Fake chinese GT30F131, RJP30H2A under the microscope

In this blog I reported my experience with a chinese supplier. I came to the conclusion that both IGBT transistors were fake by measuring and visual inspection. Let's put them under the microscope!

First, the original RJP30H2A. Notice the extra notches to the left and right.

Now the fake. The notches are missing and the character font is different. Also, there are traces, which look as if the package has been sanded to remove the original marking and re-labeled.

The 30F131 original. Everything is crisp and precise.

The fake shows very strong signs of sanding and the labeling is sloppy and imprecise.

The 30F131 may look different, depending on the batch. The imprint "MX 18" and larger character size are actually valid, but the overall quality is just ridiculous.

For the images I have used the Andonstar A1. It is a decent device for its price.

Panasonic TX-P50GT30 - 7 blinks - TNPA 5335 y-sustain - FGD4536TM used instead of 30F131, RJP30H2A

I love my GT30 and when I found another one on eBay I grabbed it. It had the same 7 blink disease. See my earlier blog post about all the details.

Due to my disappointing attempt (see this blog post) to get some genuine IGBT transistors (30F131, RJP30H2A) from China, I settled with the FGD4536TM instead, which was mentioned in various blog posts in the Badcaps forum.

I got the FGD from DigiKey. They are already discontinued and not on stock at Mouser anymore. It is a good idea to order a large batch. As plasma TVs are not manufactured anymore, this type of device becomes obsolete.

As you can see, the FGD are much smaller. The RF1501 in the center also came from Aliexpress and it is genuine and working ok. The DAF30A on the far right came from a scrap board.

I also ordered a STTH20R04G-TR diode from DigiKey, which might replace the difficult to get and fake-prone DAF30A someday.

I also tried something new to resolve the loose screws problem. I observed that the screws, which have an extra bracket were perfectly solid when I unscrewed them. Why? Because they had no solder under them which floats under pressure. So I cleaned the critical one next to the DAF30 diode and some others, too.

The most popular suggestion is to use spring washers. I did that too in my previous repairs, but I think the remedy is simpler. The thing with the washers is that you need longer screws, which must not be too long to avoid drilling them into the panel.

Currently the device is running its burn-in. The FGD IGBTs have settled at around 48°C at 22° room temperature and open back cover. This is roughly the same temperature as the three 30F131, which are left on the board. Some say that the FGD run cooler. I cannot confirm this.

I'll also watch the screws. I left some with solder on the holes to have a comparison to the cleaned ones.

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.

Philips 48PFK6409 - no standby LED - fell asleep by itself - revived with on-device "ON" switch

This must have been the weirdest case I ever had. I did not bother publishing it first. But after I was able to help with another case about a completely different Philips model (42PFL6008K) in the Repdata Forum, I thought I'd share my experience as it seems not to be such a rare problem after

all.

The symptoms are:

• Device suddenly stops working and would not switch on via the remote.
• Unplugging does not help.
• The standby light will not light up when plugged in.

The solution is: RTFM! I opened the device, measured all the way through it and found nothing. However, in the schematic of the power supply there was this ominous "ON" switch. I could not find any switches on that bugger. So I consulted the user manual.

And here is what you need to know:

So, are the users too stupid? Of course not. The TV obviously switches itself to a state as if the user pressed the button on the device himself, which he never did! The chain of cause and effect is not understandable and the user is left clueless, suspecting a defect.

We all have experience with device buttons, which are mirroring the function of remote control buttons. The on/off button on the device would do the same as on the remote. Not the case in those Philips models! The TV can be switched off to consume a minimum of energy. So it has three states:

"low energy sleep" <--> press button on device <--> "standby" <--> press remote on/off <--> "running"

Unconventional power supply architecture

The power supply did not have a dedicated stand-by circuit. Instead, the 12V output is throttled down to 6.3V in stand-by and some downstream regulators took care of the rest.