Sanyo DP46849 46" LCD - Does not power up.

[Deebeaux]

I feel that I'm pretty handy at fixing electronics, but I haven't really worked on a TV in quite some time. Boss brought three TVs from his house that quit working at one time or another. One was a blown fuse, I'm on the second one and am experience these issues.

It's a Sanyo DP46849 and it does not power up at all. There's no pilot light lit on the front (I'm assuming there's supposed to be) and I am fairly certain I do not have the 5V Standby that I've read about here (thanks to Bud Martin for his guide). Looking for some advice as to where to look.

Attached are the best photos I can come up with here at the office (iPhone 5) so I took one top-down of the power supply board and two of the connector areas so the labeling can be clearly read.

I was at a slightly angle when I took the picture, so the main AC fuse is obscured in the photo, but I checked it for continuity and got tone, as well as confirmed 120VAC on both sides of it. I checked for DCV between the GND and STB5V pins on the connector and got nothing. Short of "shot-gunning" it and checking every diode/etc... looking for advice as to where to look first. None of the capacitors have obvious damage (to me at least) and there's no obvious burns or discolorations on the board that I can tell.

Thanks for any advice offered. If the pictures aren't of suitable quality I'm happy to take them with my DSLR and post them.

Dave

[retiredcaps]

Re: Sanyo DP46849 46" LCD - Does not power up.

There's no pilot light lit on the front (I'm assuming there's supposed to be) and I am fairly certain I do not have the 5V Standby that I've read about here (thanks to Bud Martin for his guide).

Thanks for doing some homework first before posting.

Attached are the best photos I can come up with here at the office (iPhone 5) so I took one top-down of the power supply board and two of the connector areas so the labeling can be clearly read.

They are excellent for our purposes.

On your board are two large filter capacitors (KMG 400V 150uF).

What is the DC voltage across the legs of each one? WARNING. It could be as high as 400V DC so be careful. If you have aligator clips on your multimeter probes, I suggest using them (like I do).

[Deebeaux]

Re: Sanyo DP46849 46" LCD - Does not power up.

Thanks for your quick response! Thanks for the warning...I love my trusty alligator clips for my probes. Keeps me that much further away from my healthy respect for electricity.

Both of the KMG 400V/150uF filter capacitors show 163.7-ish VDC.

All readings taken with a Fluke 189 (just for reference).

Dave

[tom66]

Re: Sanyo DP46849 46" LCD - Does not power up.

Good voltage. 163V is fine for standby. So, to check. On STB5V, you measure <0.005V, or just a few volts?

[awyatt2]

Re: Sanyo DP46849 46" LCD - Does not power up.

most likley the control board i have a 42 ich version and it is wating for the control board to come in. supposedly tomorrow morning. check it in a dark room and see if the screen has a dim glow. if so u have a bad control board or a panel bad. the cntrl uses bga soldering as in an xbox 360 and is prone to failure. sanyo tech told me this while he was here. says only a few get serviced under factory warranty, others fall outside. mine was 11 months out of walmart.i also had extended 2 yrs warranty.

[Deebeaux]

Re: Sanyo DP46849 46" LCD - Does not power up.

Good voltage. 163V is fine for standby. So, to check. On STB5V, you measure <0.005V, or just a few volts?

0.3955V tested for the STB5V using a chassis ground AND the pin in the same connector as the STB5V.

most likley the control board i have a 42 ich version and it is wating for the control board to come in. supposedly tomorrow morning. check it in a dark room and see if the screen has a dim glow. if so u have a bad control board or a panel bad. the cntrl uses bga soldering as in an xbox 360 and is prone to failure. sanyo tech told me this while he was here. says only a few get serviced under factory warranty, others fall outside. mine was 11 months out of walmart.i also had extended 2 yrs warranty.

No dim glow from panel in a pitch black room.

[budm]

Re: Sanyo DP46849 46" LCD - Does not power up.

This may help. Try heating up those two startup caps with hair dryer to see if the 5vstby will start running, it is an always on power supply.

[Deebeaux]

Re: Sanyo DP46849 46" LCD - Does not power up.

