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Electronic Repair Questions/Answers & Testimonials Part 4

By Jestine Yong on June 27, 2008

“i had discovered that this monitor has 2 horizontal output stages on for driving the horizontal deflection yoke and one for driving the high voltage when i removed the horizontal output transistor that is driving the horizontal yoke the monitor works ok but it has only one vertical line wowwwwwwww yepeeee……..this prove that all circuits are working only the defective one is the horizontal deflection output we have good smps good vertical good high voltage good color stage good crt ….so now with this horizontal transistor removed i test the b+ and i find it 180 volt this is seems to high ???”or it depends on model??

May be yes (it depends on model). the best is still get the measurement from the anode and it should have about 24 to 26kv.

is it high because it is unloaded or it is high because it is defective? You need to check the output from the anode first before make any conclusion. so why when we connect the transistor to the circuit of the monitor and power it up why the high voltage work then shutdown we know that it is not related to the high voltage it is just horizontal transistor for the deflection ..what do you think the failure is?There could be many resons i just have to repair and check it out if i come across one. One thing for sure is that i want to see how high the high voltage goes before it shutdown using the high voltage probe. If the high voltage shutdown at normal high voltage then it could also mean that the crt tube breakdown when under full load. If it shutdown due to extreme high voltage then you got to check the B+ voltage, safety caps, internal cap of flyback again.————————————————————————————

I repair all type monitor but one problem is not solve of the EHT related , monitor Display is dim & screen is not clear i check the all monitor spar his OK only create the problem in the EHT so you pl adv me,
1)How to solve the problem ?
It could be picture tube bad or the heater voltage not enough to the picture tube.

2)How to match the EHT ?
You have to use back the original flyback3)How to Check the EHT?
Use a flyback tester and visit this page http://www.electronicrepairguide.com/testing-flyback-transformer.html—————————————————————————————-Hi Jestine,
The guide that you give to me about my tv problem is correct.I’ve resoldered all p/supply surrounding area and finally the result is satisfactory.Thanks a lot about the info especially about the transistor.

Farizal

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Hi Jestine,

It’s quite some time I have not ask you some questions.
What is the common fault in a dell lcd monitor?
My dell 1704FPTt which I have been using for a few years now give problem.
Display missing after using 1 hour. It do not go into standby mode when display missing. If you off power and on back, display comes back for a few seconds only. The front led light remains green.
Can you help to give me solution?
Thank you.

Hi A,
Dell lcd monitors have a common fault of dry joints in the high voltage transformer. Just direct resolder the transformer as some of the joints looks okay. Then you can retest the monitor again.

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Hi Jestine,

I have a rear-projection TV with a high-voltage output transistor NPN type 2SD1885. Does the book cover how to test this transistor in-circuit with the power on ?
No, i only cover in circuit test with power off. I even cover how to test this transistor off circuit too. This is a horizontal output transistor (HOT) and used in CRT Monitor and TV’s. There is no need to power on to test this transistor because if the flyback transformer already working you are 100% sure this transistor is working.

I have read some information that says this transistor is the most stressed component in this TV (RCA P46720BALG2).Yes, all HOT are stressed components because of the high voltage switching and i have replaced lots of HOT during my 17 years in CRT Monitor repair.

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Hi B,

For the mosfet cross reference data sheet, one of your article says: “one has to look for a semiconductor transistor replacement data book and not the Philip ECG master replacement guide. What are the components that the Philip ECG doesn’t cover?

Since there is no update in Philip ECG (the last version printed in 1998) anymore, we could not get any latest spec from lots of the components. It covers many components and many of it was not complete.

What is the name of the book of mosfet cross reference?

They have volume 1 and 2 and it covers lots of components like fet, bipolar transistor, triac,scr, diode, zener diode and etc. I’m at home now and forgot about the name but it is something like ” Up to date World’s transistor, diode, thyristor and ic”

One of my friend is in Singapore now, and I hope he could help me to buy some books. Do you know where to buy that kind of books in Singapore? In parts supplier or in general bookshops?

Get your friend to go to sim lim tower look for tech publication at the ground floor

Also could you name a few of the electronics book about the buck and boost circuit operation or tutorial for me to familiarize with them?

Internet have lots of explanation about these circuits.

Another article about CRT monitor color problem, if the EEprom data is corrupted, the only way is to reprogram the IC or use a soft jig to tune it back. What is a soft jig?

