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Old 08-07-2019, 08:29 AM   #24
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Join Date: Mar 2017
City & State: Sunny Gran Canaria
My Country: Spain
Line Voltage: 220V 50Hz
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Posts: 904
Default Re: Philips 234e problem

Panel number pics attached.

OK so I checked if I could see any other voltages supplied on the LVDS cable but couldn't, though 3.3V was present so I wasn't sure about that.

So I disconnected LVDS and used my bench PSU to power the panel edge PCB with 5V

Without L2 fitted I get a steady load of about 220mA and all the voltages I could see on the panel PCB with LVDS were still present (1.8V on L3, 5V on L1) and 3.3V and 12V though I'm not certain where those originate but they are from somewhere on board.

When I fitted L2 I get the chirping noise but it is now a constant chirp-chirp-chirp.... not in bursts of 4-5 chirps like before (so it the sound was coming from the panel edge PCB not the main PCB - my hearing is not very good to be honest) and I have 7V on L2

The current meter on my bench PSU was jumping up and down rapidly with each chirp so I can't say what the current draw was

There is no short from L2 to ground, and in fact it sits at 7V, so this is more like a zener or some other device breaking down on that voltage rail

I did wonder what would be the symptoms if I had a shorted turn in L2. As it is the same value component as L3 I swapped them round. I still get 1.8V on L3, and the chirping starts when I replaced L2 with the other inductor.

I then decided to use my dual bench supply to power the main board with 19V (so the back lights come on) and power the panel PCB with 5V with the LVDS disconnected to see what if anything i could see on the screen

This video is the results of that test.

I don't much like the look of it, truth be known. That purple vertical line slowly fades away to black after a minute or so once the 5V is switched off.

So the problem does seem to be that something is overloading the supply rail from L2 once it tries to go above 7V, but it's not a 'common or garden' short.

That's as far as I can get with this, I'm out of ideas apart from maybe removing L2 again and trying to drive that rail above 7V.
Attached Images
File Type: jpg 20190807_133020.jpg (455.8 KB, 5 views)

Last edited by dicky96; 08-07-2019 at 08:34 AM..
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