Hitachi LED TV won't turn on

[JJ_76]

This is my first post since I could not find answers while googling for myself. If there is already an answer out there please point me to it.

Standby light is On.
Did a little research and hoped it would have been some visible busted capacitors.
Didn't see any popped caps although I know they're not always visible.
oOnly thing that I noticed were the burns on the attached pic of the power board.


1. What are the burned components? (T9102/1)
2. If replaceable, what could have caused them to burn?
3. Does anyone have schematics or point me to where I can get them?
4. I found another board on ebay but if I want to replace the components would it be more cost effective?
5. If I replace the board, is it likely it will happen again if I haven't found the cause?

Hitachi LE46S605

power board
715g4565-p02-w20-003h
serial
(T) A2419XZ8
1927661A0005

 

[(*steve*)]

Not sure what burn marks you're referring to.

 

[JJ_76]

picture 5 of 5

 

[(*steve*)]

Hmmm, not the sort of component that I would expect magic smoke to be released from...

 

[JJ_76]

Attaching a couple more pics.

Attaching a couple more pics.

 

[JJ_76]

So I talked to a couple of electrical engineers friends of mine who told me that it is likely that it was a capacitor that cause these transformers to overheat.
Is it possible that these transformers still work and I just need to find the bad capacitor?

 

[davenn]

I don't really see any specific signs of burning
I see lots of solder flux around the terminations

IF those transformers were overheating you would see discolouring of the yellow tape that covers the coils ( pic 1 and pic 5) no discolouring is visible

I suggest that your fault is probably elsewhere

Dave

 

[Claas]

Check the inverter board. Also do you have an in circuit capacitor tester, inspecting visually for bad caps isn't the most effective method. Is the power supply putting out anything? Also could be a bad backlight?

 

[JJ_76]

I had assumed the power board was the problem because of the melted flux on the transformers. It may not be flux at all, I'm thinking the wires got hot enough to melt/burn the plastic surrounding them. I am going to ck the power outputs to see if that is the problem. If I'm not getting the right outputs then I will check the inverter board. I don't have a cap inline tester, all I have is a mulitimeter (fluke 77 and 87). From what I read I have to remove them to check. One on my engineer friends wants to play with it and I'll pass along this info and report back.
As far as the backlight, does it make a difference that it's an LED? I'll keep that in mind if all other stuff checks fine.
Thanks for the help and suggestions. This is my first attempt at fixing electronics. My background is in electrical so this is a bit of a stretch for me but I love fixing stuff and with help I can at least try.

 

[davenn]

I had assumed the power board was the problem because of the melted flux on the transformers. It may not be flux at all, I'm thinking the wires got hot enough to melt/burn the plastic surrounding them

that's still a bad assumption ... the flux is naturally going to look like that after the soldering process. if those termination wires got hot enough to melt the plastic around them, I stand by my previous comment ... the yellow coil covering would be discoloured because of the heat in the coils.
You are looking at a normal manufacturing process, I still say your fault is likely to be elsewhere

Dave

 

[JJ_76]

update

So I decided to test the PSU to see if it was outputting voltages to the other boards.
I've attached pictures to help illustrate.

1. I read approximately 60 VAC on the red side.
2. I get no reading (DC or AC) on the other side of the transformers.
3. While reading across the single smaller transformer the lead touched 2 points and ended up blowing IC 9301 circled in red.
4. After blowing IC 9301 I can still read approximately 60 VAC on the red side.
5. IC 9301 had not markings on it that I could tell from other pictures before blowing.

Questions:
1. What would cause no voltage on the DC side of all transformers? Where would you recommend I ground to read the DC side? I've used the grounds at the screws and the output harness grounds.
2. Does not reading on the DC side indicate the transformers are not converting to DC?
If so, all three transformers?
2. Now that IC 9301 has blown, is it worth replacing or just get another board?
3. Any recommendations/thoughts?

 

[(*steve*)]

I would be very carefully looking to see if I can find the chip of epoxy that flew off the package in your last image. It may have the part number on it.

Failing that, try to find somebody who has the same board and get them to look at theirs for you.

I suspect that is the controller for the regulator (the 7 pin package is not uncommon).

Another option is to trace the circuit around it, then look up a series of similar chips, and find which one(s) use that circuit.

A service manual would be even better as it would possibly list what the device is.

 

[JJ_76]

found the chip

I didn't expect to find this and from the other pictures no writing was visible. It looks more like a stamp that requires good lighting to see the writing.

A6069H
SK153
19795D

Gonna try and find this online somewhere and see if it's worth buying.
I'm having some difficulty locating one with the exact series of numbers. I have found some with the first set but not the second. Does it have to be exactly the same?
Any recommendations or suggestions on acquiring the correct one or substitute?

I went ahead and purchased a replacement board hoping this is the problem.

I am still very interested in finding the problem.

I'm assuming since I can read ~60 VAC on the red side that the problem lies on the other side of the board that has no reading.

The output voltages on the harnesses read 24/12/5 (assuming DC?)

After watching some transformer testing on youtube it led me to believe a component on the non-reading side is causing a short.

Any suggestions?

 

[KrisBlueNZ]

Looks like a Sanken STR-A6069H

http://www.digikey.com/product-detail/en/STR-A6069H/STR-A6069H-ND/3661844

Ex stock, USD 2.29

Good luck!

 

[(*steve*)]

Any suggestions?

Buy a lottery ticket. I had to suggest you search for it, but finding it is very lucky.

I would probably order a handful of those chips. There is a good chane that when you replace it, the first thing that will happen is that it will immediately blow again.

Although with your current luck, it will just start working!

More seriously, I would suggest you take readings across everything that's on a heatsink. You're looking for shorted diodes and/or mosfets. Initially anything with a zero (or close to zero) resistance in both directions is worth a close look. In this case, close to zero probably means less than 100 ohms

 

[JJ_76]

Update:

Got a working used PSU.
TV turns on now.
I still want to fix the old PSU so I'm going to take some readings on the new PSU to compare with the old one.
It's gonna be a tedious process and I'm not quite in a hurry since I purchased another TV while waiting.

Note:
The flux/burns on the secondary of the twin transformers is also present in the replacement PSU.
I have tried to find schematics/service manual for this board/TV and have not been successful, any recommendations would be appreciated.

Question:
Since transformer failure is gradual, is it possible that whatever caused the original transformer failure to be causing the replacement transformers to overheat/burn flux and eventually fail as well?