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Test Equipment Anonymous (TEA) group therapy thread

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tggzzz:

--- Quote from: Cerebus on July 05, 2022, 07:13:20 pm ---Roger Needham used to recommend that your passwords should be "shocking nonsense", the shocking bit intended to make you think twice before telling someone your password. On that basis perhaps one should use one's 11th digit, the middle wicket so to speak, so that you aren't tempted to reveal your *ahem* original biometric in public. Of course revocation would be particularly undesirable.

--- End quote ---

I can think of people for whom it would benefit mankind. Much like retrospective abortion.

tggzzz:

--- Quote from: mansaxel on July 05, 2022, 07:53:24 pm ---
--- Quote from: tggzzz on July 05, 2022, 05:12:52 pm ---The rest, not so much: a major benefit of going out is to inhabit somewhere completely different, not to stay in cyberspace.

--- End quote ---

The trick is to do Augmented Reality -- experience the Real World enhanced with information from Other Places. It makes the Real World a more multifaceted place. And it takes less time to immerse yourself into something when you can apply the aggregate previous knowledge of the world on top of the actual experience.  The most obvious example to me is GPS and electronic maps.

--- End quote ---

That feels close to someone else indicating what I should experience, and to avoiding thinking and planning, and accidentally avoiding serendipity. (One of my favourite concepts and words!)

Do offline research, then experience X for yourself, then do research to find what you missed. And equally, what other people missed.

Vince:
TV REPAIR

OK, here goes.

Simply removing the back cover was an adventure in itself. It's not designed to be removed. No. Not a single screw. Instead a shit load of very, very stiff plastic clips that bite into the metal chassis, real hard. Two rows of clips. One that's 2 inches from the edge, another that's 4 inches from the edge. Only way about it, is to pry the cover off by shoving a long beefy screw driver deep under the cover, and pry, hoping the cover, which flexes several inches in the  process, won't explode. Luckily for me the plastic held up, no drama, but boy that was close. I was really, really scared....  :scared:

The two big black boxes at the bottom that look like VHS tapes... aren't VHS tapes (I checked). They are the speakers, of course  ;D

OK so straight to the LED connector to see if I can swap the strings there.... problem again : there are no wires going to the power board... nope. Look how they made it... there is a connector that's attached to the chassis, and the power board plugs straight into that connector, no wires ! So I can't swap the strings to trouble shoot things !  :palm:

Oh I am only 15 minutes into this thing and I already want to scrap if for parts. But I can't... not this one.
Plus I checked date codes on the board and this freaking thing is only 3.5 years old ?!  :wtf:
The other TV I worked on was 15yo, so I didn't care too much about it... but this one is a 55" Smart TV 4K that's only 3+ years old ?!
So it's probably still worth a little something and the owner might indeed be happy if I can fix it... then he will owe me with his  bucket truck !!!  >:D

OK, so I can't swap the strings, pfff.... what next.

The connector is 12 way, and only the first 8 pins are used / populated.

So looked at the power board, big TH components, traces around the connector....

There is a pinout table printed next to the connector, on the silk screen, how nice. It confirms that only the first 8 pins are used.
The 8 pins are labeled as follows :

1+
1-
2+
2-
3+
3-
4+
4-

So that would mean 4 independent strings.. potentially, but it means squat because I can't access the LED strips to see how they are wired. I can't remove that connector from the chassis, or I would cause damage...

However what I can do is buzz the pins to see if all the anodes and cathodes are independent or not. They appear to be, no two cathodes or anodes are tied together.
OK that's good. I mean if there are 4 strings in this backlight, and half of the backlight is dead, that means that two adjacent strings failed at the very same time.... unlikely.

It's now more likely that the power board is bad.... even more likely because of this : looking at the tracks at the connector, one can see that the anodes of string 1 and 2 are tied together, as well as their cathodes. Same for strings 3 and 4, their anodes and cathodes are connected together.

Looking at the board layout at the top side, you can see we have two "channels" (even labeled as such on the silk screen, conveniently).

So... it's looking good isn't it ? Now it's more likely that the fault is on the power board, no need to take the fragile LCD sandwich apart to get to the LED strips (at least for now...), what a relief !!!!!  :phew:

As you can see on the relevant pic, each channel is made of :

- one diode
- one power resistor
- one small blue disc ceramic cap
- one film cap
- next to one big ass coil
- and of course the pièce de résistance, one big TO220 trannystor !  8)  A 5N50, sounds like a MOSFET kind of part number doesn't it.

OK so I am done for tonight, but tomorrow I can then start working on that board.

First power it up to figure out which channel works and which one doesn't.
Then try to see within that channel, what component is dead... assuming I am lucky and it's one of those few big TH components, rather than one in a million tiny SMD components on the under side of the board.... with no schematic and board layout to help, I have zero chance of fixing this board....

So let's check the easy stuff first and cross fingers that we get lucky !  8)

I guess of course the most likely suspect is the MOSFET. So I could just remove it, should be easy, and stick it in my superb, very helpful 5 Euros Chinese component tester... I am so happy I bought this horrible thing, one of the best investments in the lab  8)

Stay tuned !!!    :-DD


Cerebus:

--- Quote from: tggzzz on July 05, 2022, 10:08:49 pm ---
--- Quote from: Cerebus on July 05, 2022, 07:13:20 pm ---Roger Needham used to recommend that your passwords should be "shocking nonsense", the shocking bit intended to make you think twice before telling someone your password. On that basis perhaps one should use one's 11th digit, the middle wicket so to speak, so that you aren't tempted to reveal your *ahem* original biometric in public. Of course revocation would be particularly undesirable.

--- End quote ---

I can think of people for whom it would benefit mankind. Much like retrospective abortion.

--- End quote ---

I believe the term of art is "Elective post-partum termination".  >:D

BU508A:

--- Quote from: Vince on July 05, 2022, 10:31:12 pm ---First power it up to figure out which channel works and which one doesn't.
Then try to see within that channel, what component is dead... assuming I am lucky and it's one of those few big TH components, rather than one in a million tiny SMD components on the under side of the board.... with no schematic and board layout to help, I have zero chance of fixing this board....

--- End quote ---

I recommend to look out for the datasheet of the controller IC. The manufacturer are following often very closely the design recommendations given in the datasheets. Helped me in the past several times.

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