loopyloo (30-08-17)
With no load attached to the supply and using the series lamp, you could just put a nail in the fuse holder for testing. If the light comes on full brightness there's still a problem
loopyloo (30-08-17)
Well the series lamp lit then dimmed right off so I'll try the main board to see if it switches the PS fully on, but I'll check for 340v first.
Measuring off the mains cap it comes up to 320v so looking good so far.
Ok so I connected the main board completely and left the backlights disconnected.
At mains on the series lamp lights briefly then not glowing, I get the front red stby light and the mains cap sits at 340v.
Press on and the series lamp comes up slowly and stops at a dim glow (just orange), the stby light turns blue, the mains cap drops and sits at 250v.
5v good, 12v good, 24v good but no power at backlight connectors. Is that because the main board senses no connection ?
Last edited by loopyloo; 30-08-17 at 04:47 PM.
That sounds good to me, the low voltage likely due to losses in the series lamp but nothing obviously failing
Could be time to try powering up without the series lamp with everything connected
loopyloo (30-08-17)
FIXED !
TV now working well. The back is on. The screen now clean..
Thank you for the help once again.
Skepticist (30-08-17)
1 for 2 now
Good work
loopyloo (30-08-17)
The main thing to watch out for now is any overheating with a bus voltage a bit below what the PFC was creating (I'd say about 10% less voltage so maybe 10% or more extra heat in that heatsink from the 1 FET)
loopyloo (30-08-17)
Skepticist (30-08-17)
Well done, Loopylou and Skepticist!!
loopyloo (30-08-17),Skepticist (30-08-17)
A little follow up :
We set it up in the loungeroom two days ago.
This morning it was running for about an hour when it suddenly lost picture yet everything else was working. Didn't check if it was only backlights off.
Turned the TV off then back on and the picture returned.
Have to see how it goes over the next few days.
Last edited by loopyloo; 05-09-17 at 10:57 AM.
More sleuthing required
Could be just the backlights circuit being more sensitive to slightly lower HV bus voltage going by previous symptoms when using series lamp ?
These things are an endless source of entertainment even without any program showing lol
loopyloo (06-09-17)
Ok so the TV goes blank a couple of times per day.
It's the backlights turning off. Turn the TV off then back on again restores it.
It seems I'll have to have another look at it.
Well worth getting this one right, my son told me about youtube having 4k test videos and I have to say the picture it produces is stunning. 4k is so clear that objects, clouds, rippling water etc. tend to look 3 dimensional. Awesome. What's more, the wife is very impressed and that's a rare thing.
Last edited by loopyloo; 13-09-17 at 10:12 PM.
It's gotten a lot worse now.
Keeps turning off quite regularly. Have to put it out of service and have another look.
So just the LED backlights failing still?
Sounds like an overheating thing - got a can of that 'freezing spray' handy?
Yep got freezer spray.
I won't be looking at it until next week but What I'll do is first check to see if the main board is still giving the power on signal to the backlights (when it goes off) then I'll have to see if I can get a voltage measurement from the power supply.
Should be able to make use of the spray in there somewhere.
Hope the fault's not in the backlights themselves. I had them set to about half brightness.
Last edited by loopyloo; 14-09-17 at 10:54 PM.
Shouldn't be hard to locate the backlight controller (PWM most likely) - let's hope the chip ID is readable and take it from there with a datasheet in hand.
loopyloo (15-09-17)
The fact that it's getting worse also makes me think something is changing, like a capacitor or resistor deteriorating, a solder joint drying up or a widening crack somewhere, maybe can't rule out the video chip either.
Not sure if heat makes it go off. The misses went to turn it on yesterday and it went off after 5 mins, she then tried several times to get it to stay on but it was stubborn and kept turning off shortly after.
5 mins later I turned it on and it stayed on for an hour before it quit.
Last edited by loopyloo; 15-09-17 at 12:23 PM.
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