Help Needed - Thomson 27LCDB03B not working

[micheldeman]

Hi five Astracat! Together we've cracked it, appreciate the help.

Changing U6301 has resolved the problem, TV now back up and running. Just to confirm for anyone looking to fix the same power supply showing the same symptoms and they should subsequently stumble upon this post. The dc voltage to pin 7 of U6301 should be around 14V dc when working correctly. If you have the skills to lift the pin 7 re-measure the voltage at the PCB sniff point and see if it goes up to 15V which supports the IC failure as I found.

Hi, with interest I have been reading this tread as I also have a faulty power supply board. It also has a faulty U6301, apart from some other components. Where could you get the replacement for U6301? I am living in Coventry and have difficulties getting hold of these components.

I have put the list of components that I need here:
Q6301 -> STW12NK80Z
U6301 -> UC3843A
R6310 1206J10 (smd) smd size 1206, 10 Ohm (1/8 watt min.)
R6311 20K (smd) (1/8 watt min.)
R6327 1K (smd) (1/8 watt min.)
D6304 4146 (smd) (1N4148 Fairchild)
R6312 -> 0,27 Ohm 2 Watt

R6301 -> 68K 2 Watt
Q6302 -> MPSR44 (MPSA44G ON Semiconductors)
D6303 -> 4148 (smd) (1N4148 Fairchild)

Optional:
CY6201 -> 2200P, 250V (YL)
CY6202 -> 2200P, 250V (YL)

If anyone could help me out getting these components together, I would be very grateful, or even if somebody could help me with soldering of these smd components, that would be fantastic.

some pictures of my PSU can be found here:
http://www.mijnalbum.nl/Album=WQDMNCI3

thanks,

Michael

[Acrantophis]

Mike, are you looking to make the repairs or do you want someone to repai rthe board for you, your post is confusing as you ask where to source parts but then go on to ask if someone could help do the de-soldering and soldering. I can tell you where to get the SOIC8 device U6301 from and probably most of the other items, but I don't like seeing people waste money buying items that they don't need to so before we go any further can I ask how you have concluded so many items need to be replaced?

[micheldeman]

Hi Acrantophis,

let me try to tell the story in short. I was living in Sri Lanka and brought the TV earlier from the Netherlands (Bought accross the border from a Germany's Media Markt for 1100Euro). It's a 30LCDB03B, which has the same PSU board as the 27LCDB03B.
At a certain moment, when switching on the satellite receiver, the TV (connected via scart) gave a bang and a flash and was broken. I found that the U6301 was burned, it's used for automatically switching on the TV when it gets an (external) power on signal. Together with a friend from the Netherlands, who is in electronics, he suggested to replace the parts and some surrounding ones to be sure. However, I couldn't get the parts in Sri Lanka so got a replacement PSU from one UK tv parts web site. I replaced the PSU with the new one and there was no need anymore to get the PSU board fixed. Meanwhile, we have moved to the UK and so the TV. After a short while, the TV broke down again, it starts, but shortly it sort of powers down. So in fact, I have 2 defect PSU boards. I think the power boards are a common problem for these thomson TV's. You also don't find the brand in the common UK electronics shops (anymore).
Recently, I could get a same TV (27LCDB03B) from gumtree for just one pound, which is now playing. Has only a slightly problem with the LCD screen, kind of memory/burned in problem.

Then I found your tread and was wondering whether I could get my old TV fixed again as it is a nice piano black 30inch one.

I am not an electronics myself, but have some basic knowledge. I am always kind of challenged to get my equipment fixed again and oftenly go on forums to get the problem solved. I Have done washing machines, the power supply of our microwave, rewinded the tweeters of my hifi speakers, repaired our dishwasher, fixed the ceramic cooker, DVD player, my stereo tuner, do my own car repairs, toys of our kids, have done the water and electrics in our house in Sri Lanka, etc, etc, etc. Just as a few examples to mention the type of person that I am in that regards.

So the TV is now under our bed, waiting to get alive again. I am reluctant to just throw it away without trying to fix it first myself. I could do the soldering, but the U6301 might be a a bit too challenging. However, I can give it a try. I also could send you both PSU's if you like, but for the second one, I haven't investigated the reason. It could be just the capacitors as mentioned often as reason for power failures.

thanks,

Michael.

[Acrantophis]

Mike, here is how I would suggest removing the damaged I.C. but remember not to over heat the solder to much as you may end up damaging the tracks of the PCB.