It is a sofware plus some tools to plug into computer and the monitor for communication. The sofware will adjust whatever setting in the monitor.

Also I am interested to have a demagnetizer, is it easy to built one myself, do you have the circuit diagram?

Sorry i don’t have i information about this demagnetizer. It is quite cheap and your friend can easily get one from singaopre too.

When I search posistor in farnell why the posistor has only two legs? What are the difference between posistor having 2 and 3 legs?

Both actually is the same, is just that the manufacturers preference of selecting on which type they want to use in their design.

Why I couldn’t find monitor blur buster in all the parts supplier? Is it a product that you develop by yourself?

The part was from other country and we imported and sell it in my country.

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Hi Robin,
Thanks for your good testimony! Here is your questions:

My question

this thermal shutdown circuit does it shutdown the ic when it’s 2 hot and when it’s cooled down it restarts the ic
or is the ic lost after shutdown?

Yes, whenever the ic gets too hot it will shutdown and you need to wait for it to cool off before you can restart/on the power again. It would not damage the IC.

This thermal shutdown just like our dot matrix printer head where arfer using for many hours without break the printer will stop itself to let if cool down. Once the temperature gets back to normal it can resume printing again.

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Hi Jestine,

My cousin has a subhoover and doesn’t work anymore…
The secondary windings are damaged and cannot be tested.

i noticed that there are 3 wires in the output side with two blues colors
and 1 black color. while on the board the black color connects to the ground
and the two others are connected to the circuit.
The specification are as follow:
Size: 1050 (66X28)
InputAC: 220V 20070302
OutputAC: 18VX2

My question is: i have a similar rated transformer with only 2 blues wires
on the output side (without the black one).
when i connect the 2 blue cables from the transformer to the 2 blues cables
on the board there a strange sound comes up while the light is on to show
that the power is flowing in. and when i connect 1 of the blue cable to the
black which is the ground and the other in the blue one the device is turned
on but no sound at all.can you please help me sort out this issue?

Thanks for your help
Hi H,

First the original transformer have two outputs which is 18V X 2 and the black is the reference ground. In your replacement transformer you got only one output which is 18v and the ground wire. You need to have a transformer that have two outputs for it to function and of course the ampere must be the same or higher. You could also power up two similar transformer to get two 18V outputs but the cost would be higher and also the space problem to install the transformers.

Jestine

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First the original transformer have two outputs which is 18V X 2 and the black is the reference ground. When you said 18VX2, it means a total of 36V? .

I believe it is a separate winding. That’s mean two outputs

You need to have a transformer that have two outputs for it to function and of course the ampere must be the same or higher When you said higher, what is the maximum? (because to higher may cause damage) .

Lets say the original is 4 amp you can install a 5 or 6 amp transformer. Any higher amp would be a waste in term of cost.

You could also power up two similar transformer to get two 18V outputs but the cost would be higher and also the space problem to install the transformers.Here you mean i can use two 18V transformer…but how can i connect them (in parallel or serie?).

First transformer have two wire-one to 18v and the other to ground. The second transformer also with the same configuration

Can i found a 36V (output) to install it instead of using two of 18V?

No you can’t because it is two separate windings.

Is there any way i can modify this 18v to 18X2? (its just a silly question).

I’m afraid the transformer will overload.

by the way, thanks alot for your help and assistance and hope to have your reply very soon.

You are welcome!

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I have a ERG member who told me that he repair electrical and electronic equipment. I sent an email to him asked about what kind of electrical and electronic equipment he was repairing. This is the answer that i got from him:

GPS, GSM & RF Module install in vehicle for recovery and tracking system, RF receiver Unit for receiving RF signal from vehicle that was install with the RF system, Groundpack that can receive RF signal and send MRA (medium range activation) to enable the vehicle brake light (blinking mode when enable & enable the fuel cut (to activate the fuel cut which will off the fuel pump system in the vehicle that was stolen) unit use for tracking vehicle that was install with the RF system which was stolen, Airpack also use for tracking the vehicle when was stolen but this module use in the Air (chopper). Airpack can receive RF signal, send MRA & also LRA (long range activation signal – to enable the the brake light (blinking mode to informed the recovery team and also identified then when the road is clear the recovery team will send the fuel cut signal which will gradually stop the fuel pump which will stop the vehicle from moving.

Wow! He is in this kind of repair field which is totally different from mine. This kind of repair line needs many special test equipment for test and alignment purposes. All the best to him!

