Getting started with troubleshooting [Samsung 245BW]

[PlainBill]

Re: Getting started with troubleshooting

None of the first three caps are suitable for this purpose. They are not low ESR caps.

How much clearance do you have? This one would be ideal if you can accommodate the extra height (25mm).
35V 1000uF, 12.5mm x 20mm, P12405-ND

It is not necessary to match the dimensions of the caps; they must fit the available space, that is all.

PlainBill

[retiredcaps]

Re: Getting started with troubleshooting

None of the first three caps are suitable for this purpose. They are not low ESR caps.

As PlainBill mentions those caps chosen are not low ESR. Even before the Japan situation, both mouser and digikey for some reason are getting low or have no stock on popular low ESR caps like Panasonic FR or FM.

These low ESR caps have a 26 week leadtime according to digikey and mouser.

Maybe you should just change those small SMPS startup caps and see if the TV works. If it works, place your order and wait 26 weeks?

[PCBONEZ]

Re: Getting started with troubleshooting

Also you didn't mention the manufacturer and series of the old caps.
-
ESR and Ripple specs vary widely even within the realm of low ESR caps.
Can't do an equivalency check without knowing what the old ones are.
.

[nerdbot]

Re: Getting started with troubleshooting

Also you didn't mention the manufacturer and series of the old caps.

Sorry, the manufacturer of the caps for the 245BW is Samwha. It's a bit late here, but I can get the series of each capacitor tomorrow.

As PlainBill mentions those caps chosen are not low ESR. Even before the Japan situation, both mouser and digikey for some reason are getting low or have no stock on popular low ESR caps like Panasonic FR or FM.

These low ESR caps have a 26 week leadtime according to digikey and mouser.

Maybe you should just change those small SMPS startup caps and see if the TV works. If it works, place your order and wait 26 weeks?

Haha, yeah maybe. Though once I get it back together, I'll be less inclined to take it apart again, but I guess it's better than not having a working monitor for 26 weeks.

[nerdbot]

Re: Getting started with troubleshooting

Here is everything I could see on the labels of the 3 caps in question:

35V 1000uF, 12.5mm x 20mm, 105C
SamWha RD VNA PET

35V 470uF, 10mm x 18mm, 105C
SamWha RD W4E

10V 1000uF, 10mm x 14mm, 105C
SamWha RD W1A PET

[nerdbot]

Re: Getting started with troubleshooting

Well, I've got some good news and some bad news.

The good news is that my 204B is repaired and working again.

The bad news is that the 245BW still is not. I replaced all the caps on the power board (except for the big 450V 82uF center capacitor). However, when I connect everything back up, the power light still doesn't come on. When I measured the voltage on the S_B pin on the power board, it still reads around 4.3V. However, I did notice the following:

- With the bezel power button+ logic board + power board are connected, the S_B pin voltage does dip toggle between ~3V and ~4V when I push the bezel power button.

- If I don't connect the logic board, and just measure the S_B pin of the power board by itself, then I get a solid 5.3V

Any suggestions?

[retiredcaps]

Re: Getting started with troubleshooting

However, when I connect everything back up, the power light still doesn't come on.

In post #4

https://www.badcaps.net/forum/showpo...34&postcount=4

jetadm123 suggests you check out the megathread and the resistor that seems to go bad on this particular monitor.

The megathread ...

https://www.badcaps.net/forum/showth...ighlight=245BW

[nerdbot]

Re: Getting started with troubleshooting

Yeah, I've been reading through the thread trying to make heads or tails from all that has been discussed in that thread. I guess after I've digested it all, I'll move my questions over there.

Thanks again!

[retiredcaps]

Re: Getting started with troubleshooting

I guess after I've digested it all, I'll move my questions over there.

Check RB805. It should be around 68 ohms.

[nerdbot]

Re: Getting started with troubleshooting

Hi Retiredcaps,

Sorry for the slow reply, I was reading the megathread a few times and also looking for pictures referencing RB805.

Unfortunately, my power board is different than the one most people have in the 245BW megathread. Mine is a BN44-00195A, whereas it seems most people are referring to the BN44-00173A board in the megathread.

