Philips 37PFL9604/H12 : backlight will switch off after some time on

oobabeloo
Gepost maandag 10 september 2018 20:14:09

Hi,

My TV (Philips 37PFL9604, chassis Q549.2LE) has an annoying backlight issue since a few days.

It will power up flawlessly but, after a certain amount of time, the backlight will switch off for a second, then switch on again. It will happen a few time until the screen goes black totally.

When the backlights are on, I cannot see any dimming or artefact on the screen, thus I would not bet on a CCFL issue. The TV has been used (display on) for a bit more than 5000hours.

I used a flashlight to check that the image was still present and it was the case and I also changed the 22µf and 47µf caps connected to the backlight.

Might be worth mentionning, the ambilight will stay on when the backlight switch on and off.

Is there some other components I should have changed or some other checks I should have done ? I tried to reduce the contrast and since then, the backlight issue didn't appear back (but the display is terrible !)

I must say that I previously had another issue with the inverted/psu card (DPS-298CPA) some months ago: an annoying click could be heared after being on for a few minutes (without any backlight issue a that time). Changing the IC601 and all mosfets cured it.

Thanks for your help

joe-joe
Gepost dinsdag 11 september 2018 16:19:55

send PM

smd
Gepost dinsdag 11 september 2018 18:20:11

Probably this is an CCFL backlight panel. Check transformer, capacitors or lamps itself

oobabeloo
Gepost dinsdag 11 september 2018 19:14:59

Op 11 september 2018 16:19:55 schreef joe-joe:
send PM

thanks joe, but I cannot see any pm.

oobabeloo
Gepost dinsdag 11 september 2018 19:17:09

Op 11 september 2018 18:20:11 schreef smd:
Probably this is an CCFL backlight panel. Check transformer, capacitors or lamps itself

thanks for your message.

HT ceramic caps were changed, I haven't checked the transformer yet (I need to find the valued to be checked). Should I need to big electrolytic cap just next to the mosfets too ?

I have read on this forum that when CCFL age, the HT caps might need to be doubled (parallel), does it apply here ?

Also, 5000hours does not seem to be a lot for CCFL tubes, does it ?

Shiptronic

Overleden

Gepost dinsdag 11 september 2018 19:18:30

Op 11 september 2018 19:14:59 schreef oobabeloo:
[...]
thanks joe, but I cannot see any pm.

Click on name en you wil see an e-mail adres.

Wie de vraag stelt, zal met het antwoord moeten leren leven.
oobabeloo
Gepost dinsdag 11 september 2018 19:21:12

Op 11 september 2018 19:18:30 schreef Shiptronic:
[...]

Click on name en you wil see an e-mail adres.

thanks, I was looking for a forum PM feature.

oobabeloo
Gepost vrijdag 14 september 2018 23:16:26

joe-joe is offering to sell a spare PSU.

is there anything I could try on mine to solve the backlight issue ?

smd
Gepost zaterdag 15 september 2018 19:00:42

In those cases it could be more than you think. CCFL lamp broken, test all CCFLs separate. 5000 Hours can be a lot when al lamps are running "overdriven" and mercury starved are. Also HV transformer can get sparking or driver. You need to divide problem. Sometimes I use a standard fluorescent tube for example 18W or 13W version to check if problem is in the driver or lamps.

oobabeloo
Gepost zondag 16 september 2018 14:38:16

Hello, I don't have the proper equipment to test the CCFL.
Can you elaborate a bit more on how you test the inverter with a fluorescent tube ? Also, by driver, do you mean the high voltage part of the PSU (it has an integrated inverted in this model) ?

smd
Gepost zondag 16 september 2018 18:55:28

Instead of connecting pink and white wire to powersupply HV output, you connect a fluorescent tube.
After reading about capacitors again: did you installed correct capacitance of capacitors??

oobabeloo
Gepost zondag 16 september 2018 18:59:28

Sure, I did.
And I changed them after having issue with the backlight.

oobabeloo
Gepost dinsdag 18 september 2018 07:57:36

I used 33 and 47 microfarads, I made a mistake in the first post. Note that I had issue with the backlight before changing these caps.

oobabeloo
Gepost zaterdag 22 september 2018 11:31:15

I swapped the IC601 with another one and the TV is working fine since then.
Could it be that the first one was faulty ?

smd
Gepost maandag 24 september 2018 18:50:20

It is most likely that original were faulty