Insignia NS-LCD19 no picture but has back light and sound

[1simtime]

When plugged in the amber LED flashes 8 times (pattern changes every time I plug it in). I have 5V and 12V.

When powered, LED turns green, after approx. 15 sec. the back light comes on and screen is white/grey. I have 5V ,12V,3V on/off and 3V dim. so P.S. seems to be working.

Buttons appear to work,I have sound and can hear when channels change. When I change inputs to AV1 I have sound.
When powered down LED flashes amber (random patterns) back light shuts off and LED is solid amber.

No parts appear bad or damaged, checked for bad solder joints. Only 5 leaded caps.I checked for shorts and used diode checker in area of cable to panel. I do not have an ESR meter and have not removed any parts to check, all in circuit so far.

Any ideas where to start ?(other than replace M.B.)
It sure be nice to have separate T-Con board

Thanks

[Dgtech]

Re: Insignia NS-LCD19 no picture but has back light and sound

Try another input. Which one are you using now? HDMI? Does it do the same with COAX or Composite?

[1simtime]

Re: Insignia NS-LCD19 no picture but has back light and sound

I used the coax for tv and yel/rd/wt rca for input 1 . I did not try hdmi or pc input.

Also the menu does not pop up ,but when I press the button I see a very faint shadow of the outline of the menu box.

[momaka]

Re: Insignia NS-LCD19 no picture but has back light and sound

Might be a bad t-con/panel board.

First make sure that all of the cables are plugged in and seated properly, though - especially that twisted multi-color strand in the second picture. This cable actually goes to the t-con/panel board, so if you follow it you will get to the t-con board (you will likely have to remove the power supply and video board to get to it). Once you get access to the t-con board, take some pictures and post them here.

In worst case scenario, one of the voltage rails may be shorted on the t-con board, but that's usually still repairable.

[1simtime]

Re: Insignia NS-LCD19 no picture but has back light and sound

I have already removed the P.S. , M.B. and mounting plate .I saw the back of the panel but no t-con board. I also checked all the cables .The cable goes from the M.B. to the panel.The twisted multi-colored cable goes to the buttons and the other larger black cable goes to the panel

[daimoku]

Re: Insignia NS-LCD19 no picture but has back light and sound

The tcon is located in the top middle part of the tv under a metal shield. You will see a cable known as the LVDS cable running from the main board to the tcon.

[daimoku]

Re: Insignia NS-LCD19 no picture but has back light and sound

Here's a pic of where the tcon is located (attached). This picture is from an Insignia NS-LCD32.

[1simtime]

Re: Insignia NS-LCD19 no picture but has back light and sound

I guess I did not look close enough last time .I found the T-con board! I didn't have much time to check it out . Visual looks good ,fuse good,o ohm res. good . I am open to ideas.

[momaka]

Re: Insignia NS-LCD19 no picture but has back light and sound

Good to see that you're one step ahead and have checked the fuse.
The next step would be to power on the TV with everything connected and see if power is actually coming to the fuse on the T-con board. Hopefully one of those test points on the top side of the T-con board is connected to that (check with your multimeter, though) so you can have an easier time taking the measurements.

If there is no voltage coming to the fuse, then it's probably a bad transistor or voltage regulator on the video/logic board that provides power to the T-con board.
If there is a voltage coming to the fuse, then the problem is most likely somewhere on the T-con board. To get further help on that, though, I'll need a clearer, more focused picture that captures the area of the LVDS connector plus the inductor, and maybe an inch or 2 to the right of the inductor.

[Scenic]

Re: Insignia NS-LCD19 no picture but has back light and sound

this really reminds me of this video...

http://www.youtube.com/watch?v=6bhEoUh0GV8

[1simtime]

Re: Insignia NS-LCD19 no picture but has back light and sound

Great video ! Thanks

I got 4.1V from gnd. to the fuse on the T-con.

After seeing my pictures, appears C30 is damaged.(not sure if I did it,cause I did not see it last night)I do not know the value of C30 .Any ideas on replacement? I think all 4 caps may be the same value I will have to remove them and check.
Also not sure what was on U5 but I cleaned it off. Looked like silver paint.

I may have just cracked the coating on C30. In pic. 3,4 top of the 4 caps in parallel 4.3V. bottom 0V which goes to U5 pin4. powered on U5 gnd to pin1,4=0V pins5,8 =2.99V. My test leads are too big to measure pins 2,3,6,7. I will work on that. Could U5 be the problem?

