EEVblog Electronics Community Forum
Electronics => Repair => Topic started by: Srbel on August 02, 2016, 02:21:12 pm
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After taking a brake from the forum, for receiving insults, I am back. For now.
So, the water has gotten into a TV (from the top) while it was ON. It spared and since then - no picture (black screen). After like a month, I open it, water is all gone. There are marks that show where the water has been. It was not much at all.
When I turn it ON, I can hear SMPS and HV sound. There is nothing on the screen (just black, no "snow"). When I turn it off, there is a white square that shrinks into a dot in the centre of the screen, and there is a loud sound of "vacuum forming" (can not explain it better than that).
Allegedly, CRT steering coils are at fault. But I do not believe that. I measure about 2-2,5 ohms on one, and about 13 ohms on the other. I don't believe that it got to 13 ohms by water damage, I think that it got there gradually with time (TV is from 1987.).
What do you think is the problem? What are the normal resistance values for those coils?
Steering coils:
(http://www.mgelectronic.rs/content/images/thumbs/0065561_TVOTKL.jpg.jpeg)
An actual TV:
https://s32.postimg.org/h3zg3ayyd/IMG_20160801_140524.jpg (https://s32.postimg.org/h3zg3ayyd/IMG_20160801_140524.jpg)
https://s32.postimg.org/nmsag8b5h/IMG_20160801_140120.jpg (https://s32.postimg.org/nmsag8b5h/IMG_20160801_140120.jpg)
https://s32.postimg.org/8o9vlsw39/IMG_20160801_140332.jpg (https://s32.postimg.org/8o9vlsw39/IMG_20160801_140332.jpg)
https://s32.postimg.org/4qmlwe99x/IMG_20160801_140425.jpg (https://s32.postimg.org/4qmlwe99x/IMG_20160801_140425.jpg)
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Electron gun/signal problem.
That you get a white square indicates you do have proper function in the deflection coils.
So what should you do ?
Clean the muck off the PCBs for a start, that white residue can be conductive.
At a guess you have no signal getting to the PCB attached to the neck of the tube, how far back that lack of signal goes is something you need to figure out.
Try not to fry yourself.
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Thanks. Unfortunately, I can not clean it (there is a lot of dust). I mean I have no place to go to clean it. :/
P.S. Pushing the ON/OFF button a few times is not enough to discharge the CRT? Should be for capacitor, but CRT? :/
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When I try it with coils disconnected from the main board, nothing happens. I turn it on, and there is no picture, no dot, not even power supply sound. When I switch it off, also nothing (there is no longer that sound and square).
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If no audio, not even static (is this an old-style broadcast TV (composite video input, etc.?)), look at SMPS output voltages, supply to ICs in audio section. I would not be focusing on the HV or steering circuits if there was no audio.
Can you input a signal to the audio inputs (from signal gen, or radio or VCR. (c; )
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I have tested it without an input signal (antenna). I was talking about PSU sound (buzzing), not sound from the speakers.
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As a starting point you will have to clean the thing, and check all connectors for oxidation/clean it. Inclucding tube end PCB.
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Just not possible. I live in a flat, not in a house.
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Repairing a CRT TV is not very useful anymore. They are just outdated and just to power hungry and usually no SAT / DVBT.
With a little luck you get used ones, still working for very little money or even free. I just send a working one to recycling as nobody wanted it, even for free.
It could be just dirt causing sparks - so if you are lucky cleaning could be enough. But these sparks could also do some damage (e.g. burn marks on board that stay conductive, damage isolation) that is hard to repair.
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Just not possible. I live in a flat, not in a house.
You might not want to take an air compressor and blow the whole crap, but how does that prevent you from carefully scrubbing everything?
Without cleaning it will be hard to find where the dirt and water may or may not have caused unwanted current paths.
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Take the tv outside and clean it there ????
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Sound like dust and moisture on crt panel, particularly around the screen grid resistors.Or resistor itself O/C, usually around 270K.
Check voltages on crt socket. Momentarily short one of the cathodes to deck with a 1K resistor and you should get that colour very bright raster.
Cheers, JJ
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I have tested it without an input signal (antenna). I was talking about PSU sound (buzzing), not sound from the speakers.
It would be helpful to know if the TV will take an audio signal and play it through the speakers. Then we might know that the problem is isolated to video and HV.
