Electronic Repair Questions/Answers & Testimonials -Part 43
Thank you for a very rapid response.
I have just finished a quick-and-dirty read through of you material and I must say I’m impressed.
Thank you for making it available.
Thank YOU very much, Sir ! Really great article, as all others.
hie i wish to be informed about how i can solve a probrm whch i meet tws on philip tvs crt of power led blinking the power supply uses an ic number mc44603p and am mosfet can it b the powersupply pliz reply
Power supply blinking can be caused by the primary or secondary section. Please visit this link to isolate the problem:
hi jestine! thanks for the hint! my tv now is working very well, after i change 3 bad components and made solder dry joints at EEPROM…
i got the newsletter of the November 2009. i realy don’t have any words to say about the valuable helps U are doing. i thank you again. until i get some means to get
i didnot need to measure high votage with hogh voltage test prob because the monitor didnot have a probem in it but i tied what did say only i turned off monitor power
then i put my digital multimeter on 10nanofarad to measure internal capacitor in flyback red probe on monitor anode (power off ) black wire on steel of crt monitor as aground and i see non values on multi meter but it must measure from 4.5to6nanofarad to be right and monitor work right it had no problem
thus what is the reason og this ……i dont understand and i am sure that the monitor didnnot has a problem i am sure i wait for you mr.gestine yong
Some older Monitor does not have internal capacitor in it thus you will not get any value from measuing the flyback.
Thank you Mr. Yong for the November Newsletter.
For your information, I made your website my first Internet log in site every time I launch the Internet. I read it. Your blog is a valuable source of electronic repair tips. Mr. Yong you are very wonderful. After reading your blog I got amazed how you read all the mails posted by your many members around the globe and respond to each question they ask and at the same time find time to write and send monthly newsletters to us timely. God bless you and should continue to give you this kind of energy which you are using to help other people like me.
I wish you the best as the year draws to the end.
Hi Jestine yong
With best regards to you. I am Robin from
Sir, so I owe to you.
Recently I bought a HP kit PC deal at Costco. With this kit was included a HPw2338h lcd monitor. The first monitor was defected, with a white pixel lighted. It was under garantee, and I returned it. They gave me a second monitor, but this second has another problem, it is noisy, with vibrations that come from the power supply, I think. Is there a solution to stop this noisy sound, I am not interested to return another time to Costco for this?
Noisy (high pitched sound) could be caused by transformer but when you said the monitor have vibration then i really do know what is inside the Monitor. A LCD Monitor should not vibrate unless someone installed a fan and the fan have problem. You may need to open up the monitor and check it out. Have a good day!
I am working in a Company service center,Can you give me some tips to maintain our store(Spare parts) for fast service.We Do Conv.TV,LCD,DVD,SYSTEM,MMspeaker,Home Theater service.If you have any presentaiton please sent to me,Thankyou.
I believe you have the record of equipment repaired. Just order more on the fast moving parts in your industry.
I actually thought about the UC3842, but then I wasn’t sure because:
1. There is another DIP-20 PWM IC on the PCB – labelled SG6105D BAZ338004.
2. On this Bad IC, Pins 3 and 6 are floating – not connected to anything. Can the UC3842 work like this?
If pin 3 and 6 are floating then it is not UC3842. It could be some other IC.
But please have a look at the 6105D datasheet – on the application page, there is a SG6848, with pins 3&6 floating. Maybe this will suit it – what do you think?
Well, there is chances it could be this IC but one still have to test it out because we do not have any choices left since the part number already blew up.
3. On the actual circuit of this bad IC, at pin2, there is the cathode of an orange diode with no markings visible. The diode is shorted.
Is it a good possibility that it is a 1N4148?
4. Assuming that it is a SG6848, and the chances of finding a SG6848 on the market are very small, what could be widely-available substitute?
For IC, rarely it has substitute part number.
I always use a 200W light-bulb in series when repairing – since I used to rebuild 1950’s tube radios – until I am sure that the circuit is OK – sometimes it helps, but sometimes not.
When you say “but sometimes not” meaning the power supply still blow?
I repaired my Tektronix 2465B power supply, and connected it via a light bulb – but the scope cycled on and off, until I removed the light bulb, and connected it directly to AC – then the scope worked fine. I guess the scope needed more than 200W for startup!
If it blinks with some output voltages at the secondary side then you can place a fuse to test it out. Yes you can use a 200 watt light bulb to test because you now know that the power supply would not blow again. By the way where do yo get the 200 watt light bulb?
Have a good day!
Checking these now….but cant figure out how to test them with my multi-meter. Here is what I tested and how.