Oh, wow, thanks for that handy diagram!

I did the hair dryer bit, but it doesn't seem to bring the STB5V back to life. Not exactly sure on how much to heat them up. The hotter I got them the lower the STB5V reading became (Was 0.3995 down to 0.2xxx-ish VDC). Not sure if that tells any stories.

This may help. Try heating up those two startup caps with hair dryer to see if the 5vstby will start running, it is an always on power supply.

[tom66]

Re: Sanyo DP46849 46" LCD - Does not power up.

OK, check this diode.

1. TV off & unplugged.
2. Meter on diode test.
3. Red probe on one end, black on other - record reading.
4. Reverse probes - record reading.
5. If possible note down part number.

[Deebeaux]

Re: Sanyo DP46849 46" LCD - Does not power up.

Results:

Red on Cathode, Black on Anode = .9305VDC
Black on Cathode, Red on Anode = .2205VDC

Part number is a little more difficult to read. Definitely starts with LT7, might be LT77. Under the LT7 it reads SB. If anyone has a schematic it's labeled as D605 on the board.

If it's imperative we get the full part number I can remove it from the board tomorrow.

Thanks!

[tom66]

Re: Sanyo DP46849 46" LCD - Does not power up.

We don't need part # for now it looks OK but just to be sure can you lift one leg of the diode and test it & see if you get a different result.

Then, carefully, on the caps budm highlighted before for heating, please check the voltage across them (positive probe on positive, negative probe on negative.) One will likely be for standby controller.

[budm]

Re: Sanyo DP46849 46" LCD - Does not power up.

What is the little 8-pin IC in the 5STBY section.
Also post good clear pictures of the bottom side as a whole, and also four 1/4 section that are really clear and focused so I can trace the connections.

[retiredcaps]

Re: Sanyo DP46849 46" LCD - Does not power up.

Thanks for the warning...I love my trusty alligator clips for my probes. Keeps me that much further away from my healthy respect for electricity.

Yes, I practice what I preach. Those that don't

“If you hold a cat by the tail you learn things you cannot learn any other way.”
Mark Twain

All readings taken with a Fluke 189 (just for reference).

[Deebeaux]

Re: Sanyo DP46849 46" LCD - Does not power up.

Everyone here is so helpful. Thanks a bunch! I had to call it quits for today, but I'll be back at it tomorrow with some downtime at the office. I'll get those pics up ASAP and when I can pull the board to lift that diode leg I'll give that a shot. Need to bring the soldering station to work tomorrow.

I enjoy being part of the "fix-it" generation instead of the "throw-it-out-and-buy-a-new-one" generation. It's communities like these that make that possible.

[Deebeaux]

Re: Sanyo DP46849 46" LCD - Does not power up.

We don't need part # for now it looks OK but just to be sure can you lift one leg of the diode and test it & see if you get a different result.

Haven't had a chance to do this yet, will try it later this afternoon. Unless the other info I've supplied here renders no need to attempt this.

Then, carefully, on the caps budm highlighted before for heating, please check the voltage across them (positive probe on positive, negative probe on negative.) One will likely be for standby controller.

Referencing the picture budm highlighted for me, the top one is designated as C612 and shows 5.808V, the one below it is designated C634 and is showing 1.28XV. C634 seems to fluctuate a lot and never really hold a reading, seems to be 1.27X-1.29X.

What is the little 8-pin IC in the 5STBY section.
Also post good clear pictures of the bottom side as a whole, and also four 1/4 section that are really clear and focused so I can trace the connections.

THe 8pin IC is labeled with three lines of text as follows:

M846
TNY274PN
58514J (the 1 (one) could be a capital I)

Attached you will find the requested photos.

Yes, I practice what I preach. Those that don't, “If you hold a cat by the tail you learn things you cannot learn any other way.” - Mark Twain

Very good advice and an excellent quote that explains it perfectly!

All readings taken with a Fluke 189 (just for reference).