If you can't clean it, if you can't plug in some audio, we're limited in how we can help you. We can't fix it for you. ;)
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Thanks. Unfortunately, I can not clean it (there is a lot of dust). I mean I have no place to go to clean it. :/
P.S. Pushing the ON/OFF button a few times is not enough to discharge the CRT? Should be for capacitor, but CRT? :/
A vacuum cleaner and a 1" paint brush to agitate loose the dust will take care of it with minimal disturbance.
A damp rag around the tube and then tooth brush and some IPA for the PCBs affected.
And remember the tube will not discharge straight away and needs to be left for some time before you get near it with the damp rag!!!. (the power switch will not make any difference to this CRT charge).
Given you get a white dot means the HV is functional. As stated before the scan drive is not getting to the deflection coils (which I would say are probably okay).
After vacuuming the dust away check for bad /corroded connectors as others have suggested etc.
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I will see if I can clean it a bit. :/
I don’t have any antenna output. I have an IPTV in my flat, and this TV only has classic antenna input. I don’t even have room (indoor) antenna to try it with.
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OK, I have cleaned it. With a brush and a vacuum cleaner. But there was a lot of stuck dirt on the main board that could not be cleaned this way, so I had to disassemble the boards, and wash the main one with water in the shower. :/
So, in the next few days, until it is completely dry, no repairs...
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:clap: :-+
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The board is completely dry now. But there is limescale residue from the water. Do I need to clean that too?
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Given the high voltages present in a CRT television set, sometimes a few hundreds of ohms created by residue can create a path for current to flow. Therefore, the ideal scenario is to get the board looking like new...
I don't know how bad the residue is in the board, but where I live the residue only from the water is very minimal - on the other hand, where my parents live (close to the sea), the residue is like a short circuit (few ohms).
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I have used tap-water. The same water I drink.
I will see if I can clean it with alcohol and a brush. But all that brushing and also that vacuum-cleaner, I'm afraid not to kill something with static. I don't have an anti-static brush. :/
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OK, I have assembled the TV. I have also found a broken trace on the main board, and repaired it.
Now, when I turn on the TV, there is still nothing on the screen (no antenna, so it should show "snow"/static).
But, the difference from before is that now the LED screen (that shows what TV channel is selected) works, and when I change the channels it shows that. Also, when I turn off the TV, now there is no white square that shrinks into a dot, and there is no loud sound of vacuum. Now it sounds normally when turned off. Remote control works.
But the screen is actually OFF. It remains completely the same whether the TV in on or off. :/
Also, there is some cracking heard from the speaker.
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Never ever wash a pcb in the shower. Tap water isn't just H2O. Even if you dry it afterwards, there will remain residues on the board and most probably also in some parts.
Next, there could be parts on the pcb which must not be submerged because it will cause dammage inside the part. Then there are parts where the water will get in but you won't ever get the water back out.
For me it sounds like you have no clue what you are doing.
Said that, I highly recommend, don't play around with high voltage devices! Involve someone who has the knowledge or just buy a new tv set.
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Never ever wash a pcb in the shower. Tap water isn't just H2O. Even if you dry it afterwards, there will remain residues on the board and most probably also in some parts.
Next, there could be parts on the pcb which must not be submerged because it will cause dammage inside the part. Then there are parts where the water will get in but you won't ever get the water back out.
For me it sounds like you have no clue what you are doing.
Said that, I highly recommend, don't play around with high voltage devices! Involve someone who has the knowledge or just buy a new tv set.
Stop pretending you are smart, and that I am clueless. It is easy to do that over the internet, but in person you would not be able to do that to me and just walk away. If you have nothing helpful to say, leave.
This is the kind of people that made me leave this forum for months.
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Sorry mate,
not just pretending. I worked as a professional radio & television technician for 15 years. After that i made a degree in electronics engineering.
I pretty well know what I'm talking about.
Cleaning a tv means, take a vac a brush und eventually some alcohol but never ever use tap water to rinse or submerge the board.
You also seem to have no idea if and how long a tube holds its hv and how to safely discharge it PRIOR to any work on the tv set.
The resistance of H & V deflection coils are different of course.
All that are fundamental basics.
And no, i didn't say you are dumb, you just don't know how to work on tv sets and that can be dangerous and in most of the cases it does not lead back to a working tv.
By the way, if we would have had this discussion face to face I would have given you the same advice.
Sorry, if sounding rude. I'm not a native speaker.
