Grundig 32VLE5303 - 3 dead LEDs

A friend brought me his mom's TV. It did not show any picture, but sound was ok. The first test in "no picture" situations is to take a flashlight and shine it on the screen. The image was there, so it had to be a backlight problem.

The 25V for the inverter checked ok and stable. After dismantling the panel I pulled out my LED backlight tester. And this was the result, three LEDs on the top were dead. Most likely the heat is accumulating at the top and those die first.

In this model, the inverter is mounted inside the panel.

I asked for help in the IWENZO Forum and a member sent me 10 LEDs. Thank's Jens! In the meantime I ordered a sack full of LEDs from Aliexpress.

I used a spatula to remove the strips from the panel. They were glued with adhesive tape, whose glue was hardened already.

To test a single strip, use the test points at the socket end. The polarity is printed next to them.

The plastic lenses had to be removed forcefully. They had been melted onto three black plastic pins.

The first surprise was that the replacement LED had cathode and anode swapped. The large pad was the anode. So the large pad on the LED had to fit on the small pad on the strip, which moved the LED out of the original center.

This is way too much solder paste, by the way. I shorted the LED out with that. Half of the amount is just right.

I soldered the LEDs with 370°C hot air.  This turned out to be a good compromise between speed and melting the LED lens. Using the iron was impossible due to the pad swapping. The small pad on the strip just was not reachable anymore. You will see the LED start floating once the solder is melted. It is a pretty easy and clean job.

Testing the new LED:

Testing the backlight again:

At the first attempt, I did not take much care about the lenses. I centered them on the LEDs and glued them with plastic glue. The result was this:

Ugly clouding! Why was that? The lenses have to sit perfectly perpendicular on the strip. Once they are skewed a little, their light beam doesn't hit the diffuser plate in a 90° angle anymore.

So I removed the lenses once again and used a file to make the pins on which they rest perfectly flat. The black pins on the strip got the same treatment. They were uneven due to the hot air and forceful removal of the lens.

Now this looked much better:

The clouds are almost gone. You could still see the new LEDs, which are brighter and more blueish, but that wouldn't be noticeable with normal images.

Her cuteness Juno Temple was happy to test the new backlight.

The backlight intensity was set to 100. I turned it down to 70 to prolong the life of the remaining LEDs. I strongly recommend to reduce the backlight intensity on LED TVs if possible! The most common fault of modern TVs (2013 and up) are faulty LEDs. The panels are constructed so sloppily (on purpose?) that a failure is inevitable.

It is ridiculous, if you think about it. LEDs replaced the CCFL tubes not only for economical reasons, but they also promised a longer life. The older Philips models for example proved that right, I have yet to see one with a failed LED, but the latest rubbish panels from LG and Samsung turned it upside down.

If the term planned obsolescence applies to TVs, the backlight would be my candidate. All other defects I've seen so far may be attributed to a lack of careful engineering, but those direct-lit LED backlights are around for over three years now, they die like flies and nothing has changed.

About LEDs

I have used this type: UNI LED

Problems: they have an opposite polarity and they are a little too big. They are more blue and shine a little brighter. I cannot tell for sure whether that is due to the aging of the original LEDs, but I assume not.

I think this type: JUFEI LED fits better. It has exactly the right size and the polarity matches. Due to its slightly higher forward voltage I assume it would shine darker. 

I am going to keep various types with both polarities on stock. They are cheap after all.

Backlight LEDs - types, sources, tools, techniques

Please note that the links to the Aliexpress shop may be invalid at any time. This shop sometimes has the LEDs, other times it doesn't.

Direct backlight LED strips

LED strips are a common technique these days. The outstanding Philips 42PFL9803 once had a huge number of LEDs in a matrix. See this post. Its image brightness and homogeneity were second to none. Nobody does that anymore. It is too expensive.

Size
The LEDs used for direct backlight are 28x35mm up to 35x35mm, thus their size code can be 3528, 2835 or 3535
.
Voltage
The smaller LEDs (2835 or 3528) are usually 3 volts, 1 watt.
The bigger 3535 types can be 3V 1W up to 6V 2W.
The size is not a sufficient criteria for choosing LEDs.

