Coby TFTV4025 Turns On and Right Back Off - Changed PS...Mainboard HS Caps?

[ImmaFixit]

I am working on a Coby TFTV4025 that has standby light, then powers on and the screen shows the INPUT for half a second and then TV shuts down to standby light.

Voltages on PS appeared OK, but a few caps looked suspicious. Attempting to change the caps, a pad lifted so I ordered a replacement PS supposedly in working condition.

TV still has same issue.

Suspecting mainboard 002-lt23-7611-00r V1 may be the problem.

Inspection shows 4 caps in the corner of the board that are covered with brown glue like substance, which appears in every photo of this particular mainboard. Two of those caps have tops that appear different than the other 2, which I will show in a photo attachment.

Question is, these caps only have HS (or SH depending on orientation) so is there someone who knows what their value should be if I should remove them from the board and test uF with multimeter?

These mainboards are listed rather expensive so obviously if I could get by with changing a few caps, that'd be great, but of course if I don't know the value, then I'm stuck.

Thanks for any input.

[mmartell]

Re: Coby TFTV4025 Turns On and Right Back Off - Changed PS...Mainboard HS Caps?

Sounds more like inverter trouble but it wouldn't hurt to see if you can't clean the glue up.

[Andrew F. Ali]

Re: Coby TFTV4025 Turns On and Right Back Off - Changed PS...Mainboard HS Caps?

Yes..Inverter or backlight jacks/connectors could be faulty.

[ImmaFixit]

Re: Coby TFTV4025 Turns On and Right Back Off - Changed PS...Mainboard HS Caps?

Thank you both for your time and information.

I went ahead and ordered a backlight inverter, can't believe they are as cheap as they are for this particular model.

I will report back the progress after I get it installed.

[newtothis]

Re: Coby TFTV4025 Turns On and Right Back Off - Changed PS...Mainboard HS Caps?

Did you check to see what the backlight on signal from main was doing first? Does it drop out?

[Andrew F. Ali]

Re: Coby TFTV4025 Turns On and Right Back Off - Changed PS...Mainboard HS Caps?

Did you try self testing the Power Board??

[newtothis]

Re: Coby TFTV4025 Turns On and Right Back Off - Changed PS...Mainboard HS Caps?

First thing I would of done is remove that glue, It becomes conductive when it browns.

Next would be to check all voltages on PSU when set is On and when the set faults. This includes the BL-ON signal from the mainboard.

[ImmaFixit]

Re: Coby TFTV4025 Turns On and Right Back Off - Changed PS...Mainboard HS Caps?

The $6 inverter board came in today and did not resolve my problem, which I should have realized that the TV's blue light goes from standby, power on, then off with the inverter board not connected.

I will try removing the glue and seeing what happens.

It was a while ago when I tested the original power supply board, the readings from what I remember were ok (matched the values painted on the board). When I lifted a pad replacing a cap I thought may be bad and bought a replacement power supply, I did not test it because it appeared to look ok and the seller who I'm sure wouldn't fib said it was in working order, which lead me to figure bad main board that are over $70 if one can be found and quite a bit to spend to repair a Coby....but I'd bite the bullet on a couple of "HS" or "SH" caps if I knew what their value was supposed to be.

Thanks for everyone's replies and help, I'll check back in with progress after removing the glue.

[ImmaFixit]

Re: Coby TFTV4025 Turns On and Right Back Off - Changed PS...Mainboard HS Caps?

Here is a little bit better photo of the caps I question and the glue all over them and a few other places on the board, including a connector close by that is slightly out of the picture. It is going to be a chore...

[newtothis]

Re: Coby TFTV4025 Turns On and Right Back Off - Changed PS...Mainboard HS Caps?

Ok lets confirm voltages on the PSU first and also the signals from the mainboard.

[Alastair E]

Re: Coby TFTV4025 Turns On and Right Back Off - Changed PS...Mainboard HS Caps?

Those devices in the third picture.....

They Are NOT Caps!

They are Inductors--See on the board, Marked L summit or other not C summit or other, and positioned in that horrible way--probably for a reason!.....

A Little Knowledge--Is a Dangerous Thing.....

[newtothis]

Re: Coby TFTV4025 Turns On and Right Back Off - Changed PS...Mainboard HS Caps?

LOL I didn't even look at the pics yet as just wanted to say not to buy an inverter before proper diagnosis

[ImmaFixit]

Re: Coby TFTV4025 Turns On and Right Back Off - Changed PS...Mainboard HS Caps?

Ironically, it's the second time this week I've heard someone refer to the phrase "a little bit of knowledge is a dangerous thing" but they weren't using it in reference to me, lol...

Thank you for the advice. I apologize for ignorantly calling the HS inductors "caps" when a googley image search does eventually show a picture of the same HS inductors, which I've never dealt with before and didn't know what to call them. Not too sure if the way the wrapper appears to be loose at the top of one is a sign of being bad similarly like a cap could be, but I can look that up on my own if need be.

Thank you for the suggestion about the "glue" becoming conductive. After looking up "how to remove the brown glue on circuit boards", it appears to be a pretty common failure over time, but I haven't found much about removing it other than using a hobby knife and patience. The way it is covering directly over the top of connectors, etc. it would certainly cause a bridge.

I will make a handwritten paper graph with all the printed values on the PS then their value on standby and then their value for the 8 seconds the TV does power on.

Fingers crossed I get lucky that I can replace just a simple part on a board instead of it being a BGA or similar.

Thanks for everyone's patience, information and assistance.