1 2 3
Post 1 applied positive probe – post 3 applied negative probe = NO READING
Post 1 applied negative probe – post 3 applied positive probe = NO READING
Post 2 applied positive probe – post 1, then post 3 with negative probe = FULL READING BOTH CHECKS
Post 2 applied negative probe – post 1 then post 3 with positive prove = NO READING
WHAT IS FUNCTION OF POST 2?
Thanks for your support on my ebook. First you need to know what is the part number in the photo you shown it to me. It can be IC, transistors, schottky diode and etc. Since the photo is too small i could not read the part number. Once you know the part number then you will know what type of component is that. Assuming it is a NPN transistor then you can read my book on the NPN testing method and follow it.
Ok, I guess I don’t understand you directions in how to test a Schottky Diode. Is the Anode on the right and Cathode on the left??? The what is the middle terminal?
Schottky diode package type have two internal diodes pointing to each other. If you are using a Sanwa/Sunwa analog meter then place your black probe to the center pin and the red probe to the the other two pins (one at a time) and you should get a slightly high ohm reading (pointer will move to the right).
From my previous mail I start to assemble the model K7205 flyback tester. Since I cannot afford to buy both of them, so I decided to assemble with the use of assembly manual from Dick Smith.
My question is, here in our place
How can I replace substitute for the below.
A. I cannot find this kind of capacitors and its voltage.
1. 0.047uF MKT
2. 0.01uF MKT
B. Is it ok to replace round LED instead of rectangular
Thanks in advance.
Yes you can try other type of capacitor but the value have to be the same. Yes you can use a round LED instead the rectangular type.
Thanks for yor book and the hints.
I am hardware enginner which try to fix my monitor but I don’t have the schematic diagrams.
Do you have some expiriance with HP 1902 LCD monitor. The power will not
turn on. What is a typical problem with such minitors, it can also be one of the
Sorry i do not have a schematic. First you need to make sure that there is no output from the SMPS. Then check on all the componenst in the primary power side. If there are some voltages chances is high is not in the primary power part. You may need to check on the secondary side as a shorted component in the secondary side could cause a no power symptom. By the way, yes, bad capacitors could cause such symptom too. Hope this helps!
Got bad news. I went to maplin bought a capacitor for £1.40.
Installed the capacitor. No luck. The cover cannot close because the capacitor is a bit taller.
When I tested the old capacitor on ohm, the needle went up and came down very quick. Not sure whether that is normal or not.
Yes it is normal but to accurately test an e-cap you need an ESR meter.
Hard to tell. I tested on other cap. the needle came down slowly.
Different cap have different reading
Anyway, I think I have given it up for good. I cannot find the fault.
After putting the old cap. back, I used the hair dryer again and the t.v works o.k.
That is all I want to tell you. Unless you know where is the fault.
Could be anything.
It could be the corresponding components that are connected to the cap.
I would like to ask something about your schematic diagram of zener diode tester,Is it the “red probe to cathode” connected to the adj and Vout pin of LM317T? You could check it to the attached file here.i encircled it so you could see the connection that i am trying to clarify coz im planning to build one..and sir,
Yes it is connected and have many of the ERG members had shown it to me about this tester.
is it ok to use a linear transformer that has an output of 29Vac,1.3amp instead of two 12Vac,1amp?I hope you can help me sir
29 VAC transformer would be too high and afraid it will destroy LM317TIC. You can get a 24 VAC instead of 29Vac transformer.
Since I’m not very sure the problem was with vertical IC and I want to know what is the real culprit, yesterday I replaced back the original vertical IC and the monitor is still OK, and now it is under burning test.
Good to hear that it is working
About the BE junction of a transistor in this monitor that has 1.4V, after examining the circuit, I found there are two diodes connected between the junction, so no wonder it was not 0.6V.
Yes the corresponding components could contribute to why you got 1.4 volt.
And this is the first time that I found the primary winding pins of the FBT is not adjacent to each other but I’m not very sure.. Do you think this is normal/true? I don’t get what do you mean. Could you elaborate?
I mean do you think it is possible to find the primary winding pins of a FBT not close to each other? For example pin 2& 5? ( instead of for example pin 2&3 ).
Yes very common. I have seen between pin 2 and 8 , pin 1 and 6 and etc.
This monitor is using LM1246 as its RGB preamp, the output of its RGB voltage is a bit lower than its input. Do you think this is normal or any RGB preamps are always attenuating?
Different pre-amp IC will produce different voltages.
When we look at the datasheet of an IC, say for example this TDA8172 vertical IC, and find its pin 4 is ground. Could we know for sure that in its real application circuit of this IC, the pin 4 is always directly connected to ground, or it might be first connected to some other components and then to ground?