Polarity
To my surprise, not all LEDs are equal. All have a small and a large contact pad. However, the cathode (minus) and anode (plus) can be either one.
In the following text, I use

• L- = cathode (minus) on large contact
• L+ = anode (plus) on the large contact

When a LED with opposite polarity is used, it will not sit in the original center and the plastic lens has to be offset from its intended place. This can cause difficulties with the homogeneous light emission and the repaired LED might get visible on the screen.

Contact shape
Some types can have S-shaped contacts. They will not fit on rectangular-shaped solder pads and the other way round!

In the following text I use

• S = S-shaped
• R = rectangular shaped

Top marking
Also the top marking does not reliably indicate the cathode, like it would be with ordinary diodes. Manufactures do as they please.

3V Types

Lextar 3030 3V 1W shape R, polarity L-

I found those in a Panasonic TX-P55DXX689. The image is that of a defect LED, I have not ordered any of them, yet. The dent at the right edge is normally not there, I did that.

Samsung 3535 3V 1W shape S, polarity L-

JUFEI 2835 3V 1W shape R, polarity L-

SEOUL 2835 3V 1W shape R, polarity L+

LG Innotek 2835 3V 1W, shape R, polarity L+
Identical parameters and light as the SEOUL. I think those are the original LEDs in the 50LN5406, for example.

UNI 3535 3V 1W shape R, polarity L+

LUMENS 3535 3V 1W shape S, polarity L-

6V Types

SEOUL 3535 6V 2W shape R, polarity L-

LG Innotek 3535 6V 2W shape R, polarity L+

SHARP 3535 6V 1.2W, shape R, polarity L-

How to know the most popular LED types

If you like to stock up on LEDs and don't know where to start: go with the masses. See what others have bought:

Most popular LEDs

Testing

The best tool I know is the LED backlight tester from China. It is available on Aliexpress, here for example: Latest (model GJ2 C) backlight tester. It is a real time saver.

There are older models (GJ2B) around, which are cheaper.

As of end of 2016 the number of different tester model has increased. I can only speak about the aforementioned model. It is fully automatic and adjusts the voltage by itself. It tests a single LED in one moment and a full panel right after that. Tester with a potentiometer where you have to adjust the voltage yourself are much too inviting for user errors.

This design is also available as a high voltage (>1500V) CCFL lamp tester: Lamp Tester

Soldering

For my first LED repair I used a hot air gun. That is ok, when you keep the temperature low enough to avoid melting the transparent plastic. However, swapping the LED would be much quicker if the solder on the strip were molten while pulling the old LED off and putting the new one on.

Shop Jimmy presented a LED rework station on YouTube once. It seems as if this very cool and cheap gadget is out of stock. They have blocked access from outside the US, so I cannot tell for sure. While looking for an alternative on AliExpress, I found the KADA 853B preheater:

It is basically a hairdryer in a box. It is a rough little machine. It vibrates like hell, because they did not decouple the noisy fan from the case. I guess I'll have to do that myself.

It is not powerful enough to heat a multi layer PCB with large ground planes quickly up to the melting point. I tried that on a small TCON board. They call it a BGA preheater, which is ridiculous. You will not want to solder BGAs with a device that has no temperature profile!

As it turned out in my first LG backlight repair (see this blog post), it was not possible to melt the solder in acceptable time with the device. Nevertheless it is useful as a preheater and with a little support from a hot air gun, soldering LEDs is very quick and not stressful for the LED.

LG 50LN5406 - flashes shortly - LED backlight defect

I finally got my hands on one of the LG trouble children. The TV flashed the LG logo very briefly and then switched off again. The seller had a repair shop diagnose it and they said that the LED backlight was broken. Their repair offer was 320€. Wow. That's more than the used price of this device.

The LG of this age all die sooner or later due to one or more dead LEDs. The backlight in standard setup is too aggressively set up and they overheat.

I did not bother measuring anything and went straight on to a backlight repair.

Back cover off, nothing spectacular to see:

Step 1: Remove the front bezel:

Step 2: Unscrew the metal panel bezel, unplug the flat cables from the TCON board and carefully slide the buffer boards out of their seat:

Step 3: Remove the panel. This is the most delicate part of the operation. A 50 inch panel bends a lot when not handled correctly. I always wear gloves to avoid finger prints. Do not force a blade or similar objects between the panel and the frame to get a grip on the panel! A simple trick is to first unclip the black frame, raise it a little and then reach under the panel. That way it is easy to lift the panel with one arm diagonally supporting it from below and the other hand holding one edge to keep bending under control.

