69]

Re: Samsung LA32B350F no backlight

im on 230v ac myself your voltage readings dont make sence too me with tv pfc psu s i get roughly 325v in standby and roughly 390v when the sets running

[mrobo]

Re: Samsung LA32B350F no backlight

you got right guys it is conversely i made mistake with the red power led on tv
it is so: when the tv is in standby the red led lights on
when I power on the tv the red led 5x times blink and stays off
sorry my mistake

[mrobo]

Re: Samsung LA32B350F no backlight

ok new measuremets (my input is 227V AC I am from EU):
in stand by:
CP815 = 304V
1. Power On/Off = 0,01V
2.7.5. = 5,15V
4.10.11. = 13.04V
12. InverterOn/Off = 0V
13. E-PWM = 0V
14. DET_5V = 0,01V

in powered on:
CP815 = 300V
1. Power On/Off = 0,76V
2.7.8. = 5,14V
4.10.11. = 13.01V
12. InverterOn/Off = 5.1V
13. E-PWM = 2.02V
14. DET_5V = 0,12V

[vinceroger69]

Re: Samsung LA32B350F no backlight

cp815 is that the maximum voltage it gets too as i just tested a working psu and i get roughly 390v when psu is on

[budm]

Re: Samsung LA32B350F no backlight

So now you longer get the 396VDC boosted Voltage? Without that the rest of the power supply and the circuits that require the boosted Voltage will not function.

[vinceroger69]

Re: Samsung LA32B350F no backlight

I dont see how his voltage readings listed below keep altering all the time
one minute the pfc voltage is good one minute its not

ok new measuremets (my input is 227V AC I am from EU):
in stand by:
CP815 = 304V
1. Power On/Off = 0,01V
2.7.5. = 5,15V
4.10.11. = 13.04V
12. InverterOn/Off = 0V
13. E-PWM = 0V
14. DET_5V = 0,01V

in powered on:
CP815 = 300V
1. Power On/Off = 0,76V
2.7.8. = 5,14V
4.10.11. = 13.01V
12. InverterOn/Off = 5.1V
13. E-PWM = 2.02V
14. DET_5V = 0,12V

[budm]

Re: Samsung LA32B350F no backlight

I know, I mention that about the DCV on the main cap to be that low in standby when the AC Input is at 327VAC and the cap Voltage is only 304VDC. It is either measurement error or the meter, etc.
I.E.:
2.7.5. = 5,15V
4.10.11. = 13.04V

It is hard to troubleshoot the problem with bad data.
The format of the report is also confusing.
Pin 2 is 5.15V pin = 7.5V?
Pin 4 is 13V pin = 10.11V?
Not the same format as used in post 39.
Hard for me to do any more helping at this point.
Need to get that Voltage on the main cap correct first by checking that main filter cap, solder joints, bridge rectifier, etc..

[vinceroger69]

Re: Samsung LA32B350F no backlight

I know im still learning myself but it does test your patience at times with bad data readings etc, its like when we have too ask more than once in diffrent threads for pictures etc of there boards we dont always have time too look on shopjimmy and upload them ourselves etc, also we dont always know the board/revision part number i think its stopping a lot of experienced members on here offering advice in my opion.

[attainteddragon]

Re: Samsung LA32B350F no backlight

this may be not be possible, but i was just wondering if there could be a template used to start a new thread. that way all the info to start off would be available from the beginning, outside of updated pictures and the like, but it could make things flow a little bit smoother.

just a thought.

[dskall]

Re: Samsung LA32B350F no backlight

Well I just made a text file so I can just copy and paste. Gets real tiresome asking for same info all the time.

[mrobo]

Re: Samsung LA32B350F no backlight

I know, I mention that about the DCV on the main cap to be that low in standby when the AC Input is at 327VAC and the cap Voltage is only 304VDC. It is either measurement error or the meter, etc.
I.E.:
2.7.5. = 5,15V
4.10.11. = 13.04V

It is hard to troubleshoot the problem with bad data.
The format of the report is also confusing.
Pin 2 is 5.15V pin = 7.5V?
Pin 4 is 13V pin = 10.11V?
Not the same format as used in post 39.
Hard for me to do any more helping at this point.
Need to get that Voltage on the main cap correct first by checking that main filter cap, solder joints, bridge rectifier, etc..

