Marantz SR7007 - not starting - rapidly blinking LED - defect transistor MMBT5551 in ASO protection circuit

I always wanted to peek into an AV receiver even though I know that these devices are notoriously difficult to service due to their tight packing of boards. But sometimes, we just need challenges, right?

The SR7007 caught my eye on eBay. It is still a quite young model (2012) and is technically mostly identical to the 08 Series of 2013. I need preamp outputs and this one had all channels. Nice.

When I switched it on, I heard one click, the display went on and then after about three seconds it switched into protection and the LED blinked rapidly about twice per second.

I suspected a problem with the power amplifier because after the delay normally the speaker relais should switch. Knowing nothing about this device I first tried my luck by isolating (aka plugging off) parts of the power amp board. I got lucky by pulling the high voltage supply. The receiver started and switched the relais after 3 sec. I found nothing suspicious on the power transistors. They all measured identical. Neither did I see any burned parts.

I studied the thing a little more and identified a cable with five lines as the protection signal cable, which goes to the main digital board.

When I pulled that, the receiver would again go into protection, albeit with a different blink code (1x per second).

Now it was time to get the service manual, which is only available for money. 12$ is not a bad price, so I got one and it proved to be worth every penny.

With the high voltage unplugged from the power amp board, the device could be booted in a diagnostic mode where it displayed the last protection error. After the steps in 3.2. shown below, you have to press the Status button on the device. The description is somewhat confusing.

I did that and I got this:

For ASO (no idea what this means), the manual states the following:

Now that did not make any sense. The receiver had never switched the speakers on and neither was there any speaker connected. However, it pointed me to the direction of the ASO protection circuit. Something had to be wrong with it.

Q7001 does a logical OR on all ASO signals supplied by the 7 power channels ASO circuits. The collector signal goes straight to the digital board:

The red line is high voltage plus. It made perfect sense that when this voltage is missing, the ASO protect signal would not go to the digital board. I confirmed through measurement that the transistor switched on during boot. So at least one of the channels must have had a problem.

Now about the actual ASO protection circuit (here: surround back right channel). The marked transistor senses excessive current and when switched on, R7744 passes a plus signal on to Q7001 on the previous image. This circuit is identical in all 7 channels.

The inconvenience was that all the parts for the protection circuit were on the underside of the board. The unit is easy to remove, that was not bad at all. I decided to bend the legs of the power transistors to get access to the underside. Better than unscrewing all of them (horror!)

Now I checked all those 22k resistors, which go from the sensing transistor to the ASO switching transistor's base. And lo and behold, one was off by 3kOhms. The surround back right channel had a problem.

The only possible failure could have been Q7739, the sensing transistor. It measured ok with the diode tester, but it showed a lowered resistance between C and E. I unsoldered it and presto, the resistor R7744 measured normal again. My transistor tester did not recognize the MMBT5551 transistor at all. It showed me two resistors instead.

It is the little guy in the center of the image:

I replaced that sucker and the device went back to normal. A cheap fix, time-intensive and very rewarding. I learned a lot. I always like to improve things after I have fixed them, but in this case I didn't come up with anything. It is hard to tell what happened here as the power stage was still in good shape.

While I was at it I took the chance to adjust the idle current of the power stage as well. It is nicely documented in the manual. The SBR channel was off the most. Was that a coincidence or some further symptom of  the incident? I don't know.

About the Marantz SR7007 in general

I never had an AV receiver and I was curious how it worked. Well, the sound is considerably worse than my highly modified Benchmark DAC2, which feeds Focal SM9 active speakers. That was no surprise at all. I have seen its guts and I knew.

What did disappoint me was the image quality via HDMI. One might think that digital signals will not get compromised in digital processing. Not true. The passed-through image definitely lost sharpness to a degree I don't accept it. So that was no option. I am watching movies via my PC and its optical output worked well with the receiver.

The serviceability is not so bad, really. The service manual is very good. The boards, which have the highest expected failure rate (digital board and power amp board), are easy to remove. I think none of the receivers have a bottom lid anymore for an easy checking of the power transistors. They replace whole boards these days and don't mess around.

Replacement of Panasonic Plasma parts (DAF30, 30F131, RFUH25, DG302, RJP30H2A, RF1501N)

The original Panasonic parts for the NeoPlasma series 30 and 50 are slowly going extinct. As I am a big fan of those devices, I was spending some time to find alternatives. I was able to source all parts either from AliExpress or DigiKey.

The parts listed here are susceptible to failure on SC or SN boards, respectively, and SS boards.

Use this information at your own risk! This is my result of doing research and experiments. So far, all of the Plasmas I have fixed are still running fine after 1-2 years. If the parts were fake, they would have blown up after a short time.

You can never be sure whether a chinese seller has the same quality parts on stock after some years. Take my tipps as a starting point. I wrote this article in early 2017.