Be careful with stuck buffer boards. Make sure they slip out without force.

Step 4: Remove the panel frame and the foils. This is simple. Just wrap a tape around somewhere to keep them together.

Step 5: Remove the reflector sheet to get access to the strips. The four plastic standoffs come of easily when you squeeze them with pliers from the backside.

Okay. Measuring time! A good strip settles at 27.4 Volts. The bad strip yielded 36.1 Volts and it was obvious why. One LED was dead.

I removed the right half of the strip with a spatula, taking care of the double-sided adhesive tape, which will be reused.

Now, my new preheater got something to work on. The plan I had was to heat the strip up until the LED's solder would melt. Nope, not working. The material is too thick and a large copper trace shielded the heat from the top. Anyway, the lens came off very nicely under heat. The LED was so heavily damaged that it broke into crumbles. I removed what was left of it with the iron.

This looked terrible. The cathode pad was burned black all over. It almost seemed as if the soldering went wrong on this one and it heated up too much.

I cleaned it with a fiber glass pen and some Isopropanol:

This looked much better. Next time I will remove the sticker, too, before I work on the LED :-P

The SEOUL 2835 3V 1W fit perfectly. I put some leaded solder on the pads and the strip back on the heater. With just a short heat shot from the top with my heat gun at 260°C the LED snapped into place by itself on the molten solder.

Click here to buy the original LEDs. The LG Innotek LEDs perform identically to the SEOUL, but some might feel more comfortable with the exact match.

I glued the lens with plastic glue. Super glue did not quite do the job.

And here we are, all shiny and new! The new LED was indistinguishable from the others:

Evangeline Lilly is looking happy!

What to do to prolong the life of this TV

Turn the backlight intensity down to 50%! The image is still good enough and the LEDs are substantially less under stress.

My lab instruments for testing and measuring

A list of my favorite gadgets for testing my TVs and other devices

Keithley DMM6500

This thing is awesome. There is no other desktop multimeter in this price range with such sophistication. It is super fast and precise. The display is great. It has a touch screen. The continuity test is just perfect (very important feature!). It's best part is the digitizer, which can record voltage or current measurements on a fine-grained time axis. This is fantastic to analyze transients or flaky behaviour of devices when switched on. A scope in rolling mode might do that as well, but the Keithley gives you zooming and all the number statistics. However, setting up the trigger for such measurements is nothing you just do. It requires reading the manual. You can program this thing for specific test scenarios. I've never done that so far. My stuff is rather easy to measure.

EDS CapAnalyzer 88A v2

This tester is in its own league. There is nothing comparable out there. EDS does not build their brilliant testers anymore, like the EDS LeakSeaker, which I recently got as a DIY kit and built it. I was delighted to find the CapAnalyzer on eBay from an authorized seller, who builds them from the original plans. It measures caps in-circuit. And it is resilient against charged caps! None of the testers out there have those properties. They would just die exposed to a charged cap. Look at some videos on YouTube. 

Doing a super quick routine check of all the electrolytics in a device is now possible. No soldering, no speculation by the looks of things. It is emitting beeps according to the outcome of the measurements, you don't even have to look at it while testing the caps one by one! Absolutely brilliant, designed by a real engineer who knows his shit.

It's quite expensive though (and it looks kinda ugly...when engineers design things...), but it is one of those gadgets which you will have for a lifetime.

Update: In the meantime, I got myself a Peak Atlas ESR70 (see below), which is more sophisticated in some aspects, but you can't control the DCR level on that one and it does not have a nice scale for quick assessment.

EDS LeakSeeker 89

Another unique device from EDS. So far, nobody has built anything similar. I put mine into a larger case so that it can be powered by two 9V batteries.

Read all about the build HERE

Grundig RT5A

My trusted companion! Has my back during repairs with exposed "hot" power components like in SMPs. I hovered over eBay for quite some time until I found one in perfect condition.

GWInstek PST-3202

I bought it used from eBay in mint condition for a fair price. It is prohibitively expensive when new. Technically it seems to be a very good supply with sophisticated circuitry. No simple one-chip regulators here, all proprietary stuff with AD-conversion and processor control.

