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Electronics Repair Questions/Answers and Testimonials- Part 82

By Jestine Yong on July 6, 2011

Your e-books have been a great help for me ,,,,,Actually I also attended the training institute before but not much learning ….Your’s have beaten those ……trainings ….. Thanks again….

Karna
Nepal

==========================
Hi Jestine.

I am about to purchase your Ebook. My true confession is that, I have always wanted to learn Electronics Repairs but I was surrounded by a lot of "selfish" individuals who never share their information. Thank God for people like you and the "Internet", I am now able to do my online research.

Please continue to send me these articles.

Bradley (Newbie)

========================

Through your repairing electronics course,, I was able to test and FIX a TV that cost me $3.50 in parts and would have cost me $200.00 for A new SMPS. The AKAI 4294 I found the 2 bad capacitors that did NOT look like normal capacitors and did NOT test like capacitors since they were still soldered in the main board, (C 523 and 524,, NOT the C 524 and 525,,,,,C525 does not exist on that board!)) Once I removed them,, I found the problem. The TV came on right away.

Ben

=====================
HI Boling,

The owner had asked for the set but I’m still have some questions about it. Sorry, don’t have the opportunity to compare the resistance of both circuit anymore.

This monitor is using the FP5451 Dual Channel PWM Control IC with two output. From your experience, the output of both channel of a Dual Channel PWM IC should have the same waveform or not.

By right should be the same.

Here I attach the application note of this FP5451 IC, and the circuit is similar to the set I was working on, in that they are using two pcs of 9435 Power- Trench. Before I took out the inductor, one 9435 output is 5V, the other is 0V. What could be causing this, do you think? How could the IC produce different output voltage, what is the key component to produce different output voltage, since this circuit seems to be symmetrical?

If both 9435 should produce 5 volt but only one that had 5 volt then this mean that particular 9435 or surrounding components have problem since you have mentioned that both also have good output waveform from FP5451 IC. Comparing the resistance is the fastest way to tell since both have similar circuits.

How could the IC produce different output voltage, what is the key component to produce different output voltage, since this circuit seems to be symmetrical?

By right both should produce the same output but because there might be bad component/s in the corresponding circuit thus you get 0 volt. Assuming both have the same circuit design, it is the pulse of the waveform from the IC that determine the voltage.

Jestine

=========================

Hi B,

I was referred to your book by Dave at Grants pass Oregon TV repair. I WILL be buying it soon.

Noted.

I am a newbie in the TV repair field however I have a lot or knowledge doing car stereo and automotive electronics.
I have just acquired an electronics repair business inventory including all the test equipment such as older sencore cap/induction analyzer,,An EDS Capanalyzer,An analogue Oscilloscope, Audio sweep Generator, Frequency counter,, 2 Tube testers, An Isolated adjustable power supply,(kind of like a Variac but nicer), A universal video analyzer, FM alignment generator,, A distortion measurement system, I think I even found a FLUX Capacitor generator,,,,It’s what makes time travel possible,,Hah,, And on and on.
I have found out how to use some of this stuff and am learning what some of the other items are for. I have only had this stuff for about 3 weeks now.
I also got well over 15 flat screens in various states of repair or had parts robbed out of them,, filing cabinets,, phone systems,,mini digital video cameras, 4 projection type TV’s,, many tube type tv’s,,, on and on and on.
I am now in the process of learning how to repair the 6 or 7 that still have all their parts and am looking for new screens for 3 of them that are cracked.

Since the car electronics business is a thing of the past mostly,, I need to find work,, and since I got REALLY REALLY lucky getting all this stuff for 400 dollars,, I am going to do my best to make a living doing this if I can.

If there is a will there will be a way-just don’t give up.

Right now I am working on an AKAI PDP 4294 Plasma TV and I do not have the schematics,,( I am still learning to read schematics), I could just buy new boards but that would be expensive, but mostly I wouldn’t LEARN anything.
I have tested the voltages coming out of the power supply on it (it’s a fairly large PS board) and compared them to the sticker as to what they should be.
I am getting mostly OVER voltages and they don’t change when I disconnect the other X or Y board attached to it.

The VE is 230V and should be 107V, The VS is 58 and should read 87V, The VA is 176 and should be 79V, The VSET is 208 and should be 93, and the VSCAN is 174 and should be 78V. Even the D5V is reading 10.7V
Where should I look next? I am sure that I am missing something.
There are no bad caps that I can find,,Fuses are all good,, even the surface mounted ones,NO bad solder joints, nothing is burnt,, smells bad or is visibly corrupted.
Thank you for any help and please let me know If I am bugging you too much.