There are some possibilities. The application is just a general Info and Monitor designers could add some circuits before to the ground. However the IC heatsink is always to ground.
How about the ground pin connection of other ICs in monitor circuit, is it directly connected to ground or might be connected to some other components then to ground?
That depends on the Monitor design and if you have the schematic diagram then it will be the best.
I should have checked myself about this pin 4 of this vertical IC, but forgot and already closed the cover. I’m asking this because sometimes I find the voltage reading of ground pin of an IC is not close to zero.
Some digital multimeters when you test on ground it will show some voltage in millivolt reading.
Sir, Good day to you.
I just want to ask help how can i repair the tv model sony ( 1998 model ) cause the problem is that the horizontal and vertical pictures became very small and it takes 30 minutes to appear the picture. very small and almost dead picture ( no appearance ). What is the cause of this? Can your guide me how to locate this problem and please send me a guide or actual parts where i can locate this problem.
Thank you and God bless.
Ronald of the
Make sure the output of the power supply is steady and good. If not then you may need to check on the power supply area.
Hi Mr. Yong,
I finally proceeded to the different voltage tests and everything went without any problem. Thanks to you (I mean, to your invaluable knowledge, experience, books, and personal help).
Here’s my analysis and the tests results.
First, on the test bench, when I powered on the monitor, everything was working just fine. The display appears (CCFLs light up) and remain “on” just like a brand new LCD monitor. The “power-on-with-no-display” problem did not occur.
But, at that time, something caught my attention. Since this was my first up close and personal meeting with a live IC board, I noticed that a fairly loud sound was coming from the electrolytic capacitors, especially from the three lined up ones (see “Image_9” and hear “Sound_1” – the recording has been taken with a microphone hanging just over those the three lined up electrolytic capacitors – and see “Image_10” for a sound description). When powered on, the sound comes in fairly loud and slowly fade out (as you can hear). Then, at an unregulated pace, sometimes it slowly comes in and slowly goes out. A bit like the waves sound coming on a beach. After being “on” for a few minutes, the sound remains and stay at medium level; just enough to hear it. Is it a normal sound behaviour for electrolytic capacitors?
From the photos you have sent it seems like these three caps was bit buldge. Hope that I’m not wrong. I suggest that you replace the three e-caps and retest.
After this electrolytic capacitors sound encounter, I started to run the voltage tests. Just like you recommended, I first checked the start circuit’s “on/off” pin signal’s voltage. This test gives me a steady 2.85 volts. According to what you said in your book “LCD Monitor Repair”, on page 47, this should be a normal result. Right?
Yes that’s right!
Then, I went on to the 13/15 volts start circuit pin. When the monitor is powered on, the reading is 13.92 volts and slowly increase (over a period of ±5 minutes) to a steady 14.06 volts. Since the diagram’s rating is 13 volts and the IC board’s rating is 15 volts, is it a normal voltage value?
Sometimes it may have tolerance.
Also, is the slowly increasing voltage value is normal?
If it stays at that voltage and no more increasing then it is ok. However, because of sometime when cap have problem it may take longer time for it to charge up. I suggest that if you suspect any unusual behavior in electronic components just direct replace and retest.
Now, about the inverter’s IC VCC pin. It shows the same “increasing” behaviour as the 13/15 volts start circuit pin. It starts at 13.75 volts and slowly increase (over a period of ±5 minutes) to a steady 14.04 volts. Again, is it a normal voltage value? Again, is the slowly increasing voltage value is normal?
Same answer as above.
So, just like I said at the beginning, right now the monitor is working just fine. The “power-on-with-no-display” problem just does not occur. I remember that in the report “How To Easily Repair Intermittent Problems In Electronic Circuits”, that came with your book “Testing Electronic Components”, you explain that an overheating component in its encasing can no longer overheat when it is out of its encasing. So, to replicate the problem we must “manually” overheat the component. Which I did.
First, I took the surface temperature from most of the components (see “Image_11”), using my Tenma 72-2060 thermometer and its thermal surface probe. Then, I used my heat gun to heat the whole IC board until the ambient temperature (NOT the temperature of each component) reaches 70 degrees Celsius. Event at this temperature, the “power-on-with-no-display” problem refused to occur.
So, this new testing experience brings to my mind the following two questions:
1) Is the temperature written on each electrolytic capacitor is the maximum tolerance temperature before failure?
Yes but it still could withstand for a certain amount of time before failure.
