Hi all I know theres alot of issues with these supplies and no backlight, today the symptoms of the issue with this one were the following:
No backlight
0v on Led output
Q502 and D504-Led output boost devices not shorted
0v on D303-D314 which are 6 diodes in parallel for Led output meaning Q301 transistor for Led output is not turning on enough or at all
Found only 330v across main caps meaning Pfc mosfet Q100 not turning on
Pfc controller U101 starts then shuts down Vcc drive voltage meaning issue is in the primary side
Things to check:
Q301 for S/C
Q101 for S/C note both these can blow and if their resistors fail open quick enough the mains fuse will not blow and Psu likely will start with no backlight
D506 for leakage current, this diode does not normally fail S/C but leaky acorss the cathode to anode so check that
What I found:
U300 check if its sending Vcc now I found it did but then shut down too meaning issue with either U101 or U300 or related parts
Checked U101 found low resistance across pins 1 and 3
Checked C127 (near U101) 50 ohms across it meaning theres a short acorss that cap, removed and checked however cap is fine out of circuit
Then checked C525 (under Q301) which is in parallel with C127 and both U101 and U300
C525 had lower resistance across it
Removed C525 and its shorted
Checked controllers again and low resistance gone
Replaced C525 which I believe is a 1uf 50v multilayer ceramic cap-MLCC stole one off a scrap IPS20 which is not worth fixing and replaced resistance still good
Put the Psu back into the Tv and the set now works. Hopefully help someone out, remember to check that cap if your Led section is totally dead with no output
Video coming tomorrow or Tuesday.
No backlight
0v on Led output
Q502 and D504-Led output boost devices not shorted
0v on D303-D314 which are 6 diodes in parallel for Led output meaning Q301 transistor for Led output is not turning on enough or at all
Found only 330v across main caps meaning Pfc mosfet Q100 not turning on
Pfc controller U101 starts then shuts down Vcc drive voltage meaning issue is in the primary side
Things to check:
Q301 for S/C
Q101 for S/C note both these can blow and if their resistors fail open quick enough the mains fuse will not blow and Psu likely will start with no backlight
D506 for leakage current, this diode does not normally fail S/C but leaky acorss the cathode to anode so check that
What I found:
U300 check if its sending Vcc now I found it did but then shut down too meaning issue with either U101 or U300 or related parts
Checked U101 found low resistance across pins 1 and 3
Checked C127 (near U101) 50 ohms across it meaning theres a short acorss that cap, removed and checked however cap is fine out of circuit
Then checked C525 (under Q301) which is in parallel with C127 and both U101 and U300
C525 had lower resistance across it
Removed C525 and its shorted
Checked controllers again and low resistance gone
Replaced C525 which I believe is a 1uf 50v multilayer ceramic cap-MLCC stole one off a scrap IPS20 which is not worth fixing and replaced resistance still good
Put the Psu back into the Tv and the set now works. Hopefully help someone out, remember to check that cap if your Led section is totally dead with no output
Video coming tomorrow or Tuesday.
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