I’m not sure about this model but a failure in the feedback circuit in the power supply board could cause all the output voltages to increase. Pay special attention to components that is nearby the optoisolator ic especially resistors.

Jestine

=========================

Good morning Jestine,

am glad at informing you that i have received the june repair newsletter.Thanks a lot for that.however i have got a problem on my AIWA compact system.the precision resistors have broken down and there are not readily available in the shops.is it possible for me to use normal 10K resistors so that the system can come back to life?i await your feedback.gud day.

Langstain.

HI Stain,

Try use wire wound resistor instead of carbon film because precision resistor usually is designed to withstand high surge current.

Jestine

=======================

hi jestine
i have a problem with monitor hp 1530 when switched on it goes on a bit bright then faint that is characters are seen in side.
please help
peter

HI Peter,
Check for bulged cap and make sure the output voltages are good and stable.

Jestine

======================

HI Patrick,

congrats with the new website.

Thanks!

I have bought three of your ebooks and are learning alot.

Thanks for the support!

After reading them and tinkering a bit, I have some questions I hope you
can help me with.

For a repair I am doing now:

1) I have attatched a picture of a cap. It reads 94pF. Is this correct
for this? I have a little problem reading out the value and type. Is it
a standard cap?

it may not be a cap. it could be a varistor. What is the board marking of the component? Is it "C" or Z ?

2) I one spot there are a component that the PCB mark as F1. That is a
fuse. It has the size and looks of a 1/4W resistor, and are marked Green
Black Silver Gold in the rings. As far as I can see this reads like a
resistor 0.50 ohm 1%. Can a resistor like this be a fuse? (It is in one
of theese lamps with a 240V AC straight up, and a 12V AC on a
gooseneck).

Yes this resistor act as a protection resistor and will open circuit if there is a short circuit.

3) About the diac’s. I will replace two DB3 diac. Is there any polarity
on diac’s, or can they be soldered on both ways?

No polarity and you can solder it either way.

And a couple of general questions:

4) Resistors:
For service/repair purpose, is there any reason to stock up on
carbonfilmresistors (1/4 W) instead of metalfilm resistors (0,6 W)?

It depends on the type of board you repair. The best is to replace with the exact type of resistor.

OK, the price it somewhat higher (but not much where I shop in my
country) but for a handfull or two of each value the cost difference is
insignificant.

The size is the same, about 6,4×2,3 mm.
The tolerance is better for metalfilm, 1% instead of 5%.
The powerrating is higher 0,6W against 0,25W.
The metalfilm can be used in RF circuits (as I understand it).

As I understand it the metalfilmresistors can be used i many more places
during service/repair as it holds 1% and 0,6W.

Is there any reason not to use the 0,6W metalfilm to replace the 1/4W,
1/8W (if size fits) etc carbonfilm? Just want to know so I do not
destroy anything!

To be honest i did not use metal film as replacement because carbon film

1) is cheaper to get from the market

2) is easily available in all electronics store.

3) usually i like to use original parts unless i really could not source the original part.

If you do not mind about the price, yes you can go ahead to use it-no problem.

5) Diodes:
About the 1N4001 to 1N4007 series diodes.
Is there any problems if one replaces a 1N4001 (50V) with a
1N4007(1000V)? They have all the same Amp rating. The only difference
is as I read the datasheet the voltage.

No problem. I used to do that since both of the diode price is the same.

The component stock will be much more simpel with only the 1N4007.

You are right. My component compartment only have the 1N4007.

Will I run into problems if I replace a 1N4001….1N4006 with a 1N4007?

No problem.

6) Diodes:
And the same with the series 1N5400 thru 1N5408. They are all 3 Amps but
have different Voltage rating. Will 1N5408 (1000V) do as substitute for
all of the others 1N54XX?

Yes 1N5408 can be used to substitute to all the 1N540X series.

Jestine
http://www.BestElectronicArticles.com

================================

HI Victor,

THANKS MR JESTINE, THE METERS ARE IN MY HANDS. IT ARRIVED THIS EVENING.

I DONT KNOW HOW TO EXPRESS MY JOY. WHEN I SAW THE FEDEX MAIL RUNNER STOPPING INFRONT OF MY OFFICE AND LOOKING STRAIGHT AT ME AS IF HE WANTED TO ASK ME A QUESTION I HURRIEDLY ASKED HIM IF HE WAS COMIING TO MY OFFICE AND HE SAID YES.

I HAVE ALREADY FIXED THE BATTERY AND THEY ARE READY TO START WORK IN THE MORNING.

Good to hear that.

