Sceptre X32

[thetonywarren]

Sceptre X322BVHD8WXESBV2. Mother in law said her tv wasnt working again, I fixed it a couple of months back, it was shorting from carbon build up due to overheating on a part of the board, this is apparently a known issue and has occurred on numerous similar sets. I cut the board where the carbon had built up and coated all parts with rtv high temp silicone and it was fixed.

This is a different issue now. She said the tv picture was black in the middle but you could see it around the edges, I confirmed this, and brought it home to take a look. I turned it on and this time there was no backlight on at all, but I could see the menu on the screen, so the video signal is getting there.

I have replaced some of the caps now, and tried it again, but same issue, no backlight. Is anyone familiar with this power supply board that can walk me through troubleshooting the board?

I have replaced the 8 blue caps in the lower right hand corner of the board. If anyone can offer any assistance, it would be greatly appreciated.

Thanks.

[Agent24]

Re: Sceptre X32

Some things don't seem to add up. How could you see the menu if there was no backlight? Or were you shining a light on the LCD?

If you can see *anything* on the screen normally then the backlight is OK. If you are only getting the menu but no TV stations, then it may be a tuner\image processing problem instead.

[thetonywarren]

Re: Sceptre X32

I could see the menu in the corner of the screen by shining a light on the screen. The backlight was NOT on.

[thetonywarren]

Re: Sceptre X32

Anyone have any systematic troubleshooting guide? I have gone through budm's guide and read over other guides, but it really isnt a comprehensive guide that walks me through checking each component and/or circuit. I do realize these TV sets are all unique and each is set up differently, but I would think there are ways to step by step go through the board from 120VAC into the board all the way to output to the lamps/led's and video signals. Any help would be great. Please let me know if anyone has any assistance they can lend. I am good with a soldering iron and multi meter, and I also have an esr meter and a Peak Atlas DCA55.

Help Please!!!

[Agent24]

Re: Sceptre X32

I'm not an expert with these either, but I'll say what I can. First would be to narrow down the problem location.

Checking voltages would probably be a good start, to check that the PSU is functioning OK. Under the blue capacitors there are some multi-pin connectors, they appear to be labelled with voltages. Check that these are present and correct. Make sure you measure them with respect to 'cold' ground. The rails that come out there likely also power the inverter. You can verify this by looking at the PCB traces.

What is interesting was how you say the picture was only visible around the edges - that could indicate low output voltage causing the CCFLs to only light at the ends, and hence only light up the edges of the screen.

Budm has a guide here https://www.badcaps.net/forum/showthread.php?t=19987 to test the inverter with other lamps, then you could find out if it's the lamps or the inverter. (Although I don't know if that is only suitable for monitors, or if it would work for TVs as well)

Here's a thread about the same model TV: https://www.badcaps.net/forum/showthread.php?t=34223 it might be useful.

[budm]

Re: Sceptre X32

OK, the DC voltage right at the two legs of the main filter cap, do you get about 360~400Vdc when TV is turn on? The inverter circuit of this power supply needs that much voltage to run. I remember seeing this power supply board on the thread some where.
Is the power supply MEGMEET MP329FL?

[thetonywarren]

Re: Sceptre X32

Here's what I have checked/changed currently. Im not sure which is the main filter cap, I have noted on the board, what I think is the main filter cap, and I tested with my dmm set to vdc, and I get from 510-550vdc when i have my leads across the positive and negative lead of the large cap on the board. If that's not correct or if you have other suggestions, please let me know.

BTW, it is a Megmeet MIP320FL-T3

Thanks!!

[tom66]

Re: Sceptre X32

Is the battery in your meter OK? For reference can you check a fresh AA battery - should read 1.5~1.6V.

[thetonywarren]

Re: Sceptre X32

I'll check my DMM and make sure the battery is ok, then I'll test a AA and post the results, btw, am I testing the right area? Is what I have noted the main filter cap? And am I testing it properly with my dmm set on vdc and just check across the cap on the pos. and neg. legs?

Thanks!!!

[Agent24]

Re: Sceptre X32

Yes that is the main filter cap, it's always the big, high-voltage one near to where the AC cord comes in, although in some designs (usually older ones without active PFC) they can have two.

[budm]

Re: Sceptre X32

That is correct, measure the DC Voltage right at the two legs of the main filter cap, that cap is rated only at 450VDC and there is no circuit in that section to produce 550VDC, that cap would have blown up by now with 100V over the rating, so the meter cannot not be working right.
This power supply board does have PFC Voltage booster.

[thetonywarren]

Re: Sceptre X32

Ok, so my meters 9v battery was low, changed it out now I have a better reading. I am getting 390.6vdc at the main filter cap. What does that tell us?

Thanks guys!!

[Agent24]

Re: Sceptre X32

That should mean that the primary input components and the PFC circuit is OK.

[budm]

Re: Sceptre X32

OK, so the PS_ON signal is good because it does turn on the PFC circuit, next we need to find out if you are getting the BL_ON signal or not from the main board. We need to locate that pin on the board. It looks like BK pin is the BL_ON pin, see what DC voltage you have on that pin.

[thetonywarren]

Re: Sceptre X32

Are you saying that I should check VDC on the BK pin and ground. Is the BK pin on the power supply board or the other board that has the video signal. Sorry I dont know all the technical terms for these boards. Im assuming the BK pin is one of the ribbon wire points on one of the boards, correct?

Thanks!!

[budm]

Re: Sceptre X32

It is on the power supply board connector, BK and the chassis, DCV.

[thetonywarren]

Re: Sceptre X32

BK pin to chassis ground show 3.125vdc when set is turned on.

Next?

Thanks again guys!!!!

[budm]

Re: Sceptre X32

That is good. I will need to trace the connection for the voltage from the power supply to those two MOSFETs that drive the inverter transformer, I expect some kind of fusible resistor feeding that circuit.

[thetonywarren]

Re: Sceptre X32

Thanks budm, let me know what you find.

[thetonywarren]

Re: Sceptre X32

Any ideas? Find anything? Let me know if you can.