[Scenic]

Re: Insignia NS-LCD19 no picture but has back light and sound

looks like U1 got pretty hot (board discoloration)
also, you mentioned that you've cleaned the silver stuff off of U5.. but you didn't tell what it says on it

[ignore this sentence .. where's the BB-code for crossed out text?] 4.1V sounds pretty high.. 3.3V is a common value on LCDs up to around 22".[/ignore]
on the other hand.. if it's supposed to be 5V, it's pretty low.. hmmmm

edit: here's the datasheet for this LCD panel (Chi Mei M190A1-L02 19" 1440x900)


looking at the 3rd pic in post #11, the last 3 pins going to the fuse (the actual last pin is just for the connector shielding) are supposed to have 5V on them (VCC ; see page 12 in the PDF)
so it is indeed kinda low.. hmm.. something loading it up too much (shorted components?) !?

[1simtime]

Re: Insignia NS-LCD19 no picture but has back light and sound

U5 is marked " U1 D
ATO 8A"
M.B. U903 pin 1=1.24V pin2=2.49v pin3=4.18v
T-Con U1 pin1=0V pin2=4.11V pin3=2.49v
ALL MY READINGS ARE USING CHASSIS GROUND to the pins!(even my other posts also)
Should I be using different gnd ?

[momaka]

Re: Insignia NS-LCD19 no picture but has back light and sound

Wow, thanks for the great pictures. Makes troubleshooting a lot easier.

ALL MY READINGS ARE USING CHASSIS GROUND to the pins!(even my other posts also)
Should I be using different gnd ?

Nope, you're good with that.

Could U5 be the problem?

Not impossible but unlikely. Generally, it's not the ICs that fail, but rather the small ceramic caps (they usually short out). With that said, I would leave the ICs alone for now.

In pic. 3,4 top of the 4 caps in parallel 4.3V.

That's way too low. It should be 10V+. Something is definitely dragging it down. The fact that it's boosting to 4.71V, whereas the input to the T-con is 4.1V means that the circuit is actually working. You mentioned in post #3 that you can also see a faint outline of the menu, so that means that all of the ICs are indeed working fine. My guess would be that there's a shorted ceramic capacitor on one of the the secondary boosted voltage rails.

Basically the way T-con boards work is they take 5v in and then produce a main boosted voltage rail, usually 10V to 13V. This boosted voltage rail is then used to produce two other secondary boosted voltage rails, one usually negative (-5 to -10V) and another positive one (13V to 28V). These are the secondary voltage rails I was talking about above.

On your T-con board, the main boosted voltage rail starts at the cathode of diode D3 (the side marked with the white stripe on D3). It's controlled by U6 (FP5138).

At this point, I don't think we need to do any troubleshooting on the main boosted voltage rail (C30 aside). Perhaps, just measure resistance between the main boosted voltage rail and ground, just to make sure it's not shorted (if it's less than 50 Ohms, let me know what reading you get).
Also, here is the datasheet for U6 anyways as it might give you a better understanding of what some of the components on the T-con do (the first sample circuit on page 13 seems to be very close to what's on your T-con):


Now, unfortunately U6 is not one of those "smart" ICs that also control the secondary boosted voltage rails (like the MAX1748, for example), so that's making it a little harder telling where they are located. I'm guessing it's those components to the right of L1.
So, I think a good point to start is to check all of the ceramic capacitors to the right of inductor L1 (using the 4th picture as a reference). That is, measure resistance across C20, C23, C24, C25 and the rest of the ceramic capacitors there. If any of them show under 30 Ohms resistance, let me know what readings you got for them.

Also, if possible, please take some resistance measurements across the various pins of D1. I'm trying to figure out what it does, and I'm almost certain that the secondary boosted voltage rails are in that area. Basically, what I'm looking for is a circuit similar to the one on page 10 of the Max1748 datasheet found here.

After seeing my pictures, appears C30 is damaged... I do not know the value of C30 .Any ideas on replacement?

The way I do it is I just take another ceramic cap of the same size from a junk board and use that. I know it's not an ideal solution but it works (fixed and extensively tested two LCD monitors that way - both had white screen problems like yours, too).

Sorry for not keeping the post shorter. Not sure how to explain it better.

[1simtime]

Re: Insignia NS-LCD19 no picture but has back light and sound

I didn't give up ,just limited on time.I used a different meter because the lcd display is hard to read on my 24 year old DMM.
ALL ON T-CON BOARD
Caps measure from 55K-500K Ohms (in circuit).
voltage at fuse =4.96V--C29,30,31,32 =4.56V--U1 pin 1=0V, 2=4.94V, 3=2.49V
U6 pin 1=.18V, 2=.076V, 3=4.949V, 4=.24V, 5=.85V, 6=.35V, 7,8=0V
C27=1V , C24=3.56V , C20,23=4.94V , C25=3.52V , C34,35=4.94V
C17=2.79V , C4=2.49V
D3 anode= 4.94V ,cathode =4.56V
R122,R119,R116,R121,R55 all =0 Ohm (not marked)
D1 pin1 (off C20).004V, 2=.005V , 3=3.54V , 4=4.06V , 5=4.56V , 6=.004V
I noticed with input to TV I see faint colored vertical lines. still have sound