I looked at the picture in this post to get an idea of the general area to look in:
https://www.badcaps.net/forum/showpo...4&postcount=37

That general area on my board seems to be where PlainBill and newbie1 identified the SMPS chip, and PlainBill suggested I replace those 3 capacitors. In that area on my board, I was able to identify the following resistors:

(Identified from the top of the board)
RB801
RB802
RB803
RB808

(Identified from the underside of the board)
RB804
RB813

I've attached a closeup of the underside of the board beneath the SMPS chip (STR-A6159). Then, using the link from Newbie1 as a starting point, I found the datasheet for the STR-A6159:

http://pdf1.alldatasheet.com/datashe...STR-A6159.html

I did my best to understand the datasheet, and I measured the resistance of the above mentioned resistors:



RB801 (R91 from the datasheet?) - 89k ohms
RB802 - 98k ohms
RB803 - 47 ohms
RB808 (R3 from the datasheet?) - 2.2 ohms

RB804 - 1.3 ohms
RB813 - 3.24k ohms

I'm actually not sure about RB813. When I measure it on the "20K ohms" setting, I get "3.24". But if I switch it to "200K ohms" setting, I measure "18.8"

Also, unrelated to resistance measurements, a few more observations I've made:

- As mentioned before, with no logic board attached, the S_B pin measures 5.3V

- With the logic board attached, the S_B pin almost always measures around 3.5-4.3V

- I say "almost" because if I leave the boards unpowered for a "long" time (where by unscientific measurement, "long" = overnight), and plug everything (logic board, power board, and front bezel connector) back in, I can get the standby light on the bezel to come on (solid, not blinking) and the S_B pin reads 5.3V and the 5.2V_ST pin on the logic board also registers 5.2V-5.3V. However, this only lasts for a few seconds, and the standby light goes off and the voltage on the S_B and 5.2V_ST pins go back to 3.5-4.3V. I also noticed when supplying power after leaving it off overnight, that the power button pulsates and slowly gets brighter until it turns solid - different than the normal blinking when the monitor is in "standby" mode. Also, since I'm frantically taking measurements while the power light is solid, I'm not paying attention to how it turns off. So I don't know if it slowly fades out or just shuts off.

- The 24V pins on the power board that goes to the inverter always measure 0V.

[nerdbot]

Re: Getting started with troubleshooting

Another update:

I did a lot more reading on here, mainly the threads about no power at all. First thing I did was check my fuses on my power board for continuity. I don't quite know what that means, and I'm not sure that I did it right, but here's what I did:

1. Left the fuses on the power board
2. Set my DMM to my 200 ohms
3. Touched one lead to the metal end on one side fuse, and the other lead to the other metal end on the other side of the fuse

Both fuses measured between 0.2-0.5 ohms. From the other threads I read, I heard the two possible options were either 0 ohms or infinite. Is 0.2-0.5 ohms "close enough" to 0? Or does this indicate the fuses are bad?

I also found this post from PlainBill:

https://www.badcaps.net/forum/showpo...5&postcount=15

Not quite correct.
U7 is the reset controller for the processor on the signal card. If it is bad the processor will not start, and the power LED will not come on. You WILL still have the normal voltages out of the power supply.
PlainBill

Correct me if I'm wrong, but this seems to be the scenario I'm experiencing? When it's just the power board by itself with power, the S_B pin shows 5.3V. When I connect the logic board (where I assume the reset controller is located), the S_B pin voltage drops to 3V-4.3V. Does this indicate a bad reset controller?

If so, I'm not sure how to identify which chip is the reset controller. Based off the pictures I've seen in the other threads, I see a lot of 3 pin chips (1 on one side, 2 on the other) on my logic board. Once I know where the reset controller is, I'll certainly try either removing it or the shorting out trick you guys have previously mentioned to other users here.

Finally, I was also able to locate the service manual for the 245BW and I attached a screenshot of the "No power" troubleshooting section. At step 1, I did not get 5V at pins 3, 4, or 5 of IC705.

The IC705 chip is an AnaChip AP1501 "150Khz, 3A PWM Buck DC/DC Converter", and I downloaded the datasheet:
http://www.alldatasheet.com/datashee...IP/AP1501.html

I'm at work right now, and didn't write down the exact voltage measurements of this chip from last night, but I do know it was somewhere between 2V-3.5V for pins 4 and pin 5. To measure the voltage on pins 4 and 5, I put the black lead on pin 3 (ground) and then the red lead on pins 4 and 5. Was that correct?