If it is, they are all way under the maximum tolerance temperature. All of the electrolytic capacitors are rated at 105 degrees Celsius and the two Carli (yellow squared) metallized polypropylene film capacitors are rated at 100 degrees Celsius.
2) Should I heated up more the IC board (like up to 80 or 90 degrees Celsius)?
No not encourage. Sometimes a too hot temperature could kill a workable IC and related components.
Now, except for the overheating test, is there any other things I can do to try to replicate the “power-on-with-no-display” problem or should I just return the monitor to its owner and wait for the problem to happen again (at the owner’s location)?
I suggest that you test for few more days as intermittent problems sometimes are quite hard to locate. It can be dry joints too.
Again, many thanks for having taken the time to read and answer my questions (hence, guiding me to the problem’s solution, if any).
No problem. If you have other question please do email me again. Thanks for the nice photos too!
The 2 pins with arrow light up 7 leds on my flyback tester, guessed the secondary windings having problem. Say if I savaged a transformer from some other parts by replacing at same shape and size of transformer, is this possible?
Thank you, learnt something new from you.
From the test, the transformer is good. Secondary winding rarely have problem and the problem could be in somewhere else. Transformers are uniquely designed to work on a specific SMPS and it can’t be substitutes. You have to get back the original part number.
I’d got a HCL lcd with whitescreen problem??
what are the voltage output i should check ??
Is tat a LCD panel problem??
The voltage that supply to the lcd panel. If you get 3.3 volt or 2.5 volt to the lcd controller ic then the lcd panel need to be replaced.
I forgot to tell you the voltage reading of CPU Vcc when I last mounted back the original vertical IC is 4.56V, it is indeed greater when the was no picture and only dim raster ( 4.16V ).
After using this monitor for about two days, its symptoms begin to appear ( see the attached photos ). Now, most of the time I press the menu key, only black box of the menu appears, and sometimes the horizontal black scratch appears and disappears by itself, severely occupying 3/4 of the entire display.
What clue can we draw from the above symptoms? What circuit area should I concentrate on now?
This problem can be in any circuit from power supply up till horizontal/vertical and CPU/EEPROM circuit. I suggest that you use a freezer to detect such problem. It can be an intermittent non polar cap.
Another question is the customers often ask me first for estimation of the repair cost, and that means I have to work on their monitors, but in the end after careful observation of the unit & telling the cost, the customer just refuse to repair it, saying the cost is too high. Now, the question is could I charge the customer for the observation & checking fee? Do you usually give this estimation checking fee as a free?
In fact you can charge the customer for the checking fees but usually customer would not be happy about it. That’s why in my office, we charge a standard price. This means when the customer sends in a Monitor for repair you can immediately state a price. Tell the customer if you can repair the Monitor it would be ….this price (you state your price) and if cannot repair you will return the set back to customer. The price will include the spare parts. We know that usually spare parts is not that expensive. If you found bad flyback or crt tube just return the set back to customer. With this way your customer can immediately decide if they want to repair the Monitor or not.
Thanks for the help with that LCD monitor I sow the inverter IC and I tested and got 12v dc on one of the leg it is the same voltage that is also supplied to the mother board via the connector. My problem is i have limited tools right now i have only the multimeter and to work well i need tools that can help me troubleshot problems which are sophisticated. send me a list of some of the important tools you have that help you most tell me also the company from which i con buy them.
From now on use this workshop mail address.
You need a digital capacitance meter,
a Digital multimeter,
A Blue ESR meter and
Oscilloscope is optional.
Have a good day!
How exactly to I check the backlight condition?
By comparison with a known good backlight or use a backlight tester as seen in this link:
I am repairing a Goldstar tv which has retrace lines.The vertical ic had failed and I have replaced this ic,and I have also checked the capacitors in circuit.
The television is displaying retrace lines with sound, but there is little or no video.Can you help me with this problem please?
A weak pc tube also could cause this kind of symptom. If you have check that the signals in CRT board are good then suspect a bad tube.
Dear Mr Jestine Yong,
I would like to ask you whether someone who has nothing to do with electronics can understand your e-book. Is it possible for a person like me who has no background in electronics to read and understand your e-book? Are there a lot of pictures to understand? I mean is the book in simple language so that someone who has no experience to understand partially the field?
Yes in fact i purposely write this ebook for absolute beginners. It has about 200 photos and my personal support to easily help you out. I’ve been to all the theories class and i don’t want my reader to follow my way thus i have made this ebook as simle as possible. If you have other question please do email me again.
I recall your post about finding customer and one of your service policy is about 3 months warranty.
Yes we give 3 months warranty.