From the usability side, however, it has some drawbacks:

• The fan is annoying. I already replaced it with a more silent model and put some foam on its frame. The reason for the noise is the speed control, which does not apply a linear voltage, but a pulse signal. This makes it efficient, but the motor engine answers with noise for every impulse.
• The display is hard to read. The plastic screen is a little opaque and that renders everything fuzzy. Silly idea. Later models have a brighter, white-on-blue display, which might mitigate this a little.
• The rotary knob doesn't work well with one finger.
• The terminals are only banana sockets. (Fixed in later model)

QJE QJ12001X

I bought this supply because it goes up to 125V, which is quite useful for LED backlight tests. Apart from that, it is a basic device. When I only need one simple voltage I prefer it over the GWInstek because it is easier to fire up quickly.

QJE PS2002H

This is a brilliant device. A fully equipped supply as big as a multimeter, which does 0-30V and up to 3.75A. As I do a lot of repairs outside my lab, this thing is extremely useful. I did a stress test under full load and it got merely hand warm. Apparently, the switching circuit has very good efficiency.

Be aware! In Komerci's shop at eBay, you get it for 100€. It is also sold under the brand Velleman for twice the price. As of today, this is the only one of its kind.

Unfortunately, it broke down one day without any reason, not even being under load. I swapped the PWM chip and some Opamps with no success. Bought a new one, it is just so useful for repair jobs outside the lab!

Cirtest 3000E

This is my oldest gadget and I love it. I got it as kit from an uncle 35y ago. It is a continuity tester whose tone pitch depends on the measured resistance. It is indestructible due to clever (patented) protection. It won't even mind plugging into the mains. I have used it a lot. It is ideal for super-quick A/B checks and finding connections or shorts on complicated boards. Just sweep over the pins and listen. It also reveals bad (relais) contacts or potentiometers with ease. They will make an unstable or crackling sound.

I think the same circuit is used in the CONTITEST 4000 devices, which come in multiple variants. There is a very decently priced kit: CONTITEST 4000 Kit.

BKPrecision 390A

My workhorse. I am very happy with it. I chose this model because it can measure capacitance up to 20000µ. Very useful for measuring audio equipment.  

Annoyances:

• It beeps with every action I take  The beeping is ok when the test leads are in the wrong sockets, but I really don't appreciate it for anything else.
• The very small "m" symbol for mV or mA. I did overlook that a number of times. There would have been plenty of space on the display for a bigger symbol. 
• The min/max mode is confusing me every time. The thing beeps at me and I don't know why until I switch back and forth to reset it. I am never quite sure whether I did my measurement correctly.

Defects:

I had to clean the switch once because the diode and continuity modes were not reliable anymore. No big deal. Contact spray and polishing the contacts with paper did the job.

Voltcraft R200 milliohm meter

With this meter, you can do four-pole Kelvin measurements in the milliohm range. The device also measures voltages, current, diodes, and capacitors up to 10000µF. I got it used on eBay. I did not work properly out of the box. It would signal a weak battery although they were all brand new. Also, the display appeared weak. I spent some time digging into it, expecting to find some contact problems, until I identified a bad capacitor in a charge pump circuit. No big deal to fix.

The exact same meter is sold also as PeakTech 2705. It depends on your color preferences :-) However, the Voltcraft manual is written much better.

Kelvin measurement at work. A short piece of wire in the milliohm range:

With its six AA batteries, which are required for the 200 mA test current in the 4 Ohm kelvin test range, it will run forever. I am going to use it for my mobile repair sessions instead of the BKPrecision. It is rugged and it only has one (+) socket for V,A,R and C measurements. Might not be the safest solution but it sure is convenient.

The kelvin clips are too clumsy for tracking down shorts on boards. I am planning to build single probes with two wires each. For shorts tracking I don't need absolute fidelity. It is sufficient to have the provided resolution as it is just a matter of comparing values. The lowest value identifies the hot spot.

Blue ESR Meter by AnaTek

Indispensable for testing capacitors. Robust against residual voltages, it can even measure the inner resistance of accumulators to check their quality. I bought it as a kit and had no problem building it. The scale I found in the net and glued it onto the case.

DUOYI DY294 Transistor tester

This is an exotic yet useful device and it is one of a kind. It can measure breakthrough voltages up to 1000V and as a transistor tester it measures the amplification factor. It drives the device under test with higher voltages, which reveals defects under load that are undetectable by any other tester.