73
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I am not going to read your BS. Go harass someone else. You are not smarter than me. You know nothing about me. Go away. You are not helping.
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Hi
Never ever wash a pcb in the shower. Tap water isn't just H2O. Even if you dry it afterwards, there will remain residues on the board and most probably also in some parts.
I both agree and disagree :
I have heard of some manufactures recommending boards be washed with water (yes normal tap water), these were ink jet printer manufacturers. As you can imagine, if a ink cartridge leaked it would leave a horrible mess on the PCBs.
I agree that washing a PCB which has high tension (another term for Very High Voltages) is probably not a good idea since lime scale residue could be a break down path. :-\
I am not going to read your BS. Go harass someone else.
Please do not take comment so personally.
When ever you post to a public forum, you are going to get some people who will say nasty things. It is a sad :( matter of fact.
There are many people here all very friendly and trying to help. ;)
There are some that do not mean to be unfriendly but unfortunately the nature of their personality means they say things which they do not mean to be offensive but come out that way. Many engineers are socially awkward and say things matter of factually no matter how offensive it may sound to others. None of it is meant to be offensive or personal.
It sounds like there is some progress with your repair.
When you turn on the TV, can you feel static build up on the front of the CRT ? (indication of HT on the screen - cathode to annode electron acceleration)
(I do not remember from the first post) Did the water damage happen when the TV was turned on (this may have damaged components) ?
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Never ever wash a pcb in the shower. Tap water isn't just H2O. Even if you dry it afterwards, there will remain residues on the board and most probably also in some parts.
Next, there could be parts on the pcb which must not be submerged because it will cause dammage inside the part. Then there are parts where the water will get in but you won't ever get the water back out.
For me it sounds like you have no clue what you are doing.
Said that, I highly recommend, don't play around with high voltage devices! Involve someone who has the knowledge or just buy a new tv set.
That is absolutely not true. For example: http://assets.fluke.com/manuals/8842a___imeng0300.pdf (http://assets.fluke.com/manuals/8842a___imeng0300.pdf)
Quote section 6-77.
6-77. Cleaning Printed Circuit Assemblies
If conditions warrant, individual printed circuit assemblies (PCAs) can be cleaned with
water-based commercial cleaning systems such as dishwashers. If such systems are used,
observe the following precautions:
1. Remove all shield covers (applies to the True RMS AC PCA) and socketed ICs.
2. Use Reagent Grade 2 or better water (de-ionized or distilled water) for the final rinse
in geographic areas with exceptionally hard water. During the final rinse, spray or
run the water so that the surface is thoroughly covered to remove all ionized material.
3. Thoroughly dry all PCAs using one of the following methods:
a. Preferably, the PCA should be dried in a low-temperature drying chamber or
infrared drying rack with a temperature range of 49°C to 72°C (120°F to 160°F).
b. If neither a drying chamber nor a drying rack is available, air dry the PCA at
ambient room temperature for at least two days.
A satisfactory cleaning method consists of holding the PCAs under hot running water
until they are clean. Follow this wash with a final rinse. (See consideration 2, above.)
I'm pretty sure Fluke knows how to handle a precision instrument. I have read similar directions in Tek and HP service manuals too.
There are components, that should not be washed, for example in many Tek scopes the attenutator assembly has "Do not was in water" warning. But such a consumer electronic stuff, like a tv could be washed with no problem whatsoever. Of course, you have to dry it properly.
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The water got in while TV was on, yes. Something sparked inside, and then it was unplugged. After a few weeks, I took it to try to repair it.
There is some static I can feel on the front of the CRT when it is on. I placed a palm of my hand so the back of it touches (nearly touches) the glass, and I can feel static on the hairs.
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no oldschool monitor engineers here i see! (other than me)
what make / model is it?
all crt system repair is similar.
first you test the psu, by isolating it from the high-voltage and loading it.
you need to find the B+ line from the psu to the line-output transformer.
it usually has a 100-200v electrolytic across it and an inductor afterwards.
you lift the inductor if it's *after* the electrolytic so the cap is still in the circuit.
then solder a couple of wires across the cap and connect them to a 60w 240v lamp bulb - a normal one - NOT halogen or ccfl etc.
when you turn the tv on, the lamp should light and stay on with a stable brightness.
and you can meter the voltage across it - it is sometimes ajustable.
be warned - it's going to be 80-160v dc
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It is 1987. Philips 20CT6350.