As I am a newbie in this repair line, I dare only give one month warranty and here I had a problem with a customer. The monitor that I had repaired and given back to the customer had a problem again. And the customer insist that I should repair the monitor without extra fee. That is a good deal, but my question is if it still within the warranty period, but the problem of the monitor now is totally different with the first case ( f.e.: the first was CRT board problem, and now the problem is with horizontal section ), do you think this is still covered by the warranty period or we could ask for an extra fee since now the problem is different?
In my company policy we do cover the other problem too. Actually chances for a Monitor to come back within the warranty period is very slim if in the first place we do a good job by checking for dry joints, marginal e-caps, long hour burn in test and etc. Sometimes no matter what type of preventive maintenance you had applied to the Monitor, it will still come back for some other reason. As mentioned, it is quite slim.Sometimes due to competition out there we have provide some extra service for the customer. If the warranty is over then we will charge the customer.
Another question is do you have another service policy if the monitor brought in was ever repaired by another repairman. Say for example: higher repair cost, shorter warranty period, etc since we know it’s more complicated than the other bad monitor which is still intact?
We do not have this policy but we will take the chance to repair it because if we could repair it then the customer will know we are better than the other repairer thus will continue to send Monitors for us to repair. In fact we got many customers because of unsolved Monitor problems by other repairers.
How are you? My name is J. lee.
I’m fine thank you, nice to know you.
Now I am repairing lcd monitor after reading the book_LCD MONITOR REPAIR.
And I am reading another book_testing the electronic components.
Thanks for the support on my ebooks
I have some question.
In lcd monitor, is EEPROM programmed ?
Yes it is programmed
If it was so, when eeprom failed, do I replace the good one? Otherwise, do I program eeprom?
You need a programmer like the one in http://www.lancos.com to program the eeprom. EEPROM IS seldom have problem, usually is the data inside corrupted.
If I program eeprom, all eeprom in lcd monitor are the same program?
No, it is not the same. You have to get back the same eeprom data for that monitor.
For example, are programs of eeproms(24c16) in only 17″ lcd monitors compatible each other?
No it is not compatible unless the eeprom is from the same model/version
I have another question.
When powered on, lcd monitor shows display. But display soon disappears and so when I power off and on again, display shows and soon disappears.
What do I call this symptom?
Display shutdown after sometimes
What is the cause of this symptom?
Bad caps, bad inverter section, dry joints or bad high voltage transformer, bad backlight and etc.
You are welcome!
i m student of diploma associate engineer electronics 3rd year in
but i am unable to understand electronics probs because f our college
dont conduct practicticals.
i have a problem im my BENQ FP7IG+ lcd 17 inch i searched today then i
got ur site and e-mailing u with the ope that master person like u
will easily solve my problem and i will always respect u like my
problem is that my lcd shows 2 vertical lines one at left end having
green colour and other at middle of lcd having blue colour.
please answer me. .
i will wait 4
From your description, the problem is the bad LCD panel and need replacement.
In your last reply, you said: “From the photos you have sent it seems like these three caps was bit bulge. Hope that I’m not wrong. I suggest that you replace the three e-caps and retest.”.
That’s right! You have a very good and well trained eye (see “Image_12”). This simple but crucial detailed observation shows all the years of experience on the job you have. Although I had absolutely no doubt about this fact, I’m still impressed! You have been able to see this detail from an overhead view photo, while me, I have the IC board right in my face, for many days now, and I have not seen this detail before. WOW! Thanks!
You are welcome!
So, after being impressed and excited, I got a grip on my emotions and I managed to replace those three electrolytic capacitors. The three original electrolytic capacitors on the IC board was rated as 470µF – 25 volts. So, I replaced them with three brand new electrolytic capacitors rated as 470µF – 25 volts. Then, after having powered “on” the LCD monitor (with its brand new three electrolytic capacitors), MIRACLE! there is no more big “SHSSSS…” sound.
Okay, good news!
So, after the replacement of the three electrolytic capacitors, I went back to the schematic diagrams to see what are the surrounding components (upstream and downstream) of those three electrolytic capacitors (just for curiosity). While I was scrutinizing the schematic diagrams, I have been surprised to see that two of those three electrolytic capacitors that I just replaced are rated as 1000µF – 25 volts (on the schematic diagrams – see “Image_13”).
Why two electrolytic capacitors (C201 and C202) rated as 470µF – 25 volts have been installed on the IC board while the schematic diagram says 1000µF – 25 volts?
It is quite common to have some schematic diagrams that have different components value than the original board. diagram. Most probably due to some newer version of the boards but using back the same schematic diagram.
Should I replace (again) these two electrolytic capacitors (C201 and C202) by two of identical value to that of the diagram (that is 1000µF – 25 volts)?
