Getting started with troubleshooting [Samsung 245BW]

[nerdbot]

Re: Getting started with troubleshooting [Samsung 245BW]

Well, I guess I am insane - I tried the same thing, but expected a different result. I put in the 1W 0.22 ohm resistor, and that popped instantly as well. I'm trying to follow the traces on the board and work my way back towards the power supply to figure out what along the path could be causing this resistor to blow, but I'm getting lost along the way.

I took a look at RetiredCaps thread again, and I tested everything that I could find on the board (diodes, transistors, MOSFETs, resistors) and they all seem to be ok. I'm all out of ideas at this point, any other suggestions you guys could provide would be much appreciated. Thanks!

[nerdbot]

Re: Getting started with troubleshooting [Samsung 245BW]

Well, I got curious and I pulled RB801 and RB802 and tested them out of circuit. They both test just fine in both directions when out of circuit so I'm guessing those aren't an issue.

I'm going to go pick up a higher Watt 0.22 ohm resistor today and put that in tonight and see if that helps. If that one blows too... I guess that means it's something else entirely?

[nerdbot]

Re: Getting started with troubleshooting [Samsung 245BW]

Sigh, well that wasn't good.

I put in the new resistor, and turned on the power supply (by itself with nothing else connected) and within seconds, POP! The new resistor popped. I'm guessing that means I should've gone with the 1W resistor? I also noticed that the original resistor was ceramic coated, and the resistors I purchased were metal (or at least had a glossier look). Is this an issue?

I removed the RM801 resistor again, and I'm not sure if I'm paranoid or what, but I noticed that a component right next to it had a little black on the lead. I've attached a picture of it, it's labeled BM801. It doesn't look like the other diodes or jumpers on the board... diodes seem to start with "DM", "DB" or DP" and the jumpers start with "J". Just trying to figure out what it is so I can determine how to check if it's damaged.

Also, after the RM801 resistor popped, I decided to check to see if any of the other resistors were damaged and rechecked all their resistances. They all checked out fine, except I noticed something interesting with resistors RB801 and RB802 (the ones to the NE of the SMPS chip). Depending on which "direction" I measured the resistance, I got different values. I attached a picture with the leads labelled.

RB802:
Black lead on "A", Red lead on "B": 18.8 kOhms
Red lead on "A", Black lead on "B": 98.0 kOhms

RB801:
Black lead on "C", Red lead on "D": 99.1 kOhms
Red lead on "C", Black lead on "D": 88.5 kOhms

I retested all the other resistors and confirmed they have the same resistance (within tolerance) regardless of "direction".

I'm not sure how I missed this before... regardless, I'm not sure what this means. Does this mean that RB801 and RB802 are also bad?

Glad to see that you were able to find the resistor locally. The brown stuff you're referring to is an adhesive used to hold the resistor in place during the soldering process. No need to replace.

I don't mean the gunk on the resistor and the board. I mean it looks like there's a brown "sheathing" on the lead itself. I attached a picture of RM801 again, with the part I'm referring to circled in red. Is that heatshrink insulation?

[jetadm123]

Re: Getting started with troubleshooting [Samsung 245BW]

I just picked up two 0.22 ohm 0.5W resistors from the store ($1.50). They look to be the same size as my original resistor, and the 1W versions were a bit big. The lady mentioned something to me that didnt really register until i left. She said i could go up to 1W and insulate the leads.

On my original resistor there is a brownish paint(?) that is coating the leads that were exposed on the topside. Is that insulating paint? Will i need some for when i put the new one in?

Glad to see that you were able to find the resistor locally. The brown stuff you're referring to is an adhesive used to hold the resistor in place during the soldering process. No need to replace.

[nerdbot]

Re: Getting started with troubleshooting [Samsung 245BW]

I just picked up two 0.22 ohm 0.5W resistors from the store ($1.50). They look to be the same size as my original resistor, and the 1W versions were a bit big. The lady mentioned something to me that didnt really register until i left. She said i could go up to 1W and insulate the leads.

On my original resistor there is a brownish paint(?) that is coating the leads that were exposed on the topside. Is that insulating paint? Will i need some for when i put the new one in?

[jetadm123]

Re: Getting started with troubleshooting [Samsung 245BW]

You never want to go lower wattage than the original. However, higher wattage is okay. The 1W you chose is out of stock. The only one I see is:

0.22ACCT-ND

Good news is that they're 37 cents each. Bad news is that you have to purchase a minimum of 10.

