Vizio E65x-C2 question about Gamma

[DXseekerMO]

Maybe the end of the road

I removed the source driver board covers (such fun) so I could take a closer look. I came up with a divide and test strategy starting with all cables hooked up, testing at the t-con VCOM test point

First I detached the left driver board from the left center driver board, short still exists

Next I detached the right driver board from the right center driver board, short still exists

Next I detached the left FFC cable from the t-con, short still exists

Next I re-attached the left FFC cable and detached the right, short still exists

Lastly I detached the left FFC cable from the t-con, open line.

Budm, I have concluded for a short to exist in the fashion tested does indicate a failed panel, namely a short somewhere upon the panel in the VCOM circuit. Would you draw the same conclusion?

[DXseekerMO]

Pronouncement of Death

A further re-check of VCOM voltage at the t-con, FFC's unhooked reveals about 6.8v

This TV was pronounced dead at 16:20 hours, on this thirty first day of October 2018 from an apparent short upon the panel itself, namely in the VCOM circuit.

If anyone thinks I'm missing something please let me know, but the short is too common to not be the panel. I can't isolate it any further, methinks.

[budwich]

Re: Vizio E65x-C2 question about Gamma

perhaps so... but you should be able to trace the vcom circuit going to the bottom edge boards and perhaps find any bad capacitors that might be replaceable.

[DXseekerMO]

Re: Vizio E65x-C2 question about Gamma

Right on...I am finding VCOM A and B test points on the buffer boards but nothing marked VCOM by itself. I'll keep looking and test from there.

[budm]

Re: Vizio E65x-C2 question about Gamma

Can I see some good clear pictures?

[budwich]

Re: Vizio E65x-C2 question about Gamma

Right on...I am finding VCOM A and B test points on the buffer boards but nothing marked VCOM by itself. I'll keep looking and test from there.

you know where the vcom test point is on the tcon.... measure / meter trace it to the tcon / panel cable... count the pins and look on the driver boards there after.

[DXseekerMO]

Re: Vizio E65x-C2 question about Gamma

OK the trace associated with VCOM appears to have 2 caps in circuit on the left driver board marked C104 and C304 and 2 caps marked C404 and C604 on the left center driver board. Likewise the VCOM circuit on the right center driver board has caps marked C704 and C904 and C1004 and C1204 on the right driver board.

All of these caps listed above indicate short. Furthermore it appears none of the other caps on any of the driver boards test short.

There are long and short hash marks near each of the driver tabs that appear to relate to long and short hash marks at the FFC connector.

Since this is a common circuit, if one of these caps is shorted it will make them all appear shorted because they all use the same circuit in the panel?

If so, it looks like I'm removing each of these caps until the short goes away? If I have to remove all of them to clear the short then the panel itself is shorted?

[budwich]

Re: Vizio E65x-C2 question about Gamma

before you get "soldery", isolate the bottom driver boards by disconnecting the interconnecting ribbon between them, then check the caps again. Likely you don't have to worry about the outer boards / drivers... hopefully.

further, in your first picture, c101 and c104 seem offset possibly... not sure if that would cause any issue but maybe if they aren't making good connection, then it might have "strained" other caps in the "parallel" to take more current than expected.... or something like that ... :-)

[DXseekerMO]

Re: Vizio E65x-C2 question about Gamma

The testing for shorted caps was done with the interconnecting ribbons detached.

[budm]

Re: Vizio E65x-C2 question about Gamma

Lots of caps on those boards are connected in parallel to get more capacitance.
You just have to start removing the suspected shorted cap until the shorts go away, the shorts can also be from IC's.

[DXseekerMO]

Re: Vizio E65x-C2 question about Gamma

I haven't checked the IC's yet....I will pull numbers and spec sheets (if I can find them) and see what comes up. Should I be finding ground pins and probe them while dragging the other pins to see if internally shorted? Should I check all pins for continuity to chassis ground as well?

[budwich]

Re: Vizio E65x-C2 question about Gamma

The testing for shorted caps was done with the interconnecting ribbons detached.

maybe... but picture 2 shows the cable still installed.

[DXseekerMO]

Re: Vizio E65x-C2 question about Gamma

Good catch, the ribbon cable is detached from the other board.

[DXseekerMO]

Re: Vizio E65x-C2 question about Gamma

The driver boards have three IC's on them, two 14-PIN G1564 quadruple rail to rail amplifiers near the outside of the left and right driver boards and one 8-PIN 25X40CLNIG winbond flash memory near the inboard right center driver board.