No not necessary but you can replace it with higher voltage like 35 volts.
Talking about electrolytic capacitor, I’m maybe a little bit confused about how to test it for open circuit. Here’s how I understand it right now.
Using an analog meter, if the needle (pointer) flicks (rapidly moves to the right and then comes back to its original position – infinity) it means that the electrolytic capacitor is good. Otherwise, if the pointer stays at its original position (infinity), it means that the electrolytic capacitor is bad (has an open circuit). Am I understanding the open circuit test results correctly?
I’m asking this question because one of the six brand new electrolytic capacitors that I just bought (and rated as 470µF – 25 volts) returns an unexpected result. Using my analog meter (black probe to negative lead and red probe to positive lead), at x1, x10, and x100, the reading are as I described for good circuit (the pointer flicks). But, at x1K the pointer goes up to 0 ohm and slowly goes back to 50 ohms and stay there. Then, at x10K the pointer goes up to 0 ohm and slowly comes back to 3 ohms and stay there.
Is it all normal behaviours for a brand new (supposedly good) electrolytic capacitor or is it already starts to develop open circuit (due to the fact that on the last two tests it stays at 50 ohms and 3 ohms)?
For e-caps the best test is to use ESR meter. The reason for it is because a bad e-cap could also have a good kick and discharge back to infinity. Using analog meter to test e-caps could confuse you.
Is there a relationship between a capacitor’s voltage and/or micro-farad rating and the meter’s test position? I mean, if I take the 470µF – 25 volts electrolytic capacitor, what meter’s position is best for an open circuit test (x1, x10, x100, x1K, x10K, or any of them makes no difference and should return the same result)?
I don’t perform such test because the end result was still no accurate and you will waste your time because you will be thinking that a bad cap is actually a good cap especially when you test the e-cap with analog meter.
Also, to discharge a small electrolytic capacitors, like the 470µF – 25 volts, is a 100 watts light bulb is overkill and will it be discharged correctly?
For this small voltage of cap you can discharge it using a test pen on the two leads. But usually the charge will drained out by itself when power off.A 100 watt bulb is too big for this small cap.
Now, back to the main subject (the problematic LCD monitor). I retested the 13/15 volts start circuit’s pin and the inverter’s IC VCC pin (after the electrolytic capacitors replacement – using the same rated value as the originals, that is 470µF – 25 volts). Here’s the results.
When I powered “on” the LCD monitor, the 13/15 volts start circuit’s pin shows a 14.34 volts reading and after ±10 minutes it shows a 14.36 volts reading.
This is an acceptable value
Then, for the inverter’s IC VCC pin, when powered “on”, it shows a 14.36 volts reading and after ±10 minutes it shows a 14.37 volts reading.
Should have some tolerance-its ok
Since the voltage is supposed to be somewhere between 13 volts and 15 volts (depending on the diagram or the IC board information), is the voltage correct and stable enough in both cases or should it be showing a steady 15 volts reading (in both cases)?
It should be steady enough as long as it does not fluctuate for example the voltage value jumps to 15.5 volt then back to 13 volt and then to 14.6 volt and etc.
By the way, is there a reason why there is a 2 volts difference between the schematic diagram and the IC board label about this 13/15 volts line? Is it because the engineers could not get along on a precise voltage?
Most probably different in the Monitor version but with the same model.
In your last reply, you mentioned the possibility of a dry joint. When you say “dry joint”, do you refer to the possibility of a small (or even microscopic) gap between a component’s lead and/or the IC board’s copper track and the solder itself (see “Image_14”)?
Yes’ that’s right! It was a nice photo.
I don’t know if my understanding of a “dry joint” is correct, but here’s what I have done anyway. I gently touched and pushed back and forth each reachable component (capacitors, diodes, resistors, etc.) on the IC board, trying to reproduce the “non-conducting” state (when the solder does not touch the component’s lead and/or copper track) of a dry joint problem. But, no luck, the “power-on-with-no-display” problem still refuse to occur. Is my dry joint “search” technique is correct or is there a better way to find a dry joint?
Yes you can do that if you have the time. You can use the handle of the screw driver to gently hit the board while the monitor is running to see any changes to monitor or not. If yes, then there is dry joints or loose connection.
Right now, the LCD monitor is powered “on” for nearly 8 consecutives hours and there is absolutely no sign of the “power-on-with-no-display” problem. Like I said in my previous message, since the monitor has arrived on the work bench, it appears to work like a brand new one.
I believe it will not shutdown anymore because you have replaced the 3 bad e-caps.