Haha! I didn't include this for kudos, but more of a "I'm not using a $3 meter and giving 4-5 significant digits." This meter is way overkill for what I do (some electronics, testing power supplies, but mostly building 120VAC/240VAC/208 Y/277 DELTA/etc... My old meter was fried by a "master electrician" years ago and I bought this one. Have never regretted it. You'll cuss and complain about a crappy tool or instrument throughout its life, but you'll never do that for a quality tool. Frankly, I love this meter, we've been through a lot.

With all this information if someone could advise me if it's still worthwhile to life the leg of the diode tom66 mentioned and retest let me know, if so I'll do it this evening. I brought the solder station up to the office just in case.

[budm]

Re: Sanyo DP46849 46" LCD - Does not power up.

OK, that TNY274PN IC is for the standby 5v power supply. Take the resistance reading between the ground pin and the other 7 pins, report the readings.
Next, you will use the Negative leg of the large 400V cap for the ground ref point (It is the ground ref point for the Primary-HOT side) and the use the red probe to check the voltage reading on all 8 pins, the example circuit in the data sheet should be real close to what you have on the board. Since the voltage is fluctuating, it can mean that the start up caps are bad or it is sensing shorted circuits some where. You can test this board by itself without other board hook up to it. You can solder in 47 Ohms 1W resistor to 5vstby pin and ground to give about 100mA load for it.
Report the voltage reading on the IC.

[Deebeaux]

Re: Sanyo DP46849 46" LCD - Does not power up.

Hrm, okay. We're venturing into territory where my electronics becomes a little fuzzy.

Does it matter which 400V capacity I use the negative leg on?

Which pin is the ground pin? There's 1 drain pin and 4 source pins that appear to be connected to the same thing. Would the drain pin be the ground pin?

edit: scratch this below, I didn't even see the sheet you attached! Sorry!
--- I'm comparing it to the attached data sheet from Mouser. (Assuming it's the right sheet.) ---

I'll have to dig through the box or get a hold of an appropriate resistor for load. Do I need to have that soldered on before doing any/all of the above tests, or would performing them with the other board attached provide load?

OK, that TNY274PN IC is for the standby 5v power supply. Take the resistance reading between the ground pin and the other 7 pins, report the readings.
Next, you will use the Negative leg of the large 400V cap for the ground ref point (It is the ground ref point for the Primary-HOT side) and the use the red probe to check the voltage reading on all 8 pins, the example circuit in the data sheet should be real close to what you have on the board. Since the voltage is fluctuating, it can mean that the start up caps are bad or it is sensing shorted circuits some where. You can test this board by itself without other board hook up to it. You can solder in 47 Ohms 1W resistor to 5vstby pin and ground to give about 100mA load for it.
Report the voltage reading on the IC.

[budm]

Re: Sanyo DP46849 46" LCD - Does not power up.

You solder the resistor in after you check the resistance reading of the IC, then solder in the resistor, and then take the voltage reading, the neagtive leg (the one with white bar is negative) of either caps will be fine, the two caps are connected in parallel.

[Deebeaux]

Re: Sanyo DP46849 46" LCD - Does not power up.

OK, that TNY274PN IC is for the standby 5v power supply. Take the resistance reading between the ground pin and the other 7 pins, report the readings.

Resistance readings are as follows. As I'm not 100% sure which one is the "ground pin" I took some various readings.

• All source pins (5-8) between other source pins are 0.12 Ohm.
• Drain (pin 4) to every other pin starts out at about 2.5XX MOhm and trickles down, it hit 2.0XX MOhm and kept going. The value seems to pick up where it left off when I switch from pin to pin when testing drain to anything else.
• EN/UV (pin 1) to any source (5-8) is 329.87 (330?) Ohm.
• EN/UV to BP/M (pin 2) starts at 21 kOhm and climbs
• BP/M to any source provides varying readings based which I assume are part of the logic working when jumping from pin to pin with the multimeter.

I ordered some 47 Ohm 1W resistors since I couldn't find any in my stash, so that'll have to wait a couple days. I live out in the forest and there's not really anywhere to pickup such a thing locally. Voltage readings will have to wait until then. I'll post up when I get them!

[retiredcaps]

Re: Sanyo DP46849 46" LCD - Does not power up.

Nothing looks obviously shorted with the IC.