Insignia 26" power board need help

[infringer]

I have a insignia power board which had a blown fuse upon initial test.

I replaced the fuse and it blew.

Upon inspection I determined that the bridge rectifier was faulty.

I replaced the bridge rectifier and the fuse.

I turned on TV and the red light blinks 5 times then goes to solid red.

So next I hit the power button and it stays a solid blue like it should but there is no picture.

So I popped it open and tested the voltage lines going to the backlight and found there is no 24v going to the backlight.

What would be possible causes to this issue.

Pics are attached for additional explanation and making your job easier to aid me if possible.

[budm]

Re: Insignia 26" power board need help

OK, Can you please take good closed up pictures of the 2 white connectors if they have any labels on the them to tell me which pin is PS_ON, BL_ON.
Also check the DC voltage on that large black cap in the primary side, it should have 165VDC when TV is plugged in, and around 400v when TV is turn on.

[infringer]

Re: Insignia 26" power board need help

budm the pics are already there and they are clearly labeled all you need to do is click on the 5th pic then when it comes up click on it again and you can see the full resolution picture and then zoom in on it the markings are very clear actually....

[budm]

Re: Insignia 26" power board need help

OK, my eyes are not that good, I had to really zoom in to read them. So what DC voltage do you have at PS_ON and the ON_OFF pins, and also the DC voltage on that large cap?

[infringer]

Re: Insignia 26" power board need help

Cap in standby red light= 166.5v
Cap when on blue light= 393.6v

[infringer]

Re: Insignia 26" power board need help

When blue light is on and powered on here are the voltages:
ON/OFF= 3.285v
PSON= 2.734v

Note these are measurements from the video board connector on the power supply.

[infringer]

Re: Insignia 26" power board need help

Here are some more pictures to help determine whatever is wrong I don't want to guess here unless it is educated but I have 2 nagging suspicions on what the problem is but I will resort from guesswork unless there is something educated pointing me in such a direction.

Anyhow here is the pics...

[infringer]

Re: Insignia 26" power board need help

Ok the picture is working but the backlight is not turning on after the flashlight test is this because of the power board or is it because of a circut that is still the question.... Got to dig deeper on this the on off and power on seems to be working...

[tom66]

Re: Insignia 26" power board need help

If you don't have 24V that's where I'd look as you have no backlight.

Since you have a picture the main board is probably telling the power supply to switch on.

But it's worth checking it anyway...

Is there a pin marked PS-ON on your power supply?

[infringer]

Re: Insignia 26" power board need help

Here are measurements taken from the power board connections:

PSON = 2.734v when on
ON/OFF (out to video board) = 3.2v when on
ON/OFF (out to backlight inverter board) = 3.2v when on
All 24v (out to backlight inverter board) = .100v when on

Big Filter Capacitor (When in standby) = 166.5v
Big Filter Capacitor (When on) = 393.6v

PS I attached better closeups of the power connectors...

Thanks guys hope this helps.

[tom66]

Re: Insignia 26" power board need help

Is PSON much lower when TV is in standby?
It looks like the main board is working fine, so the problem is on the PSU.

[infringer]

Re: Insignia 26" power board need help

PSON (standby) = .098v

Either that or the backlight itself could be bad but you would think the 24v out would be higher unless there is something that reports the backlight as faulty errr IDK keep trucking dunno what to check next been checking resistors and such in the mean time still going at it but an educated approach would be better...

[tom66]

Re: Insignia 26" power board need help

OK, do the 5V and/or 12V change when in standby?

I think the 24V should measure more than 0.1V! I think that if it is low, it is likely a PSU problem, but it is possible (though unlikely) that the backlight inverter is shorted out. Normally it would blow the fuse on the inverter though, which would allow the 24V to come up.

[infringer]

Re: Insignia 26" power board need help

well according to what I am reading there is no 12v on the video board connection it reads
0v when in standby and then .003 when powered on....