Pin arrangements:

G1564:
1....VOUT A.......... 14....VOUT D
2....VIN A-........... 13....VIN D-
3....VIN A+.......... 12....VIN D+
4....VCC.............. 11.... VSS
5....VIN B+.......... 10....VIN C+
6....VIN B-........... 9......VIN C-
7....VOUT B.......... 8......VOUT C

25X40CLNIG

1..../CS............... 8.... VCC
2....DO (IO)......... 7.... /HOLD
3..../WD.............. 6.... CLK
4....GND.............. 5.... DI (IO)

On both G1564's PIN 11, VSS shows directly shorted to chassis ground.

On the 25X40CLNIG the only pin showing a direct path to ground is pin 4 as expected. None of the other pins are shorted to chassis ground or to the ground pin itself.

[budm]

Re: Vizio E65x-C2 question about Gamma

The VCC pin of the IC will have filter cap (MLCC) connected between the VCC pin and GND so the short circuit will be either cap or internal shorts, or both (very rare), it is easier to remove the cap first than the IC.

[DXseekerMO]

VCOM no longer shorted directly to ground????

After more testing something interesting has happened. VCOM is no longer directly shorted to ground....and neither are those capacitors.

I noticed this change of state while testing a few more things, so I hooked up both FFC's one at a time and tested at the t-con VCOM test point, reference chassis ground as before and the reading is now 586 ohms. Furthermore, when I test the caps referenced earlier one side is direct to ground and the other is also now 586 ohms.

This change of state with good working equipment has to eliminate those caps as suspect since they all changed state and now read the same. The only thing I can think of is by probing those IC's, maybe the low current/voltage caused the IC to change state?

I am 100% sure my test equipment is working right, and I am 100% certain VCOM was once reading direct short to ground. I'm also 100% sure those caps were reading shorted too, and I am clueless as to how this happened!

[DXseekerMO]

Narrowed down to the right source driver board

I went back to re-check my readings and now something else has come to light. When I press on the right (outer) source driver board the amount of resistance at VCOM changes. When I repeat the test on the other 3 boards the resistance does not change. Any flexing of that board in any place causes fluctuations in the VCOM resistance reading. All of the previously mentioned caps on all boards change resistance as well. That means they are all good, maybe save for the XR2 board.

[DXseekerMO]

!!!!!!!we have a picture!!!!!!!

Ok, so the TV now has a viewable picture!!!!!

I detached the XR2 board from the chassis and held it in such a position I could flex only the flat cables that go from the board to the display. Mercifully the resistance at VCOM remained constant when I did this. I felt this eliminated those and bonding issues from the suspect list.

After putting the board back in place I continued to press on areas of the XR2 board with my finger and narrowed down significant ohms changes when pressing near IC UD01, so I grabbed my plastic pick and got real specific where I pressed and flexed the board.

Next I backed the board in such a way it couldn't flex and continued to press on components in this area. After this the ohms reading increased to over 1000 and pressing seemed to affect ohms readings a lot less. While they were not constant, the variance was only about 50-100 ohms.

At this point I decided to re-connect all the XR boards, plug it in and give it a try. Sure enough there is now a contrast correct picture. I didn't try it for long since I know there's a bad connection, but for Pete's sake....WE HAVE A PICTURE!

The way I was flexing the boards tells me something has to be loose on the board in that area, be it a bad solder joint or something. As far as I can tell the board is not cracked. There were no vertical or horizontal lines displayed on the screen and on-screen text is clear!

What do you all think? I must have pressed something hard enough to temporarily restore a connection? This sounds like a re-flow job is coming on all components in that area. I thought about turning it on and flexing the board to look for arcing.....but I don't think this is a good idea?

I suppose it could also be a shorted cap in that area broke/came apart and this cleared the short?

[budwich]

Re: Vizio E65x-C2 question about Gamma

guess its "death" was premature.

[DXseekerMO]

Re: Vizio E65x-C2 question about Gamma

guess its "death" was premature.

It appears there is that chance!

Interestingly enough, VCOM is now reading open line and no amount of flexing seems to change that. There has to be a shorted component on the XR2 board that came apart, but I'll be darned if I can see which one it is.

Pin 11 of that G1564 IC is still showing short to ground.

Would anyone have an inclination of which ones to check?