I need professional help!

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Old 04-20-09, 12:09 PM
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I need professional help!

Any tv techs checking this? Please help me cut through the professional jargon and tell me what is the mainboard in a sony bravia LCD.

Is it the AU board - the one with all the inputs?

And would a failed main/AU board manifest itself by causing a normal audio, no video, (with a low backlight) condition?

As guidance, the unit in question is a Sony KDL-40S2000.
 
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Old 04-20-09, 03:38 PM
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Yes, typically it is the pc board all the cables attach too, like your RCA cables, etc.

Hang in there and one of our other guru's can respond to whether or not that's your problem.
 
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Old 04-20-09, 09:59 PM
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Thanks Mark. I'm standing by.

Background: The set is a gimmie from my brother who was going to put it in the landfill. Failed within a week after warrantee expired. DOM is March of 2006 and it sat in a closet since last summer when it failed.

Thought I'd give it a try and look for something obvious - loose connector, broken wire, etc. The thing cost him like $2500.

Ended up disassembling the entire unit, pretty much. It was a snap. Unfortunately I did not see (or smell) anything abnormal.

Anyway, I'm looking at a total of 6 boards. Checking around, it appears that I could shotgun the whole thing (with salvaged parts) for under $300.

But I got couple of numbers from Sony for authorized repair places. And, while speaking with one of these techs he mentioned that he sees this frequently - and he would bet a months salary that it is the "mainboard".

Does my question make more sense now? Sony does not refer to any of their boards as the "mainboard". I am fairly certain it is the AU board, but thought I would seek help here.

Again, thanks for the response.

Jerry
 
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Old 04-21-09, 06:43 AM
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Here is a list of boards: Line Brand Chassis Description Model OEM Status
SONY AU KDL-40S2000 A1192415-D Sony BU (BOARD MIGHT HAVE "B") KDL-40S2000 A1179493A SNA
SONY H3U KDL-40S2000 A1172591D SNA
SONY H1U KDL-40S2000 A1172589D SNA
Sony G2 KDL-40S2000 A1169591E SNA
SONY QT (Replacement for A1164341A) KDL-40S2000 A1164341B AVA

Sony QS KDL-40S2000 A1153812B AVA
SONY QS KDL-40S2000 A1153812A SNA SONY H2U KDL-40S2000 A1152234E SNA
SONY LCD PANEL KDL-40S2000 18020591
The AU board would be my first guess.But it could easily be just a blown fuse.Since you already have it a
part,check all the " Pico " fuses to see if any are blown.They are on every board.
 
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Old 04-21-09, 11:49 AM
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tks craftsman 50,

I will check the pico's (after I find out what they look like). Just a continuity check with a Fluke? Can they be checked while still in the circuit board or must they be pulled?

But regardless, the failure, as described to me was kind of gradual over a period of a week or so. Usually not indicative of a blown fuse (I think).

Thanks and regards,

Jerry

Oh boy! Disregard my previous. I have some serious research to do. Picos can fail in degrees? A quick google search only shows commercial sites - not one site explains their construction or function. And after several minutes of staring at my boards I can't see anything like the images of the fuses for sale.
 
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Old 04-21-09, 05:15 PM
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That sound like a good possibility it could be a bad cap on the power supply board.The pico fuses can be checked in circuit.Do a serch on them and you'll find a pic of what they look like.
 
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Old 04-21-09, 06:26 PM
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Pico Fuse:

 
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Old 04-21-09, 06:37 PM
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Pico fuses often look like small resistors, but frequently are labeled on the board with a fuse symbol. In the circuit they will measure less than an ohm when good. Anything above that is circuit dependant but usually indicates an open fuse.

Hard to test caps with a digital meter, at least my way, but look for the plastic covering to have shrunk away from the top and headed down the sides. An indication of heat.

Do a visual check of the solder side of the board looking for bad solder connections, especially any heat related components. You will sometimes see indications of heat on the board as an indication.

As you suspected, a fuse is usually a rapid failure, but a cap is often a slow failure.

GL
Bud
 
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Old 04-22-09, 01:53 AM
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Thanks Bud. Thanks Mark.