I lately found a broken, innocent-looking 1N4148, which measured perfectly ok with the multimeter's diode mode, but had a reverse breakdown of 29V! A good one has around 140V. The only test instrument that could reveal this was the DY294. Worth every cent (it is cheap).

It can also test three-terminal voltage regulators.

BSIDE ESR02 Pro component tester

There are many variations of this tester design on eBay or Aliexpress. The makers of this particular variant had put more thought into the user interface. There is a discharge terminal to the left. There are nice SMD pads, a terminal to plug in wired components, and even little slots where to put SMD parts. After calibration (read the manual, for once :-) it is actually very accurate. Its display is not as pretty as in other models, but who needs colors to display a bunch of numbers?

And it is dirt cheap. A must-have.

LED backlight tester

I watched a video by Shopjimmy where they used this tester to check LED backlights. This was so convincing that I had to get one to be prepared for the increasing number of backlight defects in TVs.

It can generally measure the breakthrough voltages of any single LED, but is also powerful enough to drive LED stripes or even the whole panel and that makes it a brilliant time saver. It produces over 300V if necessary. It comes with needle-pointed probes, which are able to pinch through the plastic coating of LED strips to test individual LEDs if necessary. Nice.

It is available from Aliexpress or eBay for little money. Watch out for cheaper, older versions. I have revision C.

Vellemann audio signal generator

This handy little generator is available as a kit. It produces a sine wave in four steps from 50Hz up to 20kHz. It covers all relevant frequency ranges in audio equipment. The output voltage level is tunable with a potentiometer.

DIY signal tracer & amplifier

I built this with a simple integrated amplifier chip and a DC-blocking and over-voltage protection front-end. It can be used as an active speaker or signal tracer. It runs on a 9V battery. Indispensable for testing all kinds of audio equipment.

DIY transformer ring tester

AnaTek also offers the Blue Ring Tester. This device emits a pulse and counts the damped ringing of a transformer's coil. Each count represents one LED starting with red. It can identify shorted or open transformers or inductors, respectively. I need that so rarely that I decided to build it myself hand-wired instead of buying the kit. The circuit diagram is available for free on the net.

Statron 3229 electronic load

This is one of the gadgets which are sometimes invaluable when you build or test power supplies (like I do). It can be configured to present a constant current load or a constant resistance. Electronic load devices are very expensive when they are programmable. This one isn't, yet good enough for me. You need to use a power supply or a multimeter to adjust it.

The only complaint I have is that the adjustment knobs "fine" and "coarse" are swapped in the constant R section. That's just silly. Apart from that, it is quality engineering made in Germany.

Hantek DSO 1062S

This was my first digital scope. It is portable with a built-in battery, which was the primary requirement for my mobile repairs. Running on battery also has the advantage of being decoupled from ground.

The user interface is somewhat clumsy and takes getting used to. It does a good job with the measurements I do in TV power supplies. It is hackable and mine goes up to 200Mhz instead of the original 60 :-)

It has a multimeter mode, too. It is not a digital storage scope though.

Rigol DS2102A

I had a repair case where I just couldn't figure out what was going on because everything happened so quickly. That motivated me to get a true digital storage scope. For testing power up/down and glitches issues that's the only tool that helps. This thing can do way more than I will ever need or understand. For the occasional user it is actually pure luxury, but well, hobbies, what can you do? :-)

In the meantime, I was able to find a hack so that it has 200Mhz bandwidth now and all the demo features enabled. Pretty cool.

Peak Atlas ESR70 gold & DCA75

During my final build of the EDS leak seeker, I realized that outstanding test equipment is not here to stay forever. One has to get it while it is still available. Therefore, I purchased two of the Peak Atlas gadgets, although I had both measurement tasks already covered.

Peak Electronics to me looks like one of those small companies with a few clever guys, which might not exist anymore in 20 years or so.

The big advantage of the ESR70 over the EDS cap tester is that it measures ESR and capacity, even in-circuit. This simplifies component diagnostics a lot, as sometimes an electrolytic cap's ESR seems fine, yet it could have lost its capacity.

The DCA with its USB connectivity can draw transistor curves, which tells you more about a component than a simple tester does. I will have use for that someday :-)