New Kid in Town? TGD40N40P

I found yet another potential alternative to all the IGBT transistors: TGD30N40P.

This type is manufactured in Korea and is around since 2012 according to the datasheet. I will test them soon. Stay tuned.

I think that the small number of sources on Aliexpress is a good sign. The market does not yet seem to be swamped with crap copies.

IGBT Transistor GT31F131

Can be replaced with FGD4536. That I know for sure, because I fixed a TX-P50GT30 and a TX-P55VT30 with those successfully. Alas, this device is also discontinued.
My source has dried out. Stephen Foxall found a legit source HERE.

IGBT Transistor DG302

Datasheet
This transistor seems to be the strongest in the bunch. 250A peak and 40A continuous current. It's good to have a bunch of them on stock. I don't know any exact replacement for this one. It's the gold nugget of the circuit.  The FDG4536 might be a viable candidate. It is difficult to tell because the interval for the 250A peak current is not specified in the minimal data, which is available for the DG302. The FGD goes up to 220A for half-sine, pulse-width 1µsec and its switching times are even lower than the DG's.

In the meantime I have tested a 42VT30 with the FGD instead of DG and it runs perfectly fine. The FGD run at around 55°C with the original heat sink glued on top and that is totally normal.

I am happy to finally share a source of legit DG302 on Aliexpress! They measure exactly like the originals and one did work flawlessly recently in a 42VT30. 

IGBT Transistor RJP30H2A

Datasheet
Again, I fail to see the distinctive difference to the DG302 und 31F131 besides the 5A less collector current. I recon they could have built the whole thing with DGs exclusively. This type isn't used in the 50 series anymore. I have replaced them successfully with FGD4536. Even Panasonic uses an 31F131 instead in the scan board of the TX-P55VT30.

Generally, the problem with the data given in the sheets for the maximum  pulse current is difficult to compare as the manufactures use different pulse lengths. The F131 is rated for 3µsec, the DG302 datasheet doesn't tell anything about it, and the FGD4536 is rated for <1µsec. This leaves the hobbyist with trial and error as the only option.

Diode DAF30 (DA3DF30A)

Datasheet
Can be replaced with STTH20R04G. The datasheets are a perfect match. If you want more juice, the STTH30R04G will deliver it, it's a monster diode. I recently used STTH20 twice as substitute and it runs perfectly fine with normal temperature.

A STTH30 recently also worked fine in a 42VT30.

Diode RFUH25

Datasheet
Why Panasonic is using this diode alongside the DAF30 is a mystery to me. The specs read the same. Maybe there is some subtle detail I don't understand. I think the STTH will fit here, too.

Diode RF1501N

Datasheet

And yet another diode, which looks the same as the others. From the specs I cannot see any significant difference to the DAF30 and RFUH25. The DAF is a few nanoseconds quicker at recovering. They are dirt cheap and available from DigiKey or Mouser or even cheaper HERE on Aliexpress. The chinese source is legit. I have tested and used the diodes successfully.

Control Chip BD8639FVM (SMD Marking D86)

Bought some from THIS source without problems. Update: has been reported to have become a bad source.

Driver Transistors CPH5524 (SMD Marking 3Y)

Bought some from THIS source without problems.

Dell 2709W Ultra Sharp - blue power LED constantly on - unresponsive - main board reflowed

I have a DELL 2410 and I like it a lot. When I saw the defect 2709 on eBay for a reasonable price, I thought I could try a monitor for a change.

The defect showed as follows:

When plugged in, the blue power LED came on immediately and none of the other buttons reacted to touching. The device was totally unresponsive.

In this thread on Badcaps I learned that reflowing the main board revived some of the sets. Before that I did my voltage check routine and found nothing suspicious. The 23.5V were there and all the secondary voltages looked good as well.

The right chip under the heat sink was warm, the left was stone cold and its clock wasn't oscillating. It seemed as if the right main BGA chip would activate the left after booting.

So, my brand new reflow controller got something to prove its value. It is a clever device, which controls a normal el cheapo pizza oven precisely via a feedback sensor, which I taped directly on the BGA chip.

Before I ran the standard profile, I poured some liquid flux under the chip. I don't know if this had a part in the success, but I thought it wouldn't hurt.

And voilà! The monitor ran flawlessly again. Hallo Frau Johansson!

During my research I came across an interesting software, which is able to reset the factory defaults in a monitor. It's called softMCCS and is available here: http://www.entechtaiwan.com/lib/softmccs.shtm

It identified my two monitors. First, the defect 2709 would be found, but DDC/CI was marked as "not supported". After the repair, it read "supported". So this is a nice tool to check whether the processor is working ok or something else is broken.

Rest in Peace

14 months later the error came back. A second reflow did not fix it. I also learned that the larger electrolytic capacitors did not like the oven heat. They were bloated afterwards. I'll remember that for my next reflow task.

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.

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.