Toshiba 40L1533DB - Dead repaired - PSU Noise

[pic_whiz]

Hi All,

I've just repaired the Vestel 17IPS71 PSU in this set. Diode D20 was O/C. This brought the set back to life however no backlight.

Discovered resistor divider connected to OVP on the MP3394S driver had failed, both R107(390K) and R106(240K) were O/C and slightly burnt.

Replaced both resistors, backlight and set now working.

The issue I now have is switching noise/whine that is very audible. What would cause this? PSU is louder when operating but noise is present in both standby/on.

Many Thanks,

Matt

[nomoresonys]

Re: Toshiba 40L1533DB - Dead repaired - PSU Noise

Heat the caps with a hairdryer, see if it gets quieter.

[pic_whiz]

Re: Toshiba 40L1533DB - Dead repaired - PSU Noise

Thanks, seems the heat doesn't affect it.

I've got a spare 17IPS71 coming today so I will test this as a comparison.

Cheers,

Matt

[PontyPCs]

Re: Toshiba 40L1533DB - Dead repaired - PSU Noise

Sounds like a choke squealing,check all chokes for dry joints including the Backlight pulse transformer, also check the diode for leakage connected to the pulse transformer.

[pic_whiz]

Re: Toshiba 40L1533DB - Dead repaired - PSU Noise

Just an update.

Replacement PSU arrived, much quieter.

Tried swapping both transformers, diode on LED driver, various caps to no avail. I have DSO traces of both to compare, so there's something going on, see attachments. This trace is from the LED driver diode from both good and bad boards.


Cheers,

Matt