[1simtime]

Re: Insignia NS-LCD19 no picture but has back light and sound

I updated the picture with voltages (hope they show up)
I removed C29=10.4uF,30=6.36uF,31=10.9uF and 32=10.9uF.
I will try to find replacement for C30 and reinstall all 4

[momaka]

Re: Insignia NS-LCD19 no picture but has back light and sound

I removed C29=10.4uF,30=6.36uF,31=10.9uF and 32=10.9uF.
I will try to find replacement for C30 and reinstall all 4

Sounds good.

I noticed with input to TV I see faint colored vertical lines. still have sound

Right. That's because the t-con is likely working, but again, the voltage on the main boosted voltage rail (which is basically anything that is connected to the cathode of D3) is too low. Needs to be at least 10v.

Caps measure from 55K-500K Ohms (in circuit).

That means none are shorted - that's good.

Check diodes D2 and D3. You can use either diode check function on your multimeter or 2000 Ohm scale. Put black (-) probe on cathode and red (+) probe on anode. Record the numbers you get on your multimeter. Now reverse the probes and record the numbers again. Let me know what they are.

Also, if you could do something similar for diode D1, that would be great because I've been looking for a datasheet for it but just can't find any. Basically, put red (+) probe on one pin (say, pin 1 for example) and then measure resistance to all of the other pins (using either 2000 Ohm scale or diode test function). Now reverse the probes and repeat. Then move to pin 2 and repeat the last two steps above.
I know that's a lot of work, and I apologize for that, but the voltage readings on D1 simply are not enough to determine its internal schematic, and D1 has a key role in the secondary boosted voltage rails, which is where the problem likely is.

Lastly, could you provide another picture of the t-con board that covers exactly the opposite side of IMG-3973 (if it's not a problem, of course). I think there are some test points on there that may be helpful.

[1simtime]

Re: Insignia NS-LCD19 no picture but has back light and sound

Replaced C29=9.4uF V? and C30=9.3uF V? and screen flashed and Q4 smoked.
I checked for shorts and solder balls before I powered up so I don't know why Q4 went. Q4 is marked NAH3.
Q4 =top-bottom left=2.2 Ohm/top-bottom right =short
U1 1-2=2.2 Ohm
C35,C33,C3,C1,C2=2.2 Ohm

[momaka]

Re: Insignia NS-LCD19 no picture but has back light and sound

If you carefully read my earlier posts, you would have understood that the fault is somewhere else and not C30. Replacing C30 was a good idea, but like I said, this alone would not fix the problem, and with that said, you should have refrained from powering on the TV.

These t-con boards are tricky, and the key to fixing them is to first get a basic understanding of the circuit (or at least get a general idea of how some of the components are connected) before changing anything and applying power. This is why I asked for resistance measurements on D1, D2, and D3. At this point, though, since Q4 smoked, there are more important things to check first...

C35,C33,C3,C1,C2=2.2 Ohm

2.2 Ohms is pretty much a short circuit.
This short across C1, C2, and C3 indicates the main 5v supply rail is shorted. Need to isolate the area where the short is first, then find the shorted component before doing anything else. At this point - do not apply power to the TV anymore, unless you want more burned components.

To narrow down where the short is, first remove R67, then check resistance across either C1, C2, or C3 (doesn't matter which, they are all connected to each other). Make sure the LVDS connector to the TV's video/logic is disconnected, though.
- If the 2.2 Ohm resistance is gone, likely one of the following components may be bad: Q4, C20, C23, D3. Check D3 and measure resistance across C20 and C23, but don't remove anything if you get to this point, though. Just let me know if/when you do.
- If the 2.2 Ohm resistance is still there after removing R67, then remove R4, then check resistance again. If you still see 2.2 Ohms, carefully remove F1 and check resistance again. Let me know what resistance you get.

I checked for shorts and solder balls before I powered up so I don't know why Q4 went. Q4 is marked NAH3.

Can't seem to find exact datasheet for it, but according to the FP5138 (U6) datasheet, Q4 should be either a NPN transistor or N-channel MOSFET.
The closest thing I can find is for the string "AH", which yields a BCX70H NPN general purpose transistor (using the SMD code book).

[1simtime]

Re: Insignia NS-LCD19 no picture but has back light and sound

Removed R67 short is gone at C1.
C34, C35 still 2.2 Ohms.
Q4 top leg to bottom left =15 Ohms
Q4Top to bottom right(goes to GND) =2.2 Ohms