The flowchart was informative, but it would be nice to know what IC705, IC703, and IC310 do. I was able to locate IC705 (and find it's general description) and IC703 (not sure what it does though) on the logic board, and neither of those look like a reset controller. When I get home, I'll try to locate IC310. Is it possible that IC310 is the reset controller?

According to the troubleshooting flowchart, the lack of 5V on pins 4 and 5, I should check the SMPS, like PlainBill suggested. Since I've replaced all the caps on power board, and it seems to be functioning when it's the only thing connected, that's what lead me down the reset controller path. Was this a reasonable deduction? Or is it an open resistor on the power board? I posted some of the Ohm measurements of the resistors in the area of the SMPS controller in my previous post, but I don't know if these values are "normal" or bad. I've been trying to understand the STR-A159 datasheet to try and figure out which resistors in the diagram match with the actual resistors on the power board, but I've only been able to guess at a couple.

I feel like I'm starting to get all the various puzzle pieces to understand the problem, but not quite enough knowledge to actually complete the puzzle. Any suggestions or assistance would be greatly appreciated!

[retiredcaps]

Re: Getting started with troubleshooting

Both fuses measured between 0.2-0.5 ohms.

Your fuses are good. A good fuse should read less than 1.0 ohms.

There is always some resistance on the test leads. When you touch the two probes together, you should get something like 0.2 to 0.4 ohms.

Some of the crappy 830 multimeter variations on ebay have the cheapest possible test leads and when you touch them together, they read 0.9 ohms.

[nerdbot]

Re: Getting started with troubleshooting

Your fuses are good. A good fuse should read less than 1.0 ohms.

There is always some resistance on the test leads. When you touch the two probes together, you should get something like 0.2 to 0.4 ohms.

Some of the crappy 830 multimeter variations on ebay have the cheapest possible test leads and when you touch them together, they read 0.9 ohms.

Thanks RetiredCaps, good to know! If I may ask another, more general, question: what does it mean to "test for continuity"? I've seen it mentioned fairly often, and I believe to multiple types of components (fuses, capacitors, resistors?), and wondered if maybe I need to do that myself.

[retiredcaps]

Re: Getting started with troubleshooting

If I may ask another, more general, question: what does it mean to "test for continuity"?

Test for continuity means you are testing for a continuous path between 2 end points. A good fuse will have continuity. A bad fuse will not have continuity.

The continuity can be useful for certain tests, but the "threshold" for continuity varies GREATLY. On some of my multimeters, it is 30ohms +/- 10 ohms. On some really crappy multimeters, it is as high as 1500 ohms.

From post #13

https://www.badcaps.net/forum/showthread.php?t=10419

Multimeter
=======

If you have a manual ranging multimeter, set it to 200 (two hundred) ohms. Touch the black and red probe together. It should read 0.3 or 0.4 ohms. If it is higher than 1.0 ohm, there is something wrong with your multimeter.

If your multimeter reads "1" or "OL", it means the measurement is outside your chosen range. Don't confuse "1" on the left hand side of this display with 1.0 on the right hand side. The first means out of range and the second means 1.0 unit of your measurement.

Do NOT use the continuity or "beep" feature of your multimeter for measurements. Some multimeters "beep good" for resistance readings less than 1.5k ohms.

Always post the actual results of your measurements when asking for help.

[nerdbot]

Re: Getting started with troubleshooting

https://www.badcaps.net/forum/showthread.php?t=10419

Wow that thread is amazing! Thanks for the link and for writing that thread up in the first place

[jetadm123]

Re: Getting started with troubleshooting

I don't think a reset controller is an issue here. As PlainBill mentioned, if it is used on your monitor, then it would only come into play if your power supply is outputting 5V and 24V, which it isn't.

Interesting that you're getting the 5V standby voltage output on occasion with everything hooked up. Did you verify the correct polarity of the caps you replaced? Check for bad solder joints?

Sounds almost like there's a short on the logic board that's dragging down the standby voltage.

[PlainBill]

Re: Getting started with troubleshooting

I'm keying on the fact that you don't have a constant 5V on the S-B pin. Without the logic card (signal card) you are getting 5.3 volts, which is exactly what I would expect. When the signal card is hooked up, it drops to 4.3 volts or lower. That is a problem.