So, like you suggested (in your last reply), I will leave it running for a few days again and if the “power-on-with-no-display” problem does not occur, I will return the monitor to its owner. In the meantime, is there some other tests I could run to make emerge (reproduce) the “power-on-with-no-display” problem?
You can remove the supply to the inverter IC.
Thanks for having taken the time to read this long message and answered my questions again (and again).
Yes I have downloaded your report and when I read it I was able to repair my LCD monitor, which had a lots of dry joints and a faulty capacitor
A Big thank you as I now have a spare LCD monitor incase I need one. If you have any more repair hints, please could you let me know . The monitor I repaired is a Relisys TL966 19″ it just come on for a few seconds and goes off. I did what you said in your report and The monitor now works great Thank You one again
I ordered the fluke 179, by the way.
Nice to hear that!
I am at the moment reading your ebook; ‘testing electronic components’ – very practical and straightforwardand.
Up till now I have a question to ask;
Can you explain further the difference between cold and hot ground?
Hot ground is the negative side in the primary circuit. The big fat filter capacitor in the SMPS have a negative pin and that pin is the hot ground. Cold ground is any ground in the secondary side.
And does ground replace the negative side of the circuit?
Because you have 3 wires from the mains supply, i.e. earth(ground- green/yellow) live(red/brown) and neutral (blue/black). So is hot/cold ground the earth or the neutral side of the circuit?
Hot ground is the primary side ground and cold ground is the earth ground.
I really admire you since you’re already a master in the Internet business, yet still very humble and modest to learn from others.
Learning has no end and that seminar had gave me some tips for my future Internet business plan. Just one idea, it can pay off my seminar fees.
Still repairing this monitor, I had tried to replace the video preamp IC LM1246, because I still suspected something wrong with this IC earlier when its output was very low, below 1 V. Yes, after replacing it, the moinitor was ok for about 6 hours, than the same problem came up again. To my surprise, when I had replaced the IC, when I pressed the function of the menu key, all the functions are not readable, yes it showed, but I didn’t understand each of the functions because all the symbols were meaningless ( see the photo ). Now the question is, how could we program the symbols in, if the problem were really this video preamp IC, because most of the preamp IC has built-in ROM and RAM?
During the first 6 hours did you check the OSD? Is it normal? Have you try any other function in the OSD that can choose or reset the character? Have you try another similar IC? You need the same exact part number. For example, if your IC is LM1246 then do not put in LM1246VBP and etc.
If we salvage those ICs from junk boards with its ROM already filled in, could we use it in another monitor. Will they work normally, since I think every monitor brand has its own OSD ROM?
This is consider a new type of IC as older IC do not have ROM in it. You can just salvage any video preamp ic from junk Monitor to use it without worrying about the OSD problem except this IC.
How could we erase those built-in ROM program?
Sorry, no idea about this. From the LM1246 schematic it seems that the OSD information is coming from I2C (SDA and SCL) bus line and this line source is from EEPROM. Hope that the eeprom IC data is good.
Another is about the 5 V supply, sometimes I got 4.5V, another time I got 4.2V, etc. Do you think this voltage should be the same all the time, regardless of the resolution and refresh rate?
By right it should be same. Have you check at where the source from? It seems that the 5 volt line have problem.
Have you ever found that the Blue ESR meter misjudge when testing the electrolyte capacitor? That is it shows normal ESR value, but the capacitor won’t just work normally?
Yes but very rare. That means if i suspect that the section have problem and could not locate the bad components, i will directly replace the e-caps and retest. It happened before and very rare.
Thank you for doing what you do. You are about to change my life
in ways I can only imagine. Yes I read the newsletter and ordered 2 of
the books you mentioned: Power supply troubleshooting and repair by
Lanny L. Logan and Practical electronic power supplies.
Thank you for opening my eyes and my mind to the world of SMPS.
I can’t stop reading everything you send me now.
Good day Mr. Yong, and happy new month of November 2009.
Please I have a 15″ IBM (CRT) Monitor Model G52.
The problem with the screen display is it is blurry, and tends to stress and strain the eyes. I have tried to adjust the focus nob on the Line OUT transformer, but it is still blurry.
Please as a Professional Electronics Engineer, what can you advice me to do to salvage this monitor.
Please I know you are a very busy company executive officer.
Please I will be most grateful if you can carve out time from your busy schedule and give me a clue to the solution of this problems.
Thanks in advance.
Please visit this link:
Hope ths helps!
hie can u help me with info on wht causes B+ for crt monitor jumps from nomal voltage 2 more thn 150v -220v . this voltage damages driver transitors
A bad gate signal to B+ fet can increase the B+ voltage to the flyback thus killing the HOT.
