Sceptre X505BV, blue LED, no display

[tom_h]

Hello all,

I have a Sceptre X505BV-FMDR8HJ1PE8 tv that had been gradually over time taking longer
and longer to come on, now it will no longer display any image. Original symptoms
are the red standby LED would turn to blue immediately when pressing the power on
button, but there would be a delay for the "SCEPTRE" image to appear on the screen
and backlight to come on. The delay kept getting longer, then it would go from blue
LED back to red. Then when I pressed the power on button again it would bring the
display up and work fine. The delay kept getting longer and longer, now the image
and backlight will not come up at all, just the blue LED remains on. I cannot see
an image with a flashlight either. The gradual delay made me think I was having a
capacitor going bad, but inspection of the power supply board shows no bulging caps
or hot spots on either side. Voltage readings below seem normal except for the 12V
which varies between 13.48 and 13.53, which after it is on a while, will eventually
drop down a little and toggle between 13.28 and 13.32 (highly suspicious I suppose).
This tv has the AY160D-4HF06-080 power supply board. Can anyone give me any clues
on which component on the board controls the 12v line or what to try next? I am
going to try to post a picture of the board. I've got old eyes, so trying to follow
traces on the board is a bit of a challenge. :-)

5V = 5.12v
24V = 24.7v
5VSB = 5.12v
PS/ON = 4.53v
BL/ON = 59mv
ADJ = 5.05v
12v = 13.50v
backlight plug = -.691v

Thanks

Tom H.

[EazyBone]

Re: Sceptre X505BV, blue LED, no display

Bulging caps isn't the only indication a capacitor is bad. You have to test them. Voltage should no be dropping like that and I would suspect the power board in this.

The real way to test the caps would be to remove them from board and test them (I think, sort of new here) or use a dscr meter.

What do the main caps read when the TV is on? Does the voltage drop or stay same?

But 12v lines shouldn't be 13.5 either that's too high.

Are you trying to fix this on a component level or just replace the board

[tom_h]

Re: Sceptre X505BV, blue LED, no display

Thanks for the response. I am trying to figure out if I can bring that 12v line to the correct level if I can determine which caps/regulators are involved. ShopJimmy does have the power board but not the mainboard available. I'm concerned that the mainboard may have been compromised due to the fact that I see no image with a flashlight, so I didn't want to buy just the power board and have that not help. Plus, I don't have a backlight tester and am unsure if I can jumper it safely in some manner to get power to the BL plug/jack to see if there are any issues with the LED's in the backlight on top of the 12v power issue. I realize that often caps don't bulge when failing, that's why I was wondering if there were specific caps to replace since this seems to be a common power board in these flatscreens.

[nomoresonys]

Re: Sceptre X505BV, blue LED, no display

Heat the electroltic caps on the powerboard with a hairdryer for a couple minutes, then try the tv, don't wait til it cools off to try it, see if there's any change if only for a bit.

[tom_h]

Re: Sceptre X505BV, blue LED, no display

Yes, I was thinking of trying to heat up the 5 larger electrolytic caps nearest the connectors a few days ago. Wasn't sure if I might wreck something else doing that, though. I'm going to try to get a magnifying glass from a neighbor to see if I can find which one might go to the 12v regulator (if I can find which one that might be) following the land traces over the weekend. Other thought was trying to channel the heat just to those caps using a couple pieces of cardboard to sort of protect anything on either side. We had a portable cap meter at work many years ago that I could have borrowed if I unsoldered the suspect caps, just not sure where it is at this point in time. I'm welcome to any/all suggestions at this point. One thing I did notice is that all the voltages remain solid, EXCEPT for the 12v testpoints which still vary slightly, yet consistently per my opening post.

[nomoresonys]

Re: Sceptre X505BV, blue LED, no display

The good thing about using a hairdryer for this test is if your only heating for a couple minutes, it won't ruin or melt anything on the board, it's just a simple test that may find a marginal/faulty cap.

[tom_h]

Re: Sceptre X505BV, blue LED, no display

I tried heating up the caps on the cold side of the board. The only voltage that changed was the 24.7v went up to 25.2v, then once the board cooled down it went back to 24.7v. The 5v remained at 5.13 and the 12v remained at 13.5v.

After this, I unplugged the cables from the mainboard to take it out of the picture, jumpered the PS/ON to the 5VSB with a 1k resistor and measured again:

24v = 22v

12v = 12.2v

5v = still holding at 5.13v

After that I also added another jumper with another 1k resistor from the 5vsb to the BL/ON and measured again:

24v = 23.85v

12v = 11.97v

5v = 5.13v

Also, the backlight came on after a 2 second delay at 233v. I checked the front of the panel and there appears to be no dark spots, so I believe the backlight has no problems. So, the 24v came up a little when I also jumpered on the backlight, yet the 12v went down a little bit. 5v still holding at 5.13v no matter what is jumpered or if the mainboard is in-circuit. I'm not sure at this point why these voltages would go up with the mainboard/cables attached to the powerboard. Seems strange to me. The 24 volt cable connects to a 4pin plug labeled as "Amplifier" on the mainboard, so I'm wondering if the 24v is only used for powering the audio section - leaving it disconnected from the mainboard with the other cables plugged in had no affect on the voltages. I don't know if the voltages are higher with the mainboard is in-circuit due to a higher current draw or if I still have a potential capacitor issue. Either way the mainboard is not telling the backlight to turn on and I see no image using a flashlight - not sure if it is safe to jumper the backlight to "on" with the 1k resistor to confirm there is definitely no image with everything connected. It remains with the symptom of the power switch will change the standby LED indicator from red to blue, bring up the voltages, but will not turn on the backlight or show an image from what I can see using a flashlight.

[nomoresonys]

Re: Sceptre X505BV, blue LED, no display

Wen you are trying the flashlight test hit the menu button, check for text on the screen. What I meant by try the tv after you heat the caps is plug it in and hit power, see if you get a display briefly.

[tom_h]

Re: Sceptre X505BV, blue LED, no display

Considering that I was able to confirm that the backlight was good and the fact that the TV worked fine with a good picture as it took longer and longer to come on, my best guess was that the T-con strip along the bottom of the panel was good and that the problem seemed to be isolated to the mainboard. With the mainboard connected, I continued to get the 13.5v on the 12v rail that would drop down to 13.3v after about 40 minutes. I was able to probe a few testpoints on the mainboard showing 3.3v and 1.8v on some of the labeled pads on the bottom of the board. But I then found a mainboard available on Ebay from a place in Miami Florida, so I ordered that for $30. After installation, the picture and Sceptre logo came right up on the screen after about 5 seconds, similar to how the TV booted up as new. The 12v rail then showed 12.43v and remained the same for a few hours (at least that seemed closer to what I would expect), so I reassembled and hung it back on the wall. It's been running at least a few hours a day for the past 10 days and seems fine. Sure would be nice to have schematics to poke around on the original board to find out where the issue was. I may resume checking the chip caps and look for shorts elsewhere at some point on the old board when we get stuck inside for the winter. Hoping this helps someone else that may have a similar issue in the future on this model. Thanks for the responses in the string above. :-)