PLS WHAT IS THE USE OF THE 2 RESISTOR

For calibration purposes. You do not need it because i have calibrated for you.

AND SOMETHING THAT LOOKS LIKE A COPPER WIRE THAT IS IN THE CARTON OF THOSE METERS. ARE THEY SPARE PART ?

The wire and the core is for you to loop and test by the meter to see if all the LED in the blue ring tester lighted or not.

Have a good day!

Jestine

=========================

Hi jestine,

My lcd screen is showing scrambled, the sound is fine. I have gotten
someone from a reputable firm to check it but after a week of showing really
well it went back being scrambled. Please help!

Laura

Hi Laura,

The problem could be lcd panel or the internal cable that have loosen between the mainboard and the lcd controller board.

Jestine

========================

Hi Jestine,

thank you for your swift reply.
For a repair I am doing now:

1) I have attatched a picture of a cap. It reads 94pF. Is this correct
for this? I have a little problem reading out the value and type. Is it
a standard cap?

it may not be a cap. it could be a varistor. What is the board marking of the component? Is it "C" or Z

You are of course right. I have now got out my magnifier and dusted of the whole PCB, and the marking are indeed a Z for a varistor.

I have checked it as outlined in your testing-book and there are no needle movement at x10K, so it is OK.

Pretty funny that it fooled me by reading 94 pF when checking it first time with the multimeter. A real learning experience.

Thanks for your help.

Best regards

Patrick

======================

PLS SIR AM STILL HAVING SOME CHALLENGES WHICH I KNOW WILL BE OVER SOON. THE BLUE ESR METER READING SHOWS FIGURES THAT ARE NOT ON THE CAPACITOR. HOW DO I KNOW THAT A PARTICULAR CAPACITOR IS GOOD.

HI Victor,

The chart is for your reference and the value that you get should be lower than the chart. If the value is higher than the chart then you need to replace the capacitor. Try test more of the capacitors and you should be good at using it. Remember to initialize the meter first before testing. Turn the meter on, short the probes and press the button again to make the display to become "OO". Now you can start to check the cap.

Jestine

=========================

Hi Lito,

I have already printed SMPS e-book and to date i’m reading a lot. I wasn’t able mistaken to buy your book, i have a lot of books since my college days but unfortunately your e-book is unparalleled. Your E-book is just a library. I have installed my small electronic shop and with the help pf your book i easily isolate the problem of epson printer and back to life. Thank you again sir.

Congratulation! And you can use all the repair techniques to repair all kind of SMPS.

Further, my plan is to buy your best articles e-book and the LCD repair book in the next few weeks.

Thanks for the support again.

Jestine

============================

HI Noorishkandar,

Sekiranya LCD screen rosak dimana saya boleh membeli alatgantinya?Any suggestion?

Biasanya susah untuk cari pengganti. Bagi saya, sekiranya screen rosak saya akan cari kat junk monitor ataupun beli dgn harga murah dari pelanggan tersebut untuk ambil part lain seperti power/inverter board, mainboard, backlight dan sebagainya. Untuk repairer kat USA mereka beli dari ebay.

2.Saya sedang troubleshoot sebuah Laptop Compaq CQ40.Masalahnya NO Display tapi bila switch on power ada.Any tips from you to solve this problem?

Dah connect ke external monitor? kalau masih tiada gambar kemungkinan Display chip dah rosak. Kalau ada gambar, inverter ataupun screen dah rosak.

Jestine

============================

Hi Justine,
I am working on an LG (Model: 42PC7RVH-TA) and found that a transistor in
the power supply is blown. The number is "K4014" and no one in South Africa
has it listed.
What can I use as a replacement?

Regards
Wayne

HI Wayne,

Sorry i could not find the replacement for you but there is a website selling it:

http://parts.digikey.com/1/parts/1690868-mosfet-n-ch-900v-6a-sc-67-2sk4014-q.html

If you insist to test on the replacement, you may have to take the risk-try 2SK2645.

Jestine

==========================

HI Douglas,

I have found a bad resistor in my LCD Switching Power Supply. It does not look like a typical resistor, but it has 1.2 OHM stamped on it. I noticed a small smudge on the circuit board and upon checking with a magnifying glass I noticed the blown out section on the body of the component. It checks open with an ohm meter and I have assumed it is bad. Since it has no color code on it (its tan colored and looks like its coated in ceramic), I am not sure if it is a common resistor or not. In your book there is the section on Thermistors and Varistors, but this component is located after the 1st bridge rectirier and there are 4 of them on my board, so due to the number of them and the location in my circuit I don’t believe it is a MOV. I had sent this message through your email address and attached photos, but that email came back unable to deliver address not good problem.

