Emerson EWL20S5 double image on screen

[DakotaKid]

This TV was given to me and I plan to fix it and put in my garage to watch while i work out there. It's a 20" LCD, DVD quality picture but not HD and not widescreen. It has a single mainboard with everything except inverter circuitry and then a separate inverter board. The mainboard appears cheaply made but surprisingly well labeled. This board must also be used in a combo TV /DVD unit as it has markings for those components (not installed) as well. No apparent burns or damage on either side of the board.

Symptom: TV will power on and show blurry ghost double image, one on top half of screen and one on bottom half. After it warms up the image becomes very clear but still displayed once at top half and once on bottom half. For instance, blue background with "VIDEO 2" displayed twice when no input signal is attached. Caps around power supply section are not bulging or leaking but are of a brand I have never heard of and I assume very cheap and prone to failure. The voltages are fairly close to expected values EXCEPT the panel 10.8V supply is actually 12.7V. The 5V is 4.86V.

I am attaching a picture of the board, a closeup of the power supply section. I downloaded a schematic at elektrotanya, excerpt attached relevant to mainboard.

I did find a discrepancy that I cannot reconcile and would appreciate any help. The voltages at Q503 on the schematic vs actuals are B=11V (actual 13.25V), C=13.6V (actual 19.25V), E=10.8V (actual 12.7V). Q503 is a KTD2059 transistor. Capacitor C503 (220uf/16v) and diode D504 are in the same circuit leg.

Hope this all makes sense to someone out there that can help.

Thanks in advance.
DK

[DakotaKid]

Re: Emerson EWL20S5 double image on screen

Anyone help with this one? Thanks.

[retiredcaps]

Re: Emerson EWL20S5 double image on screen

I assume this TV has a t-con board? If yes, have you tried cleaning and reseating all the connections originating from the board?

[selldoor]

Re: Emerson EWL20S5 double image on screen

Didnt want to be the one to say it, but your pictures are poor, It is really all we have to work on. They should look like these:
Examples of what is needed
https://www.badcaps.net/forum/attach...1&d=1290283049

https://www.badcaps.net/forum/attach...7&d=1280167246

[DakotaKid]

Re: Emerson EWL20S5 double image on screen

Didnt want to be the one to say it, but your pictures are poor, It is really all we have to work on.

No offense taken but it's all I had at the time and they were (a little) better than nothing. Since there is no evidence of bulging caps or burnt components I thought the schematic I attached and the actual voltage readings that I gave would be more helpful.

I will clean the contacts leading to the LCD panel and will report back but I am still confused about the voltage readings around Q503 and the 12.7V instead of 10.8V at that test point.

Thanks all.
DK

[budm]

Re: Emerson EWL20S5 double image on screen

"The voltages at Q503 on the schematic vs actuals are B=11V (actual 13.25V), C=13.6V (actual 19.25V), E=10.8V (actual 12.7V). Q503 is a KTD2059 transistor. Capacitor C503 (220uf/16v) and diode D504 are in the same circuit leg. "

Q503 is setup as high current pass transistor Emitter follower with the regulated (TL421 Ref Diode) Base voltage to ground that should be 11.4V to get 10.8V (11.4v – 0.6v (Base-Emitter junction Vbe) out at the Emitter.
Right now the Base Voltage to ground is 13.25V, so minus 0.6v, you will get 12.65V as you have measured.
So the problem can be the 2.5v Ref Diode D505 is bad or the voltage divider resistor network R514, R516 (I left out R515 because it is a jumper) are out off value.
From my calculation to what you should get at the Emitter of Q503, it should be 108v as designed.
Vo = Vref(1+ R514/R516)
Since Vref is 2.5V, then Vo = 2.5(1+10k/3k) = 10.833V.

One thing that bothers me as far as the accuracy of the voltage labeling is not right.
If you look at D636, the output that goes to the output pin is labeled with +40v, but this same voltage also goes to Collector of Q504, and it is labeled as 36.7V, so I am not sure what to trust. You may have to verify a bunch of voltages as labeled and as measured.

[DakotaKid]

Re: Emerson EWL20S5 double image on screen

Thanks a lot budm. This helps me understand and begins to explain. The schematic pdf I uploaded in the OP had an addendum page that listed changes to R514 (6.8K) and R516 (1.6K) so if Vref is 2.5V then Vo becomes 2.5 (1+6.8k/1.6k) = 13.125V which is near (13.25V) what I read at that point. Furthermore, version "C" added four 10 Ohm resistors in series between the middle legs of Q503 and Q401 (on the 22V inverter circuit). I found and added the board diagram to the pdf that shows those four resistors near where Q504 is. Since the schematic published didn't have the updated components in it I guess it is possible that the expected voltages all change too...including the 10.8V that is reading closer to 13.7V. I will take the readings that you highlighted and post back here.

Again...thanks for your assistance.

DK

[budm]

Re: Emerson EWL20S5 double image on screen

Can you also show the whole back of the TV as how the boards are connected together and the picture of the LCD panel assembly?

[DakotaKid]

Re: Emerson EWL20S5 double image on screen

Per your diagram:
AL +13 reads 12.8V
Panel -6V reads -5.98V
Panel +25 reads 23.3V
Panel +10.8V reads 12.7V

Protect-1 reads 3.3V as expected from Q507

btw, this "double image" problem is common on this TV per google search but I haven't found anyone who actually solved it. I removed the LCD ribbon cables from the mainboard to the T-con and reseated them and it had no effect. Also, while the TV was operating I slightly flexed the ribbons at the LCD panel and nothing changed so they seem to be attached securely. I will put up a picture showing all of the connections soon.

[budm]

Re: Emerson EWL20S5 double image on screen

You may want to try cooling using a can of compressed air duster upside down to get cold sray on the board on the LCD panel, and also hairdryer to see if it has affect on the pictures.

[selldoor]

Re: Emerson EWL20S5 double image on screen

I have just been looking at the full version of the service manual.
It is not encouraging that the first items relate to instructions on removing/
replacing the video chip. Leads me to think there is a known problem and
either the chip needs replacing or a new board.
The second section however tells you how to set up the ordinary remote control to turn it into a service menu control. It may be that by adjusting some of the settings you could stop it splitting.

[DakotaKid]

Re: Emerson EWL20S5 double image on screen

I have just been looking at the full version of the service manual.
It is not encouraging that the first items relate to instructions on removing/
replacing the video chip. Leads me to think there is a known problem and
either the chip needs replacing or a new board.
The second section however tells you how to set up the ordinary remote control to turn it into a service menu control. It may be that by adjusting some of the settings you could stop it splitting.

I also thought that was a bit alarming to see that section dedicated to replacing the SMD video chip. I saw the part about the service menu but unfortunately I don't have an original remote. The TV is acting odd when playing a movie, as if something isn't responding quickly enough. It is sort of like watching slow motion frame advance where the screen blurs because it seems it can't keep up with displaying the changing input signal, like something isn't switching fast enough. Not sure if that is the video chip, the T-con or the actual display. And heck, it could all go back to voltage problems from bad caps or regulator I suppose. I still wonder about that 12.7V instead of 10.8V output in the power/regulator transistor section.

Maybe this thing belongs on CL for the next guy to take a shot at!! LOL.