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2017-06-19

Reading Philips TV logs with an USB-UART adapter

With my Philips TVs I never had the requirement to read the log, as they all had measurable faults or the Service Default Mode revealed everything I needed to know. In case of a two blinks error code, which points to the mainboard, or when the TV won't boot at all, it can be beneficial to peek into the log.

You need

  • An USB-UART Adapter. This device maps a serial  (UART) connection across USB to a serial port (COMx on Windows). Device drivers are required.
  • A terminal program, which can handle serial ports.

The hardware


There are various types of USB-UART adapters on the market (eBay or AliExpress). First I tried this type:

Those are garbage. They contain an illegal copy of a Prolific PL2303 Revision A chip, which is discontinued since 2012. Read HERE. The problem is that the latest Windows 8 & 10 driver won't work with it anymore. Some articles in the net say that Prolific has changed the device signature in their later revisions to lock out the copies. You need to install an older version of the driver. I wasted way too much time with this rubbish.

I opened mine up and the chip had no marking on it. Sure sign of a copy. Also, the USB plug already started to come off the board.

So I tried another one with the Silicon Laboratories CP2104 chip:


This one's legit. No driver problems, Windows found the driver itself and the device worked.

The software


On the PC you can use PuTTY. A more sophisticated program is RealTerm. It can record sessions, which is quite useful, and has more features than you'll ever need. Both are free.

The Android app Serial USB Terminal by Kai Morich also works fine. You can read the log on your tablet or phone quickly without a bulky laptop. Just put a micro USB adapter in front of the UART device.


The connection


Now this kept me busy for a while due to my own incompetence.

The UART / service socket on the TVs is a stereo 3.5inch type like for headphones. The connections are as follows:


Here is the rub: you need to cross RXD and TXD. Don't connect the RXD on the adapter with the RXD on the TV. Makes total sense once you understand it :-)

A schematic from a ComPair device manual put me on track:


And that's how I built the thing. I attached a 3.5 inch stereo socket to the adapter and used a stereo cable I had lying around:



First tests


I had a working 42PFL9803 sitting in my living room and I tested the device with it. To my surprise I could not get any useful log. The service manual says 38400bps 8N1. I configured everything accordingly and all I got was garbage. The TV sent data but it wasn't readable. I tried many bps setting with no luck. This TV fooled me for quite some time. I thought something was wrong with the UART adapter :-/

Yesterday, I picked up a 32PFL9606 and with this one it worked flawlessly. I don't know what's wrong with the 9803. Very strange.





Sweet! I can add one more diagnostic tool to my repertoire. I currently have a 46PFL8007 with the dreaded QFU chassis, which doesn't show any signs of life even though the standby voltage is good. It's not writing a log either. But that's the subject of an upcoming blog post once I have reprogrammed its boot EEPROM, which I suspect.

2017-06-05

RUNTK5351 TCON - defect analysis - ISL98602

The TCONs with the ISL DC/DC chip notoriously go bad. Sometimes they are fixable by swapping the chip, sometimes they are not. I had the chance to play with four broken boards. Two of them got a new ISL and still didn't work. However, I present you a few tips how to avoid fruitless work, because the main video chip may be measurably dead. Also I think I have measured the reference voltages that the ISL should produce.

The next image shows the voltages of a good ISL chip:


If the voltages are all there and there is still no image, the main chip is dead.

Normally though, the TCONs come with an ISL, which produces no voltages at all. Here are the tests you can do to asses whether it is worth changing:


  • Test 1: In diode mode, measure the breakthrough voltage of the 1.2V trace. It should be around 0.5V. If it is 0, forget the board.
  • Test 2: Attach a lab power supply with 1.2V and current limit around 100mA to the 1.2V supply. The main chip should draw about 0.01A. If not, it is broken.



Alas, I did not yet have a working board in my hand to know how much current the board is supposed to draw from the 12V line. The ones with the fixed ISL and no shorted main chip both pulled 0.39A. The main chip got pretty hot quickly. I guess this is not normal.