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2. Use Reagent Grade 2 or better water (de-ionized or distilled water) for the final rinse
in geographic areas with exceptionally hard water. During the final rinse, spray or
run the water so that the surface is thoroughly covered to remove all ionized material.
Sure its common practice to clean pcbs with water based cleaning systems but of course, these DO NOT use tap water.
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Sure its common practice to clean pcbs with water based cleaning systems but of course, these DO NOT use tap water.
Sorry, have to disagree. Depends on the application of the PCB.
For TV or anything that have high voltage - yes definitely.
I worked as a professional radio & television technician for 15 years. After that i made a degree in electronics engineering.
So, yes from your background, it is standard to NOT clean PCBs in water.
(FYI I am a Chartered Engineer (CEng) with a BEng in Electrical and Electronic Engineers - so please do not tell me I do not know)
Long ago, before I went to read for my degree, I spend my summer working for an electronics service company. I worked on servicing Electronic Cash Points. They had an industrial machine cleaner - just like a giant dish washer with a flip top lid. We would put the cash point shells, including the LED displays into this machine. Had to wait for 24h for them to dry but no problems after that. They were CHEAP, so I would guess that they did NOT use deionised water!
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It is 1987. Philips 20CT6350.
chassis is CTO-S OR CTO-N
what number is after "20CT6350/" ?
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It is /50R
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so it's the "CTO-S" chassis.
http://elektrotanya.com/philips_chassis_cto-s.pdf/download.html (http://elektrotanya.com/philips_chassis_cto-s.pdf/download.html)
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It seems that after assembliing it back, I have connected one of the cable to the wrong connector. But I don't know which one!
There is this connector on the main board, next to the HV transformer, that is empty. But there are no loose cables.
(left from the HV transformer, under the blue electrolytic caps):
https://s32.postimg.org/mu3rl4vph/IMG_20160805_164156.jpg
I am looking at the original pictures from the first post, but I can not see what should go where.
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so it's the "CTO-S" chassis.
http://elektrotanya.com/philips_chassis_cto-s.pdf/download.html (http://elektrotanya.com/philips_chassis_cto-s.pdf/download.html)
I have an original schematics. It came with the TV.
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I'm not saying you dont know, also I don't intend to argue. These "Dishwashers" are quite common in electronics industry but normally they have some kind of "de-ionising" device built in or attached to it and do monitor the conductance of the water. The system rinses the pcbs until conductance is below a predefined level. These machines still look like regular dishwashers.
Maybe this is different in areas where the water hardness is already below this limit without de-ionizing but at least in europe this is not the case.
Would you agree, that tap water contains different salts which can lead to corrosion? So in general its better to avoid cleaning pcbs with tap water without rinsing with deionized water at the end?
Again, I do not intend to be rude. Please blame it to my disability to find proper words in english.
73
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OK, I think that connector is for power to the PCB that goes on the back of the CRT. By accident, I have connected that cable to one of the boards in the socket on the left, so CRT board did not get any power. Now it should. But, I don't know what is the empty connector on that daughter board for. Connector is dirty on the inside, so nothing was plugged in from the beginning.
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OK, I have "snow"/static on the screen now. It seems to behave normally. I just have to get it back to the original location, and try it out with an antenna. But I think it is fixed now.
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These "Dishwashers" are quite common in electronics industry but normally they have some kind of "de-ionising" device built in or attached to it and do monitor the conductance of the water. The system rinses the pcbs until conductance is below a predefined level.
Maybe this is different in areas where the water hardness is already below this limit without de-ionizing but at least in europe this is not the case.
That company was so cheap and skimped on everything, they even made us re-form springs instead of using new springs :palm:
I was very young back then and I did not know about such things as the machine washer. I did not notice anything to measure the water. I do remember the big cut off value plumbed into what looked like the regular tap water supply, though it was only used to top up the machine.
Would you agree, that tap water contains different salts which can lead to corrosion?
Yes, absolutely.
I do not know what long term effects these residues have on electronics.
I know certain sectors do recommend washing in normal tap water (ie the printer manufacturers). They are not worried about longevity >:(
So in general its better to avoid cleaning pcbs with tap water without rinsing with deionized water at the end?
I guess, if you want to have the thing still working in 30 years plus - yes a good idea.
Again, I do not intend to be rude. Please blame it to my disability to find proper words in english.
No worries. Like I said, I guessed from your background that it is a no no to wash in tap water.