[nerdbot]

Re: Getting started with troubleshooting [Samsung 245BW]

For resistors of this size, it's usually the actual physical size of the resistor that determines the wattage. The higher the wattage, the larger the resistor. Measure it and see if you can match it to something on digikey.

Yes, I meant rubbing alcohol. Some members like the 90/10 stuff, but i get along fine with the 70/30. It just takes a bit longer to dry.

Hmm, well, from what I can tell it's either .5W or 1.0W. Here are the dimensions I got from the calipers I have:

Diameter (measured at the fattest end): 3.5mm
Length: 9.0mm (or just a little shy of 9)

And it seems like either of these could be right:
RSMF1JBR220-ND
RSF12JBR220-ND

So, with capacitors, it's safe to go up with a higher voltage. Is there a similar rule with resistors? Would I be playing it safe by getting either higher or lower wattage than the original resistor, or is it critical that it be the exact same wattage?

[jetadm123]

Re: Getting started with troubleshooting [Samsung 245BW]

What markings should I look for to determine the wattage of the resistor?

While the electronic supply store in my town has been great with giving me advice on how to solder, when I asked what brands/types of capacitors they carried, they said "it didn't matter they are all the same". Out of curiosity, I bought a couple capacitors for my 204B monitor repair, and they were Nichicon VZs. Needless to say, I ended up buying the right ones from Digikey and used those instead.

Basically, I'm not completely comfortable deferring completing to their judgement on this.

Also, is rubbing alcohol what you meant?

For resistors of this size, it's usually the actual physical size of the resistor that determines the wattage. The higher the wattage, the larger the resistor. Measure it and see if you can match it to something on digikey.

Yes, I meant rubbing alcohol. Some members like the 90/10 stuff, but i get along fine with the 70/30. It just takes a bit longer to dry.

[nerdbot]

Re: Getting started with troubleshooting [Samsung 245BW]

Be sure to take the old resistor as a sample as it's hard to tell from the photo what wattage it is. Maybe 1W?

The black stuff is probably burnt rosin from the braid. Q-tip dipped in alcohol should work to clean it off.

What markings should I look for to determine the wattage of the resistor?

While the electronic supply store in my town has been great with giving me advice on how to solder, when I asked what brands/types of capacitors they carried, they said "it didn't matter they are all the same". Out of curiosity, I bought a couple capacitors for my 204B monitor repair, and they were Nichicon VZs. Needless to say, I ended up buying the right ones from Digikey and used those instead.

Basically, I'm not completely comfortable deferring completing to their judgement on this.

Also, is rubbing alcohol what you meant?

[jetadm123]

Re: Getting started with troubleshooting [Samsung 245BW]

Ok, some good news and some potentially bad news -

The good news is that I removed the resistor and it appears to be open - tested it with the "20M" setting on my DMM and now it shows out of range.

Can I pick up this resistor at my local electronic supply shop (they sell capacitors, resistors)? Or do I need one with special ratings, like the capacitors, and order it from Digikey?

The potentially bad news is that when I went to remove the solder with my desoldering braid, I noticed I left behind some black residue (picture attached). I tried gently cleaning it with a Q-tip, but it wasn't coming off. If so, is there anything I can do to repair it? I'm asking because I'd like to know if there's anything else I need to pick up other than a new resistor.

No harm in trying to find it at the local supply. Radio Shack would not carry it. If you live near a Fry's, then you might have a chance. 0.22 ohm is not a standard value. Be sure to take the old resistor as a sample as it's hard to tell from the photo what wattage it is. Maybe 1W?

The black stuff is probably burnt rosin from the braid. Q-tip dipped in alcohol should work to clean it off.

[nerdbot]

Re: Getting started with troubleshooting [Samsung 245BW]

Ok, some good news and some potentially bad news -

The good news is that I removed the resistor and it appears to be open - tested it with the "20M" setting on my DMM and now it shows out of range.

Can I pick up this resistor at my local electronic supply shop (they sell capacitors, resistors)? Or do I need one with special ratings, like the capacitors, and order it from Digikey?

The potentially bad news is that when I went to remove the solder with my desoldering braid, I noticed I left behind some black residue (picture attached). I tried gently cleaning it with a Q-tip, but it wasn't coming off. If so, is there anything I can do to repair it? I'm asking because I'd like to know if there's anything else I need to pick up other than a new resistor.

[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

[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

[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?

[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

[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.

[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

[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

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

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.