You will need:-
UC3843A - Obtainable here:- http://uk.farnell.com/unitrode/uc3843ad8/pwm-controller-smd-3843-soic8/dp/1101425
or
http://uk.rs-online.com/web/p/current-mode-pwm-controller/6899954/
Soldering Iron with a fine tip
Solder
Possibly a solder sucker or some desoldering wick
A scalpel blade N#11 or other suitably sized blade that can be inserted under the device.
A fine tipped pair of tweazers to position & hold the new device in place whilst soldering.

What to do:-
Firstly - note the orientation of the device. Pin 1 is identified by either a notch at one end of the device or a spot. This should be at the top of the device and pin 1 will always be the top left pin.
Solder all of the legs of the device along one side so that they are all shorted together. Remove heat.
Take scalpel blade - re-apply heat to solder so that it becomes molten and then ease blade under device. Whilst solder is still molten ease device up away from board on this side. Repeat the above for the other side, once the device is lifted away from the board on either side you can then re-heat solder both sides of the device and hopefully remove the compenent from the board.
Clean up any excess solder from the pads with the aid of the de-solder wick or solder sucker, try not to lift the pads by excessive exposure to heat though.
Take the new device with the tweazers and position it so that  the legs line up with the pads and the device is in the correct orientation as mentioned at the beginning regarding the removal of the faulty device. Solder the new one in place being sure not to short any of the pins together, (if you do use the de-soldering wick or solder sucker to remove excess if you can not remove it with the soldering iron itself).

Regarding the other board I would certainly suggest replacing the electrolytic capacitors they only cost pennies so its hardly going to break the bank. If you need me to see if I can identify part numbers for you from RS or Farnell just shout and I will see what I can do.

[micheldeman]

hi Acrantophis,

thanks for your extensive explanation. I have been on the web site of farnell and placed most of the parts, except the smd resistors (was thinking to use conventional ones), in my shopping basket. In some cases I needed to order a minimum of 5 or 10 pieces of a component. That's fine but I am with about 12GBP still under the minimum order amount of 20GBP.

Therefore I was thinking first to try to replace the capacitors on my other board. That will cost indeed just a pound or so. If that would solve the problem with that board, I am there already. I can then still decide later on to try to repair the first board or not.

[Acrantophis]

Mike, if you can get the parts through RS then you could collect from their trade counter in Birmingham, assuming it is not to far for you to travel.
Duddeston Mill Road,
Duddeston Mill Industrial Estate,
Birmingham,
B8 1AP

Alternatively the U6301 device can be sourced through Ebay http://www.ebay.co.uk/itm/UC3843BD1G-UC3843B-PWM-Controller-Current-Mode-52kHz-SOIC8-/300617498920?pt=UK_BOI_Electrical_Components_Supplies_ET&hash=item45fe330128

I looked at the Maplins website when I was searchign for them but couldn't find them, however they may be able to help you for the other parts and the surface mount resistors.

I'll keep checking the post daily so if you need any help just ask.

[micheldeman]

hi Acrantophis,

ebay, never thought about that, how genius.
I am going today to maples for the capacitors and will see what the result of that for the second board is.
Then subsequently going for the other parts, ordered already two (one spare) of these U6301 devices through the ebay link.

will keep you updated.

thanks,

Michel

[micheldeman]

Today I went to Maplin (not maples, I always confuse the two names) to buy the capacitors, but they had not much of them in stock, so I went to RS components in Nuneaton. I have bought all of the capacitors, except the C6311 of 150uF which was not in their catalogue. According to the service manual, the value should be 100uF, so I got the 100uF ones instead. Same like the value of C6314.

What do you think, is it wise to just use the 100uF or still go for the 150uF one? There must be a reason that they have used 150uF in production, rather than the 100uF as designed?

I also tried to get some of the other components from my list in order to repair the first board. So far, I only got the transistor Q6302 MPSA44G, they didn't have the Q6301 STW12NK80Z, so I left that for later. The U6301 should come trough ebay. Then I still need to get hold of the smd diodes, which was a bit difficult for me to order as I don't know about sizes etc. They also come in large(r) package sizes or on roll. Resistors I should be able to get through Maplin as I was thinking to use conventional ones.

thanks,

Michael.

[micheldeman]

I have replaced the capacitors, for the 150uF I have put 100uF and 47uF in parallel.
It looks like the TV is a bit more stable, at least a picture comes up, but still after a few seconds it switches off again. Led remains green and I can turn off the TV by remote as well.

