0.5ma would not be enough to light the LEDs. I would think (guess really) that 5-10ma are about the minimum for lighting the LEDs enough to see a picture, even a dark one. Are you on DCA on your meter? Can you see the backlights lit from behind the TV? There are usually small openings where you can see the backlight leak through from behind with the rear cover off the TV.
Is there a schematic for this TV on line?
John...
JohnCT
Lurker
Last Activity: 04-09-2024, 10:59 AM
Joined: 04-10-2018
Location: Hartford CT
-
I bought an LC75 brand new in the early 80s, then added a 102 later as I opened another location. When I started contracting, I got rid of the 102. Sometimes too much automation is not our friend - the 75 is much faster. It's like trying to change the temperature on my wife's car - I have to scroll through menus where on my older truck I reach over for the temp knob without even looking at it.
John -
Before you do anything, unsnap those two ribbon cables and take a look at them closely to make sure there's no arcing or even melting of the ribbons.
That's good news. I've actually seen some TVs come in where sections of the LED strips start failing one by one and the customer doesn't bring them in until it's unwatchable - kind of throws the diagnosis off. Between its age (under a year) and your description, it's unlikely you have to go inside the screen unless there's something really strange going on - like a burned strip that might be grounding itself to the frame....Leave a comment:
-
Your TV uses a common voltage source (VLED) for all four channels of your back lighting circuit, and four individual "sink" type drivers for each of the two sections of the two LED strips in the display screen. Even if that voltage checks normal, it won't tell you if the LEDs are actually being driven hard enough to produce a normal picture.
The regulation of the supply to the LED strips is not based on voltage but current. If you can open one of the cathode lines and check the current we can get a better idea of what's going on. The common VLED voltage could be fine...Leave a comment:
-
Well, to be honest, I never replace the 4.7z because it protects Source pin of the internal mosfet which is almost at ground potential. The way I see it is the only way that pin goes anywhere near zener voltage is if the chip is blown up anyway.
I had considered the possibility the other four missing zeners might serve a similar function as the 4.7 z but then dismissed it figuring one of them at least must be for a reference. Since I have a bunch of those LD7913s in stock and I'm retiring in June anyway, what the heck? Nothing to lose.
So I installed a LD7913 and put...Leave a comment:
-
Parts ID for Vizio power board model E550i-B2 DPS-167DP-1
The short story is that I have to repair board this for someone and it has the typical standby IC failure (LD7913, Schottkey, and Z909 4.7V zener), but someone has harvested some other zeners from the same circuit <sigh> before I got it. Everything else is there.
I know this is a long shot, but has anyone ever documented the zener values in locations Z900, 902, 904, and 907? I assume there's no schematic of this board?
Thanks.
John -
Re: Need firmware for Sony KDL-48W600B
Thanks sir.
The file is only about 250M, most Sony bins are like 1.5G??
John...Last edited by JohnCT; 01-14-2023, 08:39 AM.Leave a comment:
-
Need firmware for Sony KDL-48W600B
Sony apparently deleted this from their support page.. Thanks.
John -
Re: Samsung UN50MU6300 burnt tab bond
If it's the screwless type, you have to insert a Samsung sourced tool (I use a screwdriver) at the bottom left and bottom right access holes.
Lift the tool upward until the bottom corner pops, then slide the tool **upwards** and across the top prying upwards as you progress. Do the same for the other side.
DO NOT slide the tool along the bottom edge or you will destroy one or more ribbons from the address boards to the display.
John...Leave a comment:
-
Re: Panasonic SC Board - BAD 30F131 IGBTs
I have one of those (can't resist a toy).
That tester will tell you if what you bought is a igbt, mosfet, transistor, polarity of same etc., but it will NOT tell you if the parts are counterfeits or lower amp/volt/watt devices in the same series reprinted to reflect the higher spec'd device.
I have run into crappy parts going back to the early 80s that worked for a while and crapped. Some were pure counterfeits, others reprinted.
A curve tracer might be able to tell you more but...Leave a comment:
-
Re: Samsung UN48J5000: Backlight Strip Burn
No, not in the context of shorting LEDs in a string powered by a current regulated source.
For argument's sake, let's assume the back light is set to a predetermined level and fixed (that is, not active to scene content) so as not to throw any variables into the discussion.
