Saturday, April 12, 2014

Hisense 50K360G dead with blown main board SAG7.820.5028/ROH

A week ago a customer brought in a Hisense 50K360G LED TV with the complaint of being totally dead.

At first we thought it would be the power supply, but a quick check on it showed this was not the case.

Before the pictures a few quick notes on the brand, times, politics and other important author observations almost certain not to be closely related to the issue at hand.

When I was in China last year (how many TV repair technicians can say that, eh?) my local guide was Cindy, the sales girl for our vendor partner there. Actually at the time she has already left them and they were a bit annoyed that it was exactly her who was my guide. I choose her because she offered it, I did need a guide (and you would likely need one too!) and finally I did not actually know well their new sales person, which is by rule the only person (or people) in a Chinese company that speak English. Now I know Ana better and I would not mind her being my guide next time around, of course if only she offers it.

Not really sure if both offer to guide me, but rest assured if it ever happens I'd blog about it, under a pseudonym if I must :-)

So Cindy told me that in China Hisense is a popular brand that is considered quality.
I guess kind of like MacDonald in US :-)

Looking at board design and construction I could also tell that either Hisense has been either making boards or licensing TVs to some American brands for some years or , at least, has been using the same sub-contractors to do boards for them as well known American brands.

Which kind of puts them at the same high level.

Which is all to say that I do like that I've seen from the brand. And I also liked the slim and elegant - if not ground breaking - design of the 50K360G.

Only it was dead as a brick.

Here's what we found inside:

Dang it, this is the reason why it is so cheap: there's practically nothing in there!
A good 'ole plasma TV would hardly leave enough room for dust and when you open it you'd have the good feeling that there must be millions of things that could go wrong , they all have to be checked and customer would simply have to pay for all of it...because it was big, stuffed and expensive..and not just big, empty and cheap!

Anyhow, we measured the voltages on the power supply board and they were somewhat OK.

I say "somewhat" because they aren't exactly typical for a TV. A typical TV power supply would have a standby voltage of about +5V, a power board signalling pin that wakes up the rest of the output voltages and lots of connectors and pins on them where you can measure those voltages.

On this TV there was no +5V standby, but there was a power-on pin and that is even more confusing because on standard televisions the power-on pin usually takes +2.5V to +5V (logical 1) to wake up.

On this power supply board one didn't even have +5V handy and passing what was available was against, hmm, commons sense and past experience.

What is available is 12V and 15V if memory serves me well.

Luckily the power supply board specifications are printed on the board itself - BTW another sign for a higher end manufacturer.

TO cut the story again, the power supply board indeed does provide +12V in standby mode and indeed takes +5V to activate the rest (which isn't much).

Also, just like most other LEDs, the power supply produces AC voltage for empowering a chain of LEDs as opposed to DC voltage you'd expect if you just think of LEDs.

Here's a close-up of the main board SAG7.820.5028/ROH (click to enlarge):


And here's a close-up of the top of the board that drew our interest:
 
As you can see this is a fairly well smoked component.
This is the voltage stabilizer that takes the +12V standby voltage and makes +5V out of it.

The same +5V you can use to manually engage the power supply BTW.

Here's our advice: do not try to replace it. The same thing is likely going to happen.

Modify the board to incorporate a more powerful stabilizer or send it to us and we'd do the modification.

We were able to repair the board all right, but there is no guarantee this will always be possible.

After all, when that thing fails, it may short the +12V input to the +5V output, sending the next circuits 140% power increase...and some of them may quit.

None of ours has done it, luckily, but this is what we found when we started the TV again:


Either the customer or we have broken the LCD display and now the TV has the value of my old running shoes, even without the odor!

You know what we did?

We paid the customer $150 for that TV because we weren't certain if it was us or her and we figured we can keep it and do repairs on the main board and the power supply board for people like you.

And I am not making this up.

I must say this is the first time something like that has happened. We've bought broken TVs before, of course, but frankly $150 is fairly high for a TV that will never sell.

Meaning we won't be doing it every time someone brings in a broken large screen TV :-)

1 comments:

Dean said...

My voltage "out" on the power supply on my Hisense 50k3606g is 16.47volts on the 14 volt pins and 12.9 volts on the 12 volt pins. The set turns on and the standby led blinks 7 times pauses then blinks 3 times. after that the backlights will flash on for 2 seconds then shut off 4 seconds then keep repeating the on/off cycle.When the backlights flash on I can see the menu screen momentarily. This must have a auto reset surge protector of some sort. The set does the same thing with the LED driver board disconnected. There is no evidence of burned/bulging components on any of the boards that I can see. Am I right to assume that the Main board is what triggers the backlights to come on and stay on ? The reps at Hisense are useless and actually quite rude after I gave them the model number of the set. After them tap dancing around and denying there is a problem with their products, I reminded them of all the sets with the same problems over 50 blogs (at least 20 per blog) I went on. Seems to be a lot of problems with these. You seem to be one of the only techs that expresses opinions other than take it to a repair shop. The local shops have told me to junk it, not worth fixing...If there is some way you can help me out, it would be greatly appreciated. Thank you for your courtesies, Dean

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