Changing the ISL

This is very difficult. I never managed to solder it properly with hot air only. It always took me an extra step with the soldering iron to get the solder to flow at the pins. I failed with a needle tip. It doesn not have enough heat capacity. Spade tips neither worked, even small ones, because they all were too clunky to reach the pins. The only tip that worked was the horse shoe with an excess amount of solder on it. A perfectly rectangular tip would be best. And lots of flux is required, of course.

Be extremely careful with the microscopic SMD parts around it, especially on the upper right corner (previous image). That one 0 Ohm resistor close to the edge gets pushed away easily.


2017-05-25

Philips 46PFL8007 - QFU1.1E LA - no standby LED - main processor dead

This is a short story with no happy end. I bought this Philips as defect and didn't ask any questions. The description said it wouldn't switch on anymore. Well, that did not sound so bad. I had fixed another QFU1.1 this year with a dead standby supply.

At pickup the seller told me that the TV had been fixed during warranty with the same symptoms. The main board was the culprit then. Uh oh...

When I plugged it in, the standby LED did not light up. Standby voltage was present. The LED is controlled by the main processor (the standby processor section). The only voltage the stdby proc. takes in is the 3.3V standby. Nothing else. The LEDs are fed with the same voltage.

I studied the service manual thoroughly and the only conclusion was that the processor was in trouble. I ran a reflow session in the oven as a last resort. Did not help. It is actually dead!

So, if you get your hands on a QFU1.1 chassis device with no standby light, there are chances that the main board is hopelessly broken. They are very hard to find, so don't bother!

Update


In the Iwenzo repair forum I got the hint to reprogram the standby software flash ROM. For that you need two things:

  • The software binary for the QFU1.1 platform. I found it in a russian forum. It is not available from Philips.
  • An EEPROM programmer. I ordered one from AliExpress. This will take a couple of weeks.

Also, I am going to investigate how an UART-USB adapter can be used to read the boot log. This will be interesting.


2017-04-02

Panasonic TNPA5330 SN board 7 or 6 blinks - detailed fault analysis and repair guide (TX-P42GT30, VT30, ST30)

I received a TX-P42GT30 with the famous 7 blink disease and it is the fifth Pana plasma with this defect. I am going to present my analysis of the causes of this defect, which appears after four to six years. On eBay I am seeing more of them these days.

The actual cause are loose screws. Why did they get loose? Because of the solder on the contacts. Solder is soft and flows under pressure. Why is this troublesome? Some screws and their contact pads conduct a lot of current into the metal panel chassis. When they become loose, the contact resistance increases and sparking occurs. This in turn leads to very high current peaks, which eventually kills (shorts) a diode. It is also possible that the increased resistance causes the mounting area to heat up and that kills a diode. This diode connects six transistors and another diode and those die immediately.

The next image shows the troubled screw position in close-up. It takes the full current from the DAF30 diode to the panel chassis ground. Other screws, which I'll show you below, pick up the current and from there it flows back to the power supply. Notice how the legs of the diode are discolored through heat! This one got enormously hot:


The mounting hole backside under the microscope. We see blackened, burnt solder:


And this is what a mounting point looks like:



As long as the screws stay under tension, the contact to the chassis will be good.

In the 60 series, Panasonic has learned from the screw disaster. This is an image from a 55STW60. No solder on the holes and screws with spring washers!


They also finally stopped using SMD power transistors and returned to decent heatsinks. Who needs silly super-flat TVs, anyway? I think those scan boards are built for eternity - maybe, provided the capacitors, which get all the heat from below, are holding up well.



In the next image, I marked the other screws, whose holes also had burn marks. The two on the top pick up the current from the chassis, which enters through the screw in the center. You see the already repaired board with my choice of transistors and diodes (see this post). Other screws have a proper bracket on the board or don't carry much current. There, the contacts looked ok.


And here is the section of the circuit where you can see all the affected high-power parts in one glance. The DAF30 diode is marked yellow. The diode and three transistors to the left and the three transistors to the right next to the troubled diode are all shorted when disaster strikes.


From 7 blinks to 6 blinks


6 blinks indicate a problem with the MIR voltage, the energy recovery voltage, which builds up across the blue C631. It must stay in a corridor around 120V.

Dead driver transistor array and control chip (energy recovery H section)
Strangely, a driver transistor plus its control chip die, even though they are not responsible for any of the shorted power transistors. Q441 is still ok, yet those two are dead. I wonder why, but I have observed this twice already, only in 42 inch models though.