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i need u r help regarding selection of MOSFET

for dc dc converter application,

which is smps based 390v dc to 54 dc, 100KHZ switching, in which manufacturer using IXFH20N60, that is not available in market,and too much high price, thats y i need alternate discreet mosfet to replace, i also tested by using IRFP460,And igbt f25n120 but temp getting high, may coz of high switching frequency, please suggest me any mosfet r igbt which is low in price.

Hi D,
Sorry, i don’t have any information about the pricing. Try check the list of the electronic suppliers from my blog at :https://www.jestineyong.com/?cat=12

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I have a power supply for a packard bell LCD TV1) MBR20150CT faulty

2) 20N60C3 faulty

I found that the transformer top lead go to GND

the other pins from the transformer GO to MBR20150CT one half side of the MBR20150CT was faulty.

The Secondary side of transformer has open circuit put meter to GND and all PINS from transformer has very low reading that is 000 on the meter

Remover top lead from transformer test it ok put back top lead get 000 on meter

It hard to get the transformer for packard bell

the transformer is LT281P0001 HJC 0416Q

Hi W,
Since secondary winding have less turns if you test it with an ohmmeter it may show zero ohm. If one of the diode shorted in MBR20150CT you can actually try to disable the shorted diode pin and replace an external good ultra fast recovery diode as replacement. Try the diode number UF5404. As for the packard bell transformer, yes it is quite hard to get the part. If the Tv have two similar transformer you can actually compare the reading with the flyback tester and the ohm meter. Hope this helps!
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Dear Jestine,

How are you and sundries over there? Hope all is fine.

With all respect, may I use this medium to seek your expertise advice on a problem I had with one of the Pentium iii Dell SMART PC I00N laptops; I have on my repair table.

This laptop boots but doses not illuminate the screen. At times, I notice some object display but no light on the screen. I have tried using another external monitor and still of no avail. As of this hour, Iʼm suspecting the VGA card but in the absence of the VGA, what could be the problem and how can I solve this problem.

Thanks and ever remain blessed as Iʼm waiting; hoping to here from you.

ENGR IKENNA.

Hi Ikenna,

Yes, it could be the VGA card problem or the inverter fault. Try use a torch light to closely see if the image is there or not. If it is there then the inverter board may have problem. If there is no image at all then suspect a bad VGA card. Hope this helps!

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Hi Martin.
This SMPS hasn’t preset on it.

Then the designer has used a resistor to fixed the value.

If there is no 18Volt then I should start to trace back to see at where the voltage has missing, all this in the power supply??

Generally Yes and see at where the 18v comes from

So for the big experience you have, do you think the problem (satellite receiver doesn’t turn on) could be an electrolitic capacitor?????; actually the 12V regulator on the secondary side gets very hot

A fail e-cap could cause the voltage regulator to run hotter than it should be.

Thank you very much for your advice; I’m gonna get one ESR meter, by the way the one you sell is already assembled and calibrated?????

Usually it is in the kitform, if customer wants to buy the fully assembled kitset then only i will install the kitset and calibrate it. At the moment i only left one unit but the new shipment will be arrived in another week. The demand from my country and oversea order were quite good.

I’m gonna send you an schematic diagram I found on the net for this smps, it’s not the same with some components on the primary side, but basically the same on the secondary side.

Wow! that would be good!

I hope you have a nice day.

Same to you!

Best Regards,
Jestine Yong

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Jestine,

My name is Mike I have a small home business doing PC and electronic repair. I was a technician for a computer company for 20 years and went to school for electronics. I am currently working in the networking field. I am working on a BOSE system for a customer that was damaged in a thunder storm. It is blowing the main 3 amp fuse whenever the unit is connected to 115 AC. I have found and replaced three shorted TDA 7294 audio output IC’s but the unit still blows the fuse when plugged into the wall. I removed the main transformer and put it on my Sencore LC103 unit and tested the windings. Most of the winding will ring with 4 or 5 rings but the primary winding will only give one ring and gets a reading around 46 uh. most of the other winding read around 118 mh. I have tested many fly-backs and know what they should read, but this is the first time I tried to test a power transformer. Do you have any suggestions ?