I expect the U6301 to arrive shortly, so I will just try to replace it and see what happens then.
I haven't swapped and tried the PSU from the other good working TV yet, just to exclude that the failure may come from another part inside the TV. Will be another step when replacing the U6301 gives no good result either.

to be continued...

[Acrantophis]

Mike, what is the baord number? The board I repaired had capacitor values as per the schematics/circuit diagram. As manufacturers can change components from time to time I'm wondering if you have a different board rev level.
For the diodes marked 4148, like D6303 (located between the emmiter of Q6302 and pin 7 of U6301) try LL4148. Effectively a standard 1N4148 diode but in a surface mount package. Again ebay is your friend for these :- http://www.ebay.co.uk/itm/LL4148-SMD-minimelf-Diode-Pack-100pcs-/290605876056?pt=UK_BOI_Electrical_Components_Supplies_ET&hash=item43a975c358
I would only use Maplins (Maples) out of desperation and wanting to be further dissapointed as they are 1 step short of being useless and also over priced for parts.

Good luck

[micheldeman]

Boardnumbers may differ in versions. They are currently built in, so can't check the numbers.
I didn't receive the U6301's yet, so meanwhile I have exchanged some boards from the good working TV into the faulty TV and vice versa.
It looks like the powerboard of my faulty TV is fine as my good working TV has no problems with it. When I put the power board of my good TV into my faulty TV, I still have the same problem.

So I started to exchange the connector board. still same problem with my faulty TV
I exchanged the main board from the good working Tv into the fault TV, still same problem.

However, I had some situation where the faulty TV worked for some minutes or so and then shuts off. Power led still giving green. Remote controll not working except for the switch off button, greed led turns green. I can restart the TV afterwards by pushing the power button again.

What actually happends is the following.

The faulty TV turns on normally, picture and sound come on.
Then after some time (between 30secs and 2 minutes) the screen disappears, like it blows up, some red colour is visible and after that you only see some grey light on the back ground. I don't know if this is the back light still functioning or not. Also the audio disappears at the same time.

What I am thinking is that the power supply is overloaded at some point where it shuts down or something. Or the main board detects some fault and shuts down. No idea to be honest.

I just replaced the audioboard to test. Same problem.

I think I will try to replace the invertor board. May it overloads the powerboard somehow so that it fails to supply the power.

[micheldeman]

I heave been testing a bit more arround and start to think that the power supply is underdimensioned for this 30inch TV. When the TV is brand new, the powersupply will stand the consumption, but when it gets older maybe not. However, I must say, when I used the connection board and main board from the good functioning TV in my faulty one, it took a bit more time before the TV shutted off, but still it was not functioning properly.

What else to try? I will check the board numbers and components of the different PSU's. May be there is a difference between the 27 and 30 inch version.

PS: I swapped the PSU permanently, so my good functioning Tv is now playing on the PSU of my faulty TV just for endurance testing purposes without any problem.

[Acrantophis]

The problem could be that the circuit diagram I attached does not match your board and so could misleading, it would also explain why you have a different capacitor value to that shown. Having looked at the block diagrams for the 27 and the 30 inch TV's I would say that there are certainly difference between the two sets, the 27 has the audio, DC+DC, and PFC circuits all on the one board, where as the 30 has a seperate audio board. The connectors/wiring looms will also be different.
Perhaps opening a different post may be the way forward as there may be someone who might know more then me.

[micheldeman]

Short reply to what you write,

in both Tv's, the audio is separated from the PSU board, unless your's is integrated, then there are differences. I must say, there are some differences between the boards, but they look compatible. Nevertheless, I will see what else I can try, first I will check whether there really no differences between the power boards.

Thanks,

Michel

[micheldeman]

Hi Acrantophis,

Today I received ( a bit late) 2 pieces of a the 3843B ic's.
However, I can't identify pin number 1. The IC doesn't have a spot or something similar. It only has, apart from the number indication, a white line at one of the top sides. Would that indicate the top of the IC. I think it must, otherwise there is no other indication how to find pin number 1?

I have found that my TV plays when the source (e.g. a DVD player) is put on pause, so accepting still images. As soon as I resume the DVD, the TV shuts off. It looks like when the TV has to handle moving pictures, it shuts off, but still images, or when the DVD starts it's screensaver, it keeps functioning. I also can play for instance a music CD. Also then the TV keeps playing, it's only when playing moving pictures from DVD or other sources.

Looks like the PSU is incapable to supplying enough power???

What do you think?

I am trying to repair my original PSU. However, however removing the U6301 was already a difficult thing, as one of the pads is lifted. I will try to place the new u6301 very carefully.
thanks,

Michel