Vizio E65x-C2 question about Gamma

[DXseekerMO]

Re: Vizio E65x-C2 question about Gamma

I will measure the test points and report this evening. Any guess as to the normal voltage range without the spec sheet?

[budwich]

Re: Vizio E65x-C2 question about Gamma

I think if you are lucky and search on "gamma voltages", you will find some info... for other chips which may or may not be valid but certainly can't hurt.

[DXseekerMO]

Re: Vizio E65x-C2 question about Gamma

For now I'm going to leave the TV open but push on this one for tonight, unless someone happens to find a spec sheet. I tried with what I know, but no luck.

While researching as budwich suggested I ran across this video:

https://www.youtube.com/watch?v=batV1Mm0S9U

Interestingly enough the TV of which the video is the subject had a bad AS-15 gamma chip. I caught something it did, going from solarized to negative, and this is exactly what this Vizio is doing.

I'm going to go pick up some freeze spray and give that a go on those chips, and see if there's a change of picture state. If there is, and if specs can't be found that will be reason enough in my eyes to order the t-con without knowing gamma voltage specs. In my eyes if the chip is good there should be no change of picture state from temperature manipulation.

I was trained as a Master Auto Technician, now with 30 years of experience. From this I've learned in all things there is an answer, one of which isn't throwing parts at something to diagnose it. For me I have to have a reason to install a part. TV and car repairs can both have info not available, and that's when we REALLY find out who's smarter than the equipment they're working on.

If there is a change of state I will measure and record voltages on the old and new boards and post them. Maybe this will lessen someone else's time and research to get to a fix! In the meantime if anyone happens upon a spec sheet and can post it I'd sure thank you. I've done all I can to try and self-help.

And thank you everyone for your help, directions and suggestions!

[budm]

Re: Vizio E65x-C2 question about Gamma

https://www.badcaps.net/forum/showth...ighlight=gamma

[DXseekerMO]

Re: Vizio E65x-C2 question about Gamma

Thanks for the link budm. I thought I would go ahead and post the voltages from the VG_A and VG_B test points plus a few others, just in case someone might see something.

VG_A1…..11.21 VG_B1…..14.37
VG_A2…..11.06 VG_B2…..12.32
VG_A4…..11.00 VG_B3…..11.71
VG_A5…..10.98 VG_B5…..10.67
VG_A7…..10.96 VG_B6…..10.49
VG_A8…..10.94 VG_B8…..10.07
VG_A9…..7.76 VG_B9…..8.35
VG_A10…7.70 VG_B10…7.18
VG_A11…4.39 VG_B11…5.44
VG_A12…4.37 VG_B13…5.00
VG_A14…4.34 VG_B14…4.34
VG_A15…4.32 VG_B16…3.55
VG_A17…4.23 VG_B17…4.24
VG_A18…4.03 VG_B18…0.41

AVDD_L……...15.58
STATIC_HI…..15.32
VCOM…………0
AVDD_R………15.59

When I look at the pattern here it appears VG_B1 VG_B2 and VG_B18 do not follow. The others are fairly close to one another. The only other question is VCOM at zero volts, I verified it three times.

[budm]

Re: Vizio E65x-C2 question about Gamma

Those Voltages look to be really close to each other, I.E. A2-A4, A5 ~ A8, etc.
VCOM…………0V: That is not right. If you at some of the Voltages as reported in that link, Vcom should not be 0V.
Are you able to find VGL (Minus Voltage supply)?

[DXseekerMO]

Re: Vizio E65x-C2 question about Gamma

I'll look for it and see. What do you mean (minus power supply)?

[budm]

Re: Vizio E65x-C2 question about Gamma

If you look at that link, you will see the Vcom reported as - 5 ~ 6V because it is negative power supply which provide Negative Voltage.

[DXseekerMO]

Re: Vizio E65x-C2 question about Gamma

Verified no volts at VCOM again. VGL tested at -6.97v. Sounds in range with what you said.

EDIT: I tried downloading the spreadsheet but it doesn't seem to play well with my version of Excel.

[DXseekerMO]

Re: Vizio E65x-C2 question about Gamma

And if I'm properly reading this info I just found, missing VCOM voltage should equal no picture displayed on the screen? I also read that VCOM is related to contrast and this voltage is part of the gamma correction circuit?

This makes me wonder if something on the display is loading the t-con and mis-directing the VCOM voltage?

[DXseekerMO]

Re: Vizio E65x-C2 question about Gamma

I just put that theory to the test, unhooked both FFC cables from the t-con to the panel and VCOM is still absent. While I was at it I re-installed one FFC, turned it on and that side was gamma'd out.

[DXseekerMO]

SIGNIFICANT find!

The area outlined in the picture below is a bank of SMD caps right off the VCOM test point. When continuity testing across all of these caps they indicate short, .006 ohms. Furthermore there is identical continuity from the VCOM test point to chassis ground.

Other SMD caps in the area do not test short.

So I'm guessing one or more of those SMD caps in that bank are shorted and re-directing VCOM to chassis ground?

Does this sound reasonable?

[Andrew F. Ali]

Re: Vizio E65x-C2 question about Gamma

Vcom at 0V is your problem. No Vcom = low level contrast. If you can get a replacement T-CON Bd that is working your problem will be solved.

[akim uddin]

Re: Vizio E65x-C2 question about Gamma

samsung RV408 laptop power on but no display. there are all voltages ok but cmos battery (-12/18v) showed instead on +3v. how to solve this problem.

[Andrew F. Ali]

Re: Vizio E65x-C2 question about Gamma

samsung RV408 laptop power on but no display. there are all voltages ok but cmos battery (-12/18v) showed instead on +3v. how to solve this problem.

Hi akim uddin. Thanks for your query. However, some may take dim view on another person 'hijacking' another persons thread. Please start a new thread with your query to get help as you requested.

[budm]

Re: SIGNIFICANT find!

The area outlined in the picture below is a bank of SMD caps right off the VCOM test point. When continuity testing across all of these caps they indicate short, .006 ohms. Furthermore there is identical continuity from the VCOM test point to chassis ground.

Other SMD caps in the area do not test short.

So I'm guessing one or more of those SMD caps in that bank are shorted and re-directing VCOM to chassis ground?

Does this sound reasonable?

Yes, it can be one or more of those MLCC which are connected in parallel has shorted out, you can remove them one at a time to see if the shorts will go away, nothing to lose at this point.

[DXseekerMO]

Re: Vizio E65x-C2 question about Gamma

So this afternoon I removed the T-CON board to have a closer look at the caps in that bank. The visual inspection showed nothing obvious, no burn marks or arcing, they look normal, so like the good auto tech I was trained to be I "checked to make sure the problem still exists before continuing" and did an ohms check on VCOM with it out of the TV...and the short is gone.

My half-second of glee was immediately replaced by "oh s***, so now what else is shorted...and where". I re-installed the T-CON but with nothing hooked up, no short. I hooked up the cable from the main board, re-test, no short, but when I hook the FFC cables up from the source driver boards, either side, VCOM tests short.

Looks like I've isolated the problem to the panel.

[budm]

Re: Vizio E65x-C2 question about Gamma

I thought that test (disconnecting the FFC cable) was done in post 31.

[DXseekerMO]

Re: Vizio E65x-C2 question about Gamma

It was, but with the TV on and I was checking to see if voltage was present. I didn't do an ohms check until later last night and that was done with the FFC's hooked up.

[budm]

Re: Vizio E65x-C2 question about Gamma

I see.