Thanks,

Mike

Hi Mike,
Nice to know about your background in electronics. In your case it seems like the transformer have problem. I once had similar experience with an Acer CRT 14″ Monitor and the set blow the fuse every time i “on” it. It turned out to be a bad primary winding after tested it with dick smith flyback tester. A good one should have about 5 bar LED but the bad transformer have only one LED! Why not make this test to confirm it. Remove the fuse and connect a 100 watt light bulb across THE FUSE HOLDER. A shorted primary winding will cause the bulb to light and won’t go off. On it for couple of minutes and then off the set and quickly discharge the filter cap then use your finger or hand to touch on the transformer. If the transformer is extremely hot then you have found the fault. Hope this helps!

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Hi Sam,

When is your SMPS book due out ?

I’m afraid not so soon due to lots of repair courses “On” nowadays. Next week have another class, after the class i would be very tired and need some rest. I have completed only 65% of the book. It may be in the physical book and no more ebook. I haven’t decide it yet.

I have been working mainly on LCD TV’s this past 12 months and I could have used some help. Is it possible to get a table of contents of this book ?

Sorry Sam, the contents is not final yet as i will add on more tips in it.

In your book, do you cover how to trace and measure the high voltage, high frequency current in SMPS secondary ?

I only cover the voltage testing. May i know why need to measure the high frequency? If all the output voltages are within range with load then i consider it as good. If you have tips about this high frequency could you briefly share-thanks! In my LCD Monitor ebook, i use the frequency meter to confirm whether the high voltage transformer is working or not by placing the probe on top of the transformer.

Large LCD TV’s have as many as 20 CCFL’s which makes it hard to figure out which circuit is causing the shut down. Attached is a photo of a Sharp Aquos 32″ with 12 CCFL’s drawing current from 4 transformers. In this case the problem only manifests itself after the TV is sufficiently warmed up (1 to 3 hours) and the only quick way to weed out the marginal components is to trace each live inverter circuit. How can I do this without an oscilloscope or spectrum analyzer ?

I’ve never repair any lcd tv thus i can’t give any specific answer to you. Anyway you can try out to measure the feedback circuit voltage. It should be constant. If the light is inconsistent it will send a feedback signal through the feedback circuit and cause the lcd to shutdown. Monitor each of the feedback signal and if the one have some changes then that’s the bad backlight.

My Craftsman multimeter has a 0.001Hz to 10MHz range and I have used it to trace the SMPS flow in 23″ and smaller computer monitors. The probes would pick up the electromagnetic wave if I hold them close (without touching each other or the board) to the live circuit. LCD TV’s have too many inverters close to each other for this method to work.

If too close you will only get the same reading, try the method above.

Finally I’ll like to add I enjoy your monthly newsletter very much, Thanks for sharing your expertise with all ERG members.

You are welcome and in fact now i’m writing the august repair newsletter and due to be send out on saturday evening. By the way sometimes i wish that i have customers send me lcd tv for repair so that i would come out another ebook about lcd tv repair (practical guide).

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Hi B,
I own ACER AL1706 17inch LCD monitor, I have used the method described in www.fastrepairguide.com to login to factory service mode, that is before “ON”, press and hold the Auto and Menu button first, then press the power button. But the display could not on, what I could see is only the power button is blinking with amber color. The monitor has no problem and I just want to enter the factory service mode. What could be the problem? Is there any other method?

Different LCD model have different setting but because your model is different from the fastrepairguide lcd model, you may not enter into the factory mode. You have to play around with the button combination until you could get in. Many times it would be difficuly unless you have been told by the authorized service center on how to go into factory mode.

Do you often use thermometer function in digital multimeter. Do you think it is necessary to have a meter with this function?

I don’t use this function. However you may use it to check if the replacement components getting hotter or not. If yes, then the replacement components would not last.

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Hello there- Thank you for your informative articles. I must say I am enjoying them. I have a little problem and hope you can lend some advice based on your experience. I repair equipment for a local outlet store and one item is DVD players that are returned by customers for problems. I noticed that one very common problem with this model is the fact that SMD components get loose on the board. There are so many of them and, as you know, they are very small. Besides, I don’t know exactly which parts are the problem. I say this because when I flex the board in that specific location, the unit works fine (as long as I’m keeping pressure). Clearly, this is a sign of bad connections. But I don’t know how to REFLOW solder in tha area or fix the connections. These are very delicate parts and if I don’t use the correct procedure I can potentially do more damage. What would you do ? Many thanks.

Bill
USA

Hi Bill,
Just use the rework station and do the reflow at the solder points. Set the air power to the lowest and temperature about 450 celcius. Rememeber to apply some soldering paste too. Reflow one component at a time and hope it could get rid of the dry joints. Have a nice day!