It was meant so:
pin2. pin7. pin5. = 5,15V
pin4. pin10. pin11. = 13.04V

[vinceroger69]

Re: Samsung LA32B350F no backlight

As budm says your next step now is you need to get that Voltage on the main cap correct first by checking that main filter cap, solder joints, bridge rectifier, etc and get it as close to 390v as you can when the set is powered on.

[budm]

Re: Samsung LA32B350F no backlight

It was meant so:
pin2. pin7. pin5. = 5,15V
pin4. pin10. pin11. = 13.04V

OK, that clears up the readings.

[mrobo]

Re: Samsung LA32B350F no backlight

Today I made measurements with other digital multimeter tool, with Metex M-3650D (putted new battery into)
I uploaded it in excel, I hope it is clearly now.
I measured all diodes in circuit with nothing bad found, some of them out of the circuit and measured with no problem found, like the
ZM801 .989 PN, 141 KOhm PN
in power circuit:
ZM804 .973 PN 135 KOhm PN
ZD804 .965 PN 135 KOhm PN
ZD803 .965 PN 131 KOhm PN
of course in NP all have open circuit
visually inspected the electro caps no problem found, measured in ohm if they charge and discharge in circuit and no problem found
some of them I changed even they seemed to be good (found recomendation in this badcaps forum with similar problem )
DP805 I have with number 31GF0927G should I change it?
Because Samsung SEUK Technical Support Service SVC Guide for No Power to Backlight caused by diode on IP Board.
I measured it and for me seems ok.

[vinceroger69]

Re: Samsung LA32B350F no backlight

you are getting some voltages im not 100% there all correct though and the maximum the pfc goes to is 308v with tv on that does seem low maybe budm has some ideas what to check/advise next

[budm]

Re: Samsung LA32B350F no backlight

So the DCV between the two legs of the main filter is lower than normal with 225VAC input so the bridge rectifier, connections, etc should be checked. You also do not have boosted Voltage when PS-ON is present. The 3 PFC Diodes I asked you to check in post 47 are good per your report. Need to get that cap Voltage correct first, Some how you were able to get the boosted Voltage in one of your post but not now so look for bad connections on solder joints.

[vinceroger69]

Re: Samsung LA32B350F no backlight

just saw this video and it looks like you have all the correct voltages seems odd if pfc is low?
https://www.youtube.com/watch?v=RL5-GtwypiY
so maybe watch this video and re check all your voltages as per this video as see if they match ok
https://www.youtube.com/watch?v=ocqnqmBxiqY this video is good regarding pfc at about 10 minutes in but please note he is on 110v i think
norcal does mention most voltage rails will run in standby but dont get full current ? untill pfc works

[attainteddragon]

Re: Samsung LA32B350F no backlight

just out of curiosity, have you bench tested the ps without anything hooked up?

[mrobo]

Re: Samsung LA32B350F no backlight

Need advice : I found two diodes on the other side of board, they measured results are strange to me, look at picture
DP802 = KDS184 24mV 26 Ohm both sides!!! (ok they are probably good they have low resistor connected paralel)
DP807 = KDS184 2mV 1.4 Ohm both sides!!! (ok they are probably good they have low resistor connected paralel)
compared to
ZP801 = Z02W6.8VY 534mV PN 25.5 KOhm, which is zener, but seems for me good
I have not much skill in desoldering smds, before I try could you confirm me to continue or search for problem elsewhere?
I dont know how to measure the mosfet, I post mmy results for QP802 = IPA60R600CP 6.1A 650V
tested like diode
pin 1 - 2 = 1726 mV NP
pin 1 - 3 = 1545 mV NP
pin 1 - 3 = 450mV PN
pin 3 - 2 = 485mV PN
pin 1-3 even 3-1 = 8.4 KOhm
could the mosfet bad?

[vinceroger69]

Re: Samsung LA32B350F no backlight

if your board has PFC IC (FAN 7530) i think it is i would check your getting all the correct volatges too it as for some reason the pfc is staying low