Celcus 48UHDSB-0/1 - intermittent shut down

[dailewis]

Hi,
I've got. Celcus TV in that shuts down usually after about 45 minutes. It can then be turned back on but then shuts down in between 2-5 minutes each time.

The backlights look like they're all lighting up however the screen when a picture is on it is very dim. I haven't stripped tv yet to check backlights with my tester.

I have pulled all caps from the board and tested them with my ESR meter and they all appear good on the cold side.

one thing to note is that when the tv powers up there is a high pitched whine and a faint crackling noise coming from the Vestel 17IPS20 power supply.

It appears to be near the transformer TR200.

I've also replaced all the F5404 diodes as a precaution.

Any pointers would be helpful, I'm determined not to swap this PSU out if I can fix it at board level :-)

Cheers

[dailewis]

Re: Celcus 48UHDSB-0/1 - intermittent shut down

I'm getting 88.6V at the output filter caps (56uF - 160V).
If I disconnect backlight, getting 140v on startup then it drops to 79.4V
When backlights disconnected the whining stops

[R_J]

Re: Celcus 48UHDSB-0/1 - intermittent shut down

I don't know the version of your power supply so post some pictures, I would suspect the small elec. caps. like C240 & C207

[dailewis]

Re: Celcus 48UHDSB-0/1 - intermittent shut down

just checked and D101 MUR460G is shorted fully both ways. Just ordered some from cpc farnell.

I'll update when they're fitted.

[budm]

Re: Celcus 48UHDSB-0/1 - intermittent shut down

Where is this D101 located on the board? Pictures of the board will help.
I cannot see how shorted diode will allow the TV to be working for 45 minutes then shutdown.

[R_J]

Re: Celcus 48UHDSB-0/1 - intermittent shut down

Looks like the diode is in the B+ line just after the PFC fet, so it was likely a low B+ condition allowing the tv to work for a short time.

[dailewis]

Re: Celcus 48UHDSB-0/1 - intermittent shut down

Here are the pics of the board

[budm]

Re: Celcus 48UHDSB-0/1 - intermittent shut down

So that means boosted PFC Voltage is not present if the PFC Diode shorted out and the circuit does not have have PFC Voltage shutdown either to keep the cost down

[dailewis]

Re: Celcus 48UHDSB-0/1 - intermittent shut down

Replaced Diode and running perfectly now😊
Thanks for the explanation of what was happening.

[budm]

Re: Celcus 48UHDSB-0/1 - intermittent shut down

Thanks for the follow-up on the repair.

[frica]

Re: Celcus 48UHDSB-0/1 - intermittent shut down

+1