Broken IGBT (energy recovery L section)



The boards I have repaired also had a less obvious failure in Q451, a DG302 transistor. It has no dead short, but in diode test mode, it will leak between collector and gate and show a break-through voltage on the multimeter. It may not have this fault at the beginning and develop it once the other defects are repaired and you switch the device on for the first time! But don't worry, it will not destroy any other parts. It is best to routinely replace it.

See also below where I describe how to debug the recovery section.

How to repair this defect properly

  • Replace all broken components
  • Remove all solder on both sides of all screw mounting holes. Only apply a very thin and flat(!) layer of solder. It helps making a good contact.
  • Clean the mounting points on the panel chassis from all black residue.
  • For the screw next to the DAF30 diode and the two on the top, replace the original screws with ones with a spring washer. Make sure they are not too long, otherwise you will drill into the panel! The screws will not loosen much once the solder is gone, but for the critical ones I want extra safety.

Debugging the 6 blinks of the energy recovery circuit

Through my own stupidity I damaged an already repaired board and spent hours trying to find the reason for the 6 blinks. The device started, the green LED on the SN board briefly came on and then it immediately shut down. Not enough time to take measurements with a voltmeter. A not 100% working driver transistor was the culprit. Along the way I learned a lot about the circuit.

Get the manual for the TC-42GT30 from elektrotanya.com. This manual is top quality with zoom-able schematics. Page  69, chapter 12.27 SN1 Board Schematic Diagram. I have another for the TX-42 with pixelated graphics, where you can't read the part numbers.

The recovery voltage can be measured across C631. It should be around 120V. The protection activates below 36V and above 157V. The polarity is not important, just focus on the amount.

A multimeter in MIN-MAX mode may not be fast enough to catch the max amount. I used a digital storage oscilloscope in roll mode with 1ms time base. It showed the ramp-up of the voltage beautifully. However, this is not required, because if the protection circuit fires, there are only two possible cases, which a quick multimeter can detect in MIN-MAX mode:

If the voltage is missing, the recovery L section is not working. Most likely, Q451 has a problem as described above. Mine never had a full short. If it has, also replace Q552 and IC522.

If the amount is too high, the recovery H section is not working. Strangely, Q441 does not die, but its companions Q531 and IC502. This is a total mystery to me.

Spare parts

The driver IC I got from  HERE and the transistors from HERE. So far, they seem legit and work ok.

In THIS BLOG POST I talk about possible replacement for discontinued parts. I am trying my luck with the FGD4536 for all the power transistors, including the DG302.

2017-03-31

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 can be booted in a diagnostic mode where it will display 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.



2017-03-27

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 am spending some time to find alternatives.

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 with no long-term experience.

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

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.

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. As of April 2017, DigiKey had still more than a thousand on stock. I for sure have ordered a sack full of them for the years to come, calculating that each scan board eats six of them. My next guess would be the IRG7RA13U. Also difficult to get from trusted sources.

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.

I think the DG could replace all the IGBTs. I'll try that in my next 7 blink patient.

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 DG301 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.

Things are looking good


To summarize: with the RF1501, the STTH20/30, the FGD4536, and the DG302, fixing our beloved Panasonics will be no problem in the near future.

2017-03-01

Onkyo A8470 - speaker relais not clicking - "servo operation" lamp not coming on - degraded glue on protection IC's pins

That was an interesting repair. A friend brought me his Onkyo amplifier. It did not switch the speaker relais on and the servo operation lamp did not come on. Both are controlled by the integrated protection chip Toshiba TA7317 and after some tests and measurements, it became pretty clear that the error had to be there. The amp produced a signal just up to the relais and there was no DC on the output, either.

I remembered a YouTube video where a guy said that in old devices a certain type of glue would degrade and become ever so slightly conductive. Just enough to cause sensitive circuits to malfunction. And what have we got here? A big splash of that brownish gunk right over the pins of the protection IC! They had glued the patch wire to the board with it and splashed glue all over the place.



I cleaned it with acetone and the amp came back to life. I resoldered everything just to be safe that it wasn't a dodgy solder joint.



As a precaution I also took care of the other glue spots: