Rca rlded5078a-d no backlight

[microvibe]

I have no backlight but sound is there and I can see picture with flash light. I do have 3.02v at blon have 12v no 5v on the pinouts but I have standby light and it's turn blue stays on when power pressed. Across big cap I have 385v. When first powered the transformers seem to whine squeal. No voltage or voltage spike at backlight connector.

[budm]

Re: Rca rlded5078a-d no backlight

Put the black probe on the chassis, Red probe on the LED connector with red wire then turn on the TV and see how high the Voltage jumps up to and wait a few seconds to see how low it drops down to, then do the same on the LED connector with the black wire, then do the same thing over with the LED connector removed from the board.

[microvibe]

Re: Rca rlded5078a-d no backlight

I get up to 3volt. At connector with it disconnected no volts when connected.
On left side of transformer closest to large cap when press power takes few seconds but here little weird whine buzz then volt spikke to 200v on right side transformer will spike to 30 Ish volts.
I tested cap in continuity mode it's. .573 have same cap in another board same setting and it's 0l open

[dick_barton]

Re: Rca rlded5078a-d no backlight

What voltage do you have on this connector at each pin when you switch on. For your information there are 5 strips of 14 leds according to an earlier post.

[microvibe]

Re: Rca rlded5078a-d no backlight

I don't have that power supply. Mine is ay128c-1mf27-080 posted a pik of it previous post

[dick_barton]

Re: Rca rlded5078a-d no backlight

OK Thanks. Then what voltage do you have on the pins on Con4F when you switch on.

[microvibe]

Re: Rca rlded5078a-d no backlight

When switch on quick spike to 3v that's it on con4f

[CapLeaker]

Re: Rca rlded5078a-d no backlight

Umm... that's not good. Check those 4 diodes below that connector.

[microvibe]

Re: Rca rlded5078a-d no backlight

The diodes test good. How about that Grey cap by main cap. I get spike to about 200v to left side of transformet

[CapLeaker]

Re: Rca rlded5078a-d no backlight

Can we see the back side of the board too?

[microvibe]

Re: Rca rlded5078a-d no backlight

Here bottom

[budm]

Re: Rca rlded5078a-d no backlight

It look like there are lots of bad solder joint on that connectors that joins the two board together.
https://www.badcaps.net/forum/attach...7&d=1485999890

[budm]

Re: Rca rlded5078a-d no backlight

BTW, that grey cap by the main filter cap is the dc blocker/coupling cap for that LED power supply transformer which driven by the two power MOSFETs next to it.
Look real close at the cap to see if the sides are bulging out or not, also check the capacitance.

[microvibe]

Re: Rca rlded5078a-d no backlight

I cleaned up bad solder joints and swaped out cap for one from working board same specs. Still no difference

[CapLeaker]

Re: Rca rlded5078a-d no backlight

So everything is fine with the working board?

[microvibe]

Re: Rca rlded5078a-d no backlight

No TV still does same I only took a good capacitor from working board not same kind of board but same capacitor

[CapLeaker]

Re: Rca rlded5078a-d no backlight

Ahh... you said something about a squeal from a transformer. Can you pinpoint to which one? Take something like a wooden spoon or something else non conductive. Also you said no 5V. I can't see any 5V supply.
Measure the DC voltage on each of the Pin that goes between the PSU and the main board and please use the proper pin out name too.

[Mayn]

Re: Rca rlded5078a-d no backlight

I just fixed the same tv with the same symptoms. Was a bad led. luckily I had spares.

[microvibe]

Re: Rca rlded5078a-d no backlight

Reviving my old thread. Pulled apart tv again . Replaced one bad led rest test good. Before replacing the bad LED I swap parts on the power supply now when I switch on I see the RCA logo but back lights are very dim and I'm only getting 165 volts across the large cap. Where do I test to see what's failed that's not giving 365 volts

[microvibe]

Re: Rca rlded5078a-d no backlight

What area of power supply is the 360volt for leds created trying to find why only 165v across they large caps.