Attached is an image of my boards. I have scrutinized them for over 2 hours. Every component on them that looks like a resistor is exactly that - a resistor (or in a couple of cases, a capacitor).


I have learned, since this afternoon, that pico fuses are so-called because they are rated in pico amperes. That 's trillionths of an amp - correct?

Is the schematic symbol for a pico fuse tha same as for a standard buss type fuse (the ones that snap into a fuse holder)? I've only ever seen the normal long flat sine wave symbol as used on products built for the US market.

Forget the image - I can't find the attachment button and I am too tired to figure out where it is right now.

I will try again later on, after I sleep for a few hours.
 
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Old 04-22-09, 05:50 AM
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Photobucket.com seems to work. Then post the link over here.

The sine wave symbol is what I would be looking for. Not sure where they got the pico name. as I have them in sizes up to 3 amps. I've always assumes "tiny" as they are smaller than the glass fuses.

When looking for cold solder connections, I use the tip of one finger on the solder side of the board and wiggle the component gently. It's amazing how sensitive the hands are. The bad connection forms after the board is put in service due to constant heating and cooling of the lead/solder interface. Eventually a fracture forms around the lead making a poor connection. I read a service bullitin from IBM years age where they estimated that 75% of their board returns were due to cold connections that formed in the field. It is more often associated with older boards, so yours is a lower probability, but always worth checking.

Have you tried searching for "board level repair (for your tv)"

Bud
 
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Old 04-23-09, 05:51 AM
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As an example, I am providing an image of my power supply board - could one of you gentlemen please identify the location of one pico fuse.

Thanks
 

Last edited by chengny; 04-23-09 at 05:58 AM. Reason: spelling
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Old 04-23-09, 06:09 AM
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Ok, this board is using fuseable resisters instead of pico fuses.The best way to troubleshoot this would be to put it back together and check for missing voltages at the connectors.I notice they are all marked with whats on each pin.
 
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Old 04-23-09, 06:37 AM
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No picos on the PS board. One ceramic fuse bottom left corner (white). The two blue caps right side show some sign of plastic cover pulling back, a possible indication of heat. The picos will look like the photo Hotin posted and are about 3/8 inch long.

On the group photo, the bottom long board has three components just to the right of the ribbon connector in the center, yellow and vertical, that is what one would look like. But can't see for sure what those are.

Trouble shooting by sight or ohm meter is at best guessing, unless you get lucky, but takes years of practice. I use an analog meter primarily because I have always used one. Digitals drive me crazy.

Not much help, but tried,
Bud
 
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Old 04-23-09, 07:27 AM
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Geez Bud, you've got a wicked good eagle eye. That backlight inverter board was the only one I wasn't looking at. It just kind of got separated from the rest.

Sure enough, those three orange? (I'm color blind) resistor-like components that you mentioned must be pico fuses. Labeled as F001, F002 & F003. Unfortunately they all checked out as good.

But I'm telling you those are it for picos - as far as I can see. I talked to my bonehead of a brother last night. He now tells me that the set acted up (video went on and off) for over two months before it finally kicked the bucket for good.

I am going to move away from the pico fuse theory for now and start looking at caps on the PS board. That is the most expensive to replace ($139) and I would spend that in a hearbeat if I only knew for sure that it was the definite problem.
 
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Old 04-23-09, 04:51 PM
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Well that definately sounds like a power supply problem.You can always order one from a place that will let you return it if it does not fix the set,normaly a 20% restocking charge.
 
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Old 04-23-09, 09:33 PM
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Really? Thanks for the heads up. Any site like that come to mind? Does ShopJimmy do that?

I just want to say thank you - thanks to all of you for your assistance as I muddle through this thing. If I sometimes seem distracted - I am doing the final work on my garage (heating/duct work & electrical) and wrapping up a restoration of my 86 GMC Sierra Classic K2500. This TV is like the last thing on my priority list, but my kids are begging for a LCD HD TV so they can be like all their friends.

If it were only me, I'd watch a B&W portable and be happy - except when the Pats are on.

Oh and Bud, I checked the board level repair angle... nothing really. But at least now I know what it means.
 
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