First of all thanks for your fast reply on the Anode cap remove questions.
This time I need some advise on fly back transformer.
My friend gave me a tv to repair, the problem was that while it was on , smoke came out followed by smell and
went off and NO power at All.
From this first description I suspected that it was the fly back developed a short circuit in its coil.
I opened the tv and got the board out, from a visual look there are no signs of burnt components
the fuse is ok , the HOT tested ok , so I disolderd the pins of fly back to take it out
from the circuit board to test it. to find one of the primary pins I followed the HOT collector track, till I got to the
fly back pin, and I marked it as primary pin one, now I put one probe of my digital multi meter set on continuity test on it, and started to touch the other pins. what I got were 2 readings of 0.01ohms (short) from 2 different pins!
from this I conclude there is a short is my conclusion good?
Thanks in advance for your time and effort to help me.
Not necessary as sometimes there will be an additional winding in flyback primary winding. For example, the horizontal centering winding. Unless you have the schematic then only you can confirm it.
First, let me thank you again for your immense contribution to my understanding of electronic repair. Without you (I mean, your books, your precious answers to my billions of questions, and your huge patience), I would never have been able to even execute a very simple repair task on an IC board, like replacing an e-cap, just as I did on the Samsung SyncMaster 932B+ LCD monitor’s IC board.
Now, before I officially close this e-mail thread, guess what? I have a few more questions.
If I want to use an e-cap higher than the one already installed on an IC board, should I only go with a higher voltage or a higher voltage and/or higher micro-farad?
Go for the higher voltage but not too high. For example, from 16 v to 25 v or from 25 v to 35 v and etc.
Finally, always being in the process of reading your book “LCD Monitor Repair”, I began reading the chapter “LCD Monitor Critical Voltage Test Points”. In the section “Testing the secondary output voltages” (page 116 and 117), you measure two diodes that return a reading of 5.14 volts and 13.68 volts respectively. My question is the following: If I execute this same voltage test, how am I suppose to know if each diodes that I test return the right voltage? Is it because the voltage that you use in your example is static (I mean, the return value is always ±5.14 volts and ±13.68 volts for any secondary output diodes)?
That voltage measurement was just a rough guide on how you can perform voltage test. The voltage value is not important because different model have different voltages.
Is it depends on the output voltage from the primary side?
The voltage that i got was depends on the total number of turns in secondary winding of transformer. The higher the turns the higher is the voltage.
Is any voltage higher than 0 volt is correct? Or, well, as you can see, I miss some probably basic information here about the secondary output diodes voltage test results. Please, enlighten my lantern.
It depends on which output line you are referring to. For example, a heater line of a CRT monitor have to be 6.3 volt and if you get 2 or 3 volts then you know that the line have problem. Similarly, if the MCU of LCD Monitor need 3.3 volt to run and you get 1 volt then that line may have problem or the MCU itself shorted that had pulled down the voltage.
However, I think that I learned a very basic and crucial concept in this chapter; that is: Always use HOT ground when doing voltage test on the primary side and always use COLD ground when doing voltage test on the secondary side. Is it correct?
You are right!
Thanks for having taken the time to read and answer this unusual short message (compared to the previous ones) with no images (I hope that you are not too disappointed).
No problem. If you still have other question you may email me again.
Thank you for the Email,
Always like reading them.
I wonder if I may ask you a question,
I have a Hansol Model name H950, Model number B19BF.
When you turn on this monitor it takes about 15 min for it finally will come
on, I have to turn the power on and off several times to get it to light up
after it is
Once on and running it stays on all day as long it does not go into sleep
mode for any
length of time, than you start all over again.
I have been trying to get the back off but nearly impossible.
Would you have any suggestions? or should I scrap it.
It is at least 5 years old, as I said, once on it is beautiful 19″ screen.
Thank you for your time.
Check on the heater voltage and it should have about 6.3 volt dc and if the voltage is present then suspect a bad pc tube. hope this helps!
i have a question JESTINE
how can you find out if lets say the lcd screen
from ltv LTV32W6 or LTV32W2 (westinghouse lcds)
will fit polaroid FLM3201 or FLM3232 lcds
is there a cross reference site or book
i believe these are made by same company
Actually there is no or hard to find such information. I guess you may need to test it out to see the result.
I want to learn how to read,follow & understand circuit circuit diagrams.
How components on a circuit interact with each other & how they work.
What each different component does.
How to design circuits.
if you can help me, guide me i would be very gratefull
The best is to get the basic electronics book by bernard grob as it has all the answer. Please visit this website too :