+5v(video board connector) is at 5.00v when on and remains the same whether standby or on
+12v(video board connector) is at .003v when on but is 0v on standby
+24v(video board connector) is at .100v when on but is 0v on standby

I will try to reply if not I will be back tonight I do have a family gathering to attend. But please do respond as I may be able to do a bit more before I leave.

Thanks

-infringer-

[tom66]

Re: Insignia 26" power board need help

Hmm, do you have any sound from the TV?

12V should power the sound amplifier and is run from the same supply as 24V.

Very odd the TV would work without 12V, but I guess it generates everything it needs for a picture (without backlight) from 5V.

[infringer]

Re: Insignia 26" power board need help

Good question I will have to test this I find it odd as well you'd think 12v would be a requirement the picture that I refer to was just pressing of the menu button no video source has been plugged in at all during the testing or repairing of this TV I figured seeing the menu would be the best indicator.

[tom66]

Re: Insignia 26" power board need help

It points to a problem with that main supply. Likely a shorted diode or a bad startup capacitor. Since 12V is dead zero, I'm thinking the fault is there.

Can you post a picture of the underside of your PSU?

[infringer]

Re: Insignia 26" power board need help

Already posted:
https://www.badcaps.net/forum/attach...4&d=1350181740

check that out already posted there is an 8pin IC903 on the bottom if you look IDK what it is possibly a voltage reg ic or something the plastic is busted off the top but nothing looks melted or fried so I didn't really concern myself with it just left it on the back burner and will continue to ....

I await expert advice instead I would rather learn the full process of testing and diagnosis then waste my time being a parts swapper.

[budm]

Re: Insignia 26" power board need help

OK, I look at the board layout, this power supply has always on 12V power supply , its output is stepped down to 5V for the logic circuits. So you should always have 12V and 5V at the output connector at all time.
The switched 24V is just a single output for the backlights inverter board.
The power supply also has PFC Voltage booster circuits.
The bad news is that the SMPS IC that blown its top is for the 24V power supply, and it is very likely that the MOSFET for the 24V has Gate to Drain shorted out so it dumped 400V into the SMPS IC.
This TV also use CHIMEI backlights inverter that is famous for bad transformer and blown fuse for the PWM IC.
So verify that you do have 12v, it must have 12V otherwise you will not have the 5V because the 5V is generated from the 12V section.
The bad part is to figure out the P/N of that blown IC, and you will need the MOSFET and component around the Gate drive circuits also, lots of work!

[infringer]

Re: Insignia 26" power board need help

hrmmm oddly contrary to what you say I have 5v but I do not have 12v and the picture on the LCD I can see with a flashlight no video or sound but I can see the OSD menu ...

Very tuff I know but this is what I have found so far my +5v's are all fine metered at 5.00v when powered on 12v I have almost nothing and 24v I have almost nothing... Che Mei or however you spell I have seen lots of backlight issues with these screens as well in computer displays specifically and normally it has been corrosion and the backlight harness arcing off on the frame almost as if they didn't truely use the proper hi temp wire and cut corners in this manner. It is interesting to know that the power board issues would arise from their backlights I would think that would all be on the power board and inverter board engineers more so from the engineers assembling the rest of the TV or monitor with their power circuits.

Anyways with all of this I don't wanna get too much more off the subject but is there anything that you would suggest to test next in circuit which mosfets or voltage regs would you suggest I check ....

Yes this is a wild one but I do have 5v's weather standby or powered on...

PFC = Power Factor Correction for those reading used in many newer SMPS = Switch Mode Power Supplies to keep things in respect to all those learning ATX computer power supplies use this to as they too are switch mode power supplies.

Thanks for taking all that time to try and understand and label the cirucuits for me I must keep searching though I will go on a hunch that you are right about the 12v rectifier and give that a look tomorrow after a hard day of work.

Thanks a bunch budm and tom66