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Hi Jestine,

Why do you like electronic?

Satisfaction in solving problem and curious about seeing all the tiny components could form so many different types of circuits.

How many years do you have to spend to become a real electronic repairer.

If you focus on one or two electronic equipment and have the equipment comes in for repair i guess it may takes only couples of month to specialize it. Of course during the few months time you got to do lots of homework like reading, practice, analyzing schematic and etc.

Sometimes, it is far easy to buy than repair the t.v.

You are right but if you could repair it the knowledge will stick with you-perhaps forever (due to hands on practice!)

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Hanns-G 17″ Widescreen HW173D LCD monitor got wet. Power LED is on but flickers intermittently, no picture when connected to computer. Any suggestions would be greatly appreciated.

Hi D,

The flicker could be cause by components failure in the primary or secondary or both section. It caouls be also a failure in the mainboard. First dry up whatever water in it and start to check the voltage outputs at the secondary side. If the outputs are okay suspect a bad mainboard. If the voltage fluctuate then check all of the components in the primary side. Hope this helps!

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Good day Jestine,

You probably had already forgotten me, let me refresh your memory… if you still remember a guy who managed to repaired his 19″ Philips 190S LCD monitor after purchased and read your ebook? That’s me. 😀

Previouly, the FET power transistor (SSS7N60B) was faulty and once I replaced it, the LCD monitor back to its live. This lasted for about 6 months and again it could not be power on, so I went ahead and replaced the same FET power transistor and of course its back to live after that. 2 months later, the same problem re-occured, replacing the same FET will back to normal for some months.

Please advise me what can went wrong and how should I focus on to find out the caused of this? Should I find a substitute transistor that with higher spec. or there should be some other component is faulty so as to cause the power transistor shorted after sometime?

Thanks in advance.

Hi W,
Yes definitely i remember you! In your case there are few possiblility. First it could be a non original components, second the heat sink compound could be not enough, third-design problem (too hot and etc) and fourth corresponding components have problem.

Few possible solution:

Increase the size of the heatsink,
Place more of the heat compound
Direct replace the current sense resistor (usually 0.22 or 0.33 ohm) and also the e-caps.
Replace with a bigger amp fet with the same ohms rating and
place a two small bead across the gate and the source of the FET to remove any interference that can cause the FET TO BLOW.

Hope this helps!

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Hi Tutan,
Thanks for your support on my ebook.

“I have a question: i started to repair a LCD Monitor Sony SDM-HS73, if i not plug the vga connector the bl_on voltage are active but the screen remain black(lamp switch on for only half second), if i connect the vga cable whit signal, the bl_on voltage random from 0.11v to 3.80v(if voltage is 3.80v the lamp switch on, else is off), in 1 minute the lamp switch on for max 2 or 3 time max for 1 second. I have measured on inverter ic, vcc in and output and all signal are good if not connect vga signal, if connect vga signal, vcc voltage for inverter IC are not stable(vcc arrive from bl_on?), please if you have any idea help me to find a solution, unfortunatly is possible defect MCU unit?”

I have came across this problem but not in Sony, it was in Samsung 510N Monitor. The cause of the problem was the MCU and since i do not have the programmer at the moment, i direct replace the mainboard and it worked perfectly okay.

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4 Comments

nowdaygood

June 28, 2008 at 1:26 am

Dear jestine
Can you give me some Fujitsu LCD monitor schematic.
Best forum
bye.

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admin

June 29, 2008 at 9:15 pm

Hi,
Sorry i do not carry schematic diagram. Try http://www.eserviceinfo.com. They also have a forum in the website.

Jestine

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Samee

February 4, 2012 at 11:53 am

hi Jestin, I need your help. my samsung 793mb monitor not turning ON. few days back was wrkong fine but there was some flicker on screen, by adjusting base plate I was able to resolve that issue but unfortunately one day it stopped working while it was On. now there is some tickling sound out of it, not powering On at all. I have taken out thecircuot board n visited on Tv repair shop. as per hom EHT must have damaged, but he is not sure. I brought back but not understand what should I do? is EHT same as FBT? its FBT numb is T501. help pls...

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admin

February 5, 2012 at 3:50 pm

HI Samee,
EHT is the same as FBT. First you need to make sure the power supply is giving good output voltages. Is there B+ 110v to the fbt?

Jestine

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