The company I work at now definitely does not wash in tap water, I think they use cleaners and solvents.
Your English is pretty good. Better than my German/Austrian. :-+
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OK, I have "snow"/static on the screen now. It seems to behave normally. I just have to get it back to the original location, and try it out with an antenna. But I think it is fixed now.
:-+
8)
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2. Use Reagent Grade 2 or better water (de-ionized or distilled water) for the final rinse
in geographic areas with exceptionally hard water. During the final rinse, spray or
run the water so that the surface is thoroughly covered to remove all ionized material.
Sure its common practice to clean pcbs with water based cleaning systems but of course, these DO NOT use tap water.
Have you even read what it writes? It suggests using deinonized water for *final rinse* and only in areas where normal tap water it exceptionally hard.
Of course it does not hurt to use deinonized water, but for sure you won't have any problem on a TV set. Especially if you blow most of the water off. You will have very little deposit. If you want to be really celan, follow up with a rinse with IPA, it'll take the water with it.
I have cleaned numerous PCBs and whole instruments in normal TAP water, they are still fine.
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Hmm, after about 30 seconds from turning on, screen goes from white static to purple. Needs degaussing, or?
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your losing green - trace the green signal from the tube base - could be a bad solder joint.
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This is how it looks now. Goes straight to the purple now, and the picture of static is not "stable":
http://www.megafileupload.com/7ik4/VID_20160806_090717.3gp.7z (http://www.megafileupload.com/7ik4/VID_20160806_090717.3gp.7z)
Also, I hear crackling sound from the base of the CRT.
I will try to find cold solder joints, but I don't see any on the PCB that goes on the back of the CRT.
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I have traced G line (for green colour) and there are no cold solder joints. I have also re-soldered some critical joints.
I have measured voltages at the output (for R, G and B) of the "Chrominance + Luminance - PAL" board (that sends signals to the PCB on the back of the CRT). It says in the schematics that those voltages should be 5V. I have measured 4,4V when the CRT board is disconnected from this board, and 2,45V when it is connected. It is the same for all 3 outputs (R, G and B). The IC is TDA3561A.
Also, now the CRT does not work at all again. I don't know why. :(
Edit: I have measured those voltages at DC, but now I see in datasheet that it says that those are p-p values. -.-
Edit 2: Measured on AC, I get about 300mV, so it is not a valid measurement (multimeter can only measure AC at 400 Hz max, I think)
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When I disconnect the RGB signals from the PCB at the back of the CRT, CRT works. I get static. It has horizontal lines which move left-right fast. The colour is between white and blue.
It looks different colour on the photograph, plus ignore 3 big diagonal lines (those are from the camera):
(https://s7.postimg.org/gbfrvb9qj/IMG_20160807_135733.jpg)
Does this mean that RGB (so called: "Chrominance + Luminance - PAL" board) is faulty?
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what happens if you feed it an RGB signal on the scart input?
and how about any OSD text?
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There is no SCART input. just a classic antenna coaxial input (I don't know how it is called).
Oh, and with "Chrominance + Luminance - PAL" board RGB output connected to the CRT PCB (the PCB that goes on the neck of the CRT), the CRT is just black. It does not even turn on it seems.
I am not feeding any outside signals, just disconnecting and connecting signal cable from the internal boards.
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a trick i used to use is swapping 2 colours over at the point of origin - in this case the rgb matrix decoder - to see if the colour on the screen changes.
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Ah, the connector is asymmetrical, so it only fits in one orientation.
The problem is that I only get something on the screen if those colour signals are disconnected. When I plug them back in, I get nothing on the screen. :/
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check any white or gray resistors on the rgb pcb, philips used resistors as fuses.
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There is one, and it is fine. Measures 15 ohms.
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Any more ideas?
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I am stuck. I don't know what board is at fault. I don't know how CRT should behave, what signals it should get and so on. And this is the last day I can use for repair. After this, I have no more time for it. :(
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check all the psu voltages against the schematic.
if you have HT then the problem is in the decoding or gun-drive area.
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There are hundreds of voltages in schematics. They are not accessible (no test points). I would need to hunt down a certain capacitors on the PCB and then solder a wire on the bottom side, then get everything back in place in order to measure it. I dont want to poke around with a few 10s of KV present.
I don't know what HT stands for.
Thanks for help, but time is up. So, I have to give up. :(
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I don't know what HT stands for.
High Tension.
Tension is another term used for very high voltages.