The TV monitors the current and adjusts accordingly. As LEDs short out in the string over time, the voltage *across* the string will necessarily drop to compensate for the shorted LED in order to keep the...Leave a comment:
-
Re: New TVs LED issues
When new TVs come out of the box, they are defaulted (generally) to 100% backlight level. If you take two TVs, set one up to "retina scorch" and the other to replicate an accurate studio monitor, 100% of the people walking by will say the retina scorch model has a better picture than the accurate one. This is the same as doing an A/B listening test with stereos; set one with bass and treble cranked and people will pick that every time.
BUT, it gets worse because some models have a "HOME" or "DEMO"...Leave a comment:
-
Re: Samsung UN60FH6003 yellow tint 3 days after replacing backlights
Thanks. If they say it, I believe it. I'm just not convinced that all of their LED strip offerings are "made for them", but I am that your version is new stock.
Can you post a picture of what you're experiencing? From your description it might be a erratic LVDS harness or associated connectors between the main and tcon.
John...Leave a comment:
-
Re: Samsung UN60FH6003 yellow tint 3 days after replacing backlights
Yes, because I was relaying the story of the Vizio model known to be a main board killer and three replacements were all bad. The point was that you can buy replacement parts and still be bad, and that I don't think (pure opinion) that SJ tests parts. Exception to that is the LED strips, which are quite easily and quickly tested. They will however replace any part immediately and with no trouble. Still, if an LED strip had few hours left before the screen was damaged or the TV suffered some other...Leave a comment:
-
Re: Samsung Plasma PN50C450 Click, clickity, click, click, click
Possible yes. Likely? Not sure.
You can check the buffers for leakage by using a dmm. I'm sure there are threads that show how to check from the input connector to the ribbons. Most buffer damage can be picked up that way.
Are you sure about your Y sustain replacement? The vast majority of this Samsung series failure is because of sustain damage, often caused by a shorted buffer. If the donor TV had a bad sustain (not unlikely), then your replacement could also be bad....Leave a comment:
-
Re: Samsung UN60FH6003 yellow tint 3 days after replacing backlights
We've had lots of defective parts from SJ. While some of their parts could be from new stock damaged in shipping, it's my opinion that most of their parts are those culled from TVs being recycled, either from a broken screen incident or electrical failure.
One shop I know bought three Vizio mains for a certain repair job from SJ and they were all bad, mostly because certain Vizio mains are good for maybe 2000 hours before they die and is the primary reason they are scrapped...Leave a comment:
-
Re: Samsung UN48J5000: Backlight Strip Burn
I've only seen one LED drive circuit that used a fix voltage for driving the LED string (small, low end no name TV). In that one example, a single shorted LED would indeed increase the current to the remaining as the voltage was regulated.
However, in these Samsungs it's the current that's tightly regulated. As individual LEDs short, the current is maintained but the voltage *across the string* will change to maintain string current while the voltage drop across each individual LED remains the same.
...Leave a comment:
-
Re: Emerson LC401EM3F No power - Please Help
Transformer failure these days is extraordinarily rare.
The first thing to check is the pfc voltage across the big electro. If the failed board is reading more than a couple of volts lower than the good board, investigate the pfc circuit (or even the cap itself).
Did you try heating the board?
John...Leave a comment:
-
Re: Fake Semiconductor headache
Fakes most certainly exist.
Back in the 80s were wondered why audio amplifiers would blow up days after being repaired and properly biased. I can't tell you how many LA series deflection ICs, STK power regulators, Motorola and Toshiba audio outputs, Hitachi horiz outputs etc failed soon after installation. Once we figured out it wasn't us or the customer abusing our repaired items, we knew it was the parts.
You can find many post-mortem photos of semiconductors that are phonies on the web. Back in the...Leave a comment:
-
Re: 150uf at 450 wv Large Capacitor Blown - I've Never Seen This... Have you?
Not sure of your question.
If the pfc filter is vented and dried out, just change it. Change any other electrolytic caps on the primary side that check high ESR or show signs of venting (values between 2.2 to 47 ~ 50v for instance). Otherwise, just change the pfc cap and go.
John...Leave a comment:
No activity results to display
Leave a comment: