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-   -   Philips 234e problem (https://www.badcaps.net/forum/showthread.php?t=78155)

dicky96 08-06-2019 10:45 AM

Re: Philips 234e problem
 
I'll check for numbers on the panel.

So you think there will be the VGH + 15V to + 20V, which is generated by L2 that I removed, and also a +12V as well?

If the +12V has a short abd it iis derived from the VGH then that could explain the symptoms I'll look to see if I can find anything. I don't recall seeing a 4th inductor anywhere

R_J 08-06-2019 10:51 AM

Re: Philips 234e problem
 
There in only one +5 volt supply on the cable between the main an tcon correct? so the other voltages must be generated on the tcon board
It seems a bit odd that if there is something drawing so much current on the tcon board it does'nt blow the fuse an the tcon.
Did you ever try supplying +5 volts from a bench supply just to the panel and see if you had the other voltages?

dicky96 08-06-2019 01:00 PM

Re: Philips 234e problem
 
Yes as far as I have determined there is only one +5V on the LVDS, but I will check again now I stopped the chirping with the LVDS connected.

So Yes the other voltages must be developed on the TCON. I can see three inductors, L3 generates 1.8V, L1 generates 5V (which seems a bit odd as we already have a 5V supply).

L2 I don't know what it should generate because the power supply chirps when it is fitted (but I have seen anything from 3.5V to 7V on it. But I will assume it is a high voltage like 15V to 20V

I can only assume the fuse on the TCON does not blow because the supply cuts out (chirps) first

No I didn't try supplying 5V to the panel PCB from my bench supply, I will try that next, with L2 fitted

I'll also try to get my multimeter in series with L2 and measure the current, I should be able to do that by soldering some 'legs' to it, or soldering a low value sense resistor in series and measuring across that.


Cheers

dicky96 08-07-2019 08:29 AM

Re: Philips 234e problem
 
1 Attachment(s)
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. https://youtu.be/N6-i57vSvK4

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. :why:

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.

dicky96 08-07-2019 12:56 PM

Re: Philips 234e problem
 
I suppose I could try replacing SM4043 - they are cheap to buy

dicky96 08-13-2019 11:42 AM

Re: Philips 234e problem
 
I ordered some SM4043 - let's see what happens when they arrive.....

glory68 11-10-2019 06:01 AM

Re: Philips 234e problem
 
Hello! What is the result after replacing SM4043? On my T-con exactly the same fault


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