You also mentioned that the troubleshooting procedure mentioned checking for 5V at IC705. By it's description, I suspect IC705 is supposed to drop the 5.3 volt Standby supply down to 3.30 volts for the processor.

Now the problem is figuring out if the problem is the standby supply, or if there is a problem on the signal card.

PlainBill

[nerdbot]

Re: Getting started with troubleshooting [Samsung 245BW]

Interesting that you're getting the 5V standby voltage output on occasion with everything hooked up. Did you verify the correct polarity of the caps you replaced? Check for bad solder joints?

I double checked that the polarity of all the caps I replaced on the power board are correct. The solder joints I made on the power board look ok, though it is possible I'm wrong. I may try redoing some of the uglier joints if we can't get to the bottom of the issue.

I didn't do any work on the logic board thus far.

Now the problem is figuring out if the problem is the standby supply, or if there is a problem on the signal card.
PlainBill

Using Retiredcaps thread to learn about how resistors are marked, I was able to identify what each resistor on the power board should be:

Board location - Marked value - Measured value
RB801 - 100K Ohms - 98K Ohms
RB802 - 100K Ohms - 98K Ohms
RB803 - 47 Ohms - 47.3 Ohms
RB801S - 33 Ohms - 33.5 Ohms
RB808 - 2 Ohms - 2.2 Ohms

So it seems all those look good. However, there is another resistor, NE of the center cap in my power board picture, labeled RM801. From what I can tell, it should be 0.22 Ohms (red-red-silver?-gold). However, the reading I get is strange - Apparently, it's reading "0.56" when my DMM is set to the "20M" ohm range. That would mean 560K Ohms, right? I attached a picture of the resistor.

When I measure RM801, I started at the 200 setting and it quickly showed out of range. The same thing happened at the 2000, 20K, and 200K settings. When I switch to the 20M setting, it starts decreasing from a 20.0 reading, quickly at first, until it gets into the 1.0 range. At that point, it slowly decresases, getting slower and slower, and seemed to settle around the 0.50-0.60 range.

From what I read, an open resistor will show infinite resistance and a shorted resistor will show 0. This appears to be neither? Should I replace this resistor?

[nerdbot]

Re: Getting started with troubleshooting [Samsung 245BW]

As a side note, I found IC310 on the logic board. It's the big chip in the middle with the large number of tiny pins. If it gets that far, I don't think I'll be trying to replace that myself

[PlainBill]

Re: Getting started with troubleshooting [Samsung 245BW]

I double checked that the polarity of all the caps I replaced on the power board are correct. The solder joints I made on the power board look ok, though it is possible I'm wrong. I may try redoing some of the uglier joints if we can't get to the bottom of the issue.

I didn't do any work on the logic board thus far.



Using Retiredcaps thread to learn about how resistors are marked, I was able to identify what each resistor on the power board should be:

Board location - Marked value - Measured value
RB801 - 100K Ohms - 98K Ohms
RB802 - 100K Ohms - 98K Ohms
RB803 - 47 Ohms - 47.3 Ohms
RB801S - 33 Ohms - 33.5 Ohms
RB808 - 2 Ohms - 2.2 Ohms

So it seems all those look good. However, there is another resistor, NE of the center cap in my power board picture, labeled RM801. From what I can tell, it should be 0.22 Ohms (red-red-silver?-gold). However, the reading I get is strange - Apparently, it's reading "0.56" when my DMM is set to the "20M" ohm range. That would mean 560K Ohms, right? I attached a picture of the resistor.

When I measure RM801, I started at the 200 setting and it quickly showed out of range. The same thing happened at the 2000, 20K, and 200K settings. When I switch to the 20M setting, it starts decreasing from a 20.0 reading, quickly at first, until it gets into the 1.0 range. At that point, it slowly decresases, getting slower and slower, and seemed to settle around the 0.50-0.60 range.

From what I read, an open resistor will show infinite resistance and a shorted resistor will show 0. This appears to be neither? Should I replace this resistor?

I would definitely remove that resistor and test it out of circuit. If indeed it is open you have found the problem.

Short explanation. That resistor is used to sense the current in the primary side of the standby power transformer. If it's resistance is high - or it has gone completely open - the SMPS controller will reduce the current - which reduces the output voltage. With essentially no load (logic card removed) you will get full output voltage.

PlainBill