Usually if a component marked as 1.2 Ohm then it is a resistor. If the component board location is "R" then it is indeed a resistor. You can send to me the photo at jestineycs(at)yahoo.com for me to confirm what kind of resistor was that. By the way, make sure no other bad components corresponding to this resistor.

Jestine

==========================

Good Day Mr. Yong

Sir can you help me to solve my problem regarding my Acer Monitor AL 732 i have 10 pcs already got problem some shutt off a few second and some white screen ist it posibble to repair what spare parts to be replace Hope you can help me to solve my problem.

Thanks

Ronald

Hi Ronald,

White screen is due to bad LCD Panel. before that make sure the cable connection between the mainboard and lcd panel is conected properly. And also make sure there is supply voltage to the lcd panel. Display shutdown usually due to one of the backlight have problem. Before that you need to check that the inverter ic is getting supply voltage.

Jestine

=======================

Dear Sir,
I can’t understand 1 difficult problem, I have 1 Msi motherboard it is not going on power, SMPS, PROCESSOR, RAM all is ok but motherboard power not going on. prcessor fan not running & smps fan not moving when short power switch .
so plese help me how to test which components in motherboard is problem

thanking you
yours truly
Pintu

HI Pintu,

It can be any component have shorted like the CPU, capacitor, transistor, north/south bridge IC and etc. It is not easy to check this kind of problem. You may need to unsolder those component and power it on. If it can be on then you know where the fault is.

Jestine

=========================

HI Dindo,

I hope your fine I have problem with this tv wherein the display is dark
although you could see the video with color but it is dark.I open the back cover
and observe the heater it is not glowing turn off the power and perform resistance
check on the heater pins "HT" after removing the yoke board it seems ok.I try to check
also the heater windings and it is ok too.I dont have tools to check the heater voltage
because the regular DMM cannot measure it.Can you give me advice how to solve this problem.I Attached diagram.Thank you and more power!

It could be a weak tube. Try visit this link to see if the picture tube can be brighten:

http://www.repairfaq.org/sam/monfaq.htm#monbrocrt

Jestine

======================

HI John,

I have not trying hard enough on my electronic hobby. I do enjoyed learning so much about it. Fact I bought ESR kit and install it was fun.

Noted.

However I’m confused how to read it when testing different type of caps. I wish I had some a book to keep me in handy of all those
components to understand from ESR. There are so many ways I would like to do to make some money as part time repair electronics.

You can refer to this link:

http://members.ozemail.com.au/~bobpar/2003esrchart.txt

Any value that you get higher than the chart then you need to replace it.

Fact about me is I’m deaf since birth but I do wear cochlair implant on one side to an able me to hear well. I live in USA, Colorado.

Noted.

I would love to buy from you a study book. Unfortunate, I’m unemployed which limited my income. So I would be glad if you help some idea to start repair on electronic. If I can earned some small amount of dollars to build up.

I suggest that you visit this link as i found it to be very good:

http://www.repairfaq.org/REPAIR/

I have no idea where to start. Fact is my first TV repair I did from Samsung 46 inch flat screen TV was a bad caps from power supply that too long to start up my TV. Before I have ESR
I only found five bad caps blown out from top aluminum which shown a dome. I learned this from YouTube videos. After I removed bad caps
installed new parts to increase voltage but keeping μF the same amount. My TV start up quick as new as it should. I was excited and happy
I saved my dollars against TV repair cost. So now I’ve been thinking could I do that repair at home as part time.

Yes you can do the repair work from home but you need marketing skill also so that you can get people to send items for you to repair.

But I have no idea how much should I charge to new customer for just a repair.

Get some ideas from other repair shop. Charge lower than the repair shop because you are operating it from home

I also have no idea what customer would say or asking me some questions. I may feel some stupid ways like are you licensed, etc.

You can tell the truth that you learn from your own experience. However, having at least a certificate can be an advantage. You can take some online course like http://www.pennfoster.com

I also enjoyed reading from you.

Thanks.

Jestine
=============================

HI Rob,

just a few quick questions
when testing a high voltage capacitor with an insulation tester does it have to be an anologue tester or could a digital one do?

Either one can do the job

what results should i be seeing with a good capacitor and a bad one ?your book just says to use one its not clear what results would be

If you use analog meter the needle should move up and then drop back. As for digital one you can refer to this link:

https://www.jestineyong.com/?p=2841

Jestine

==========================

hello sir

my i ask you for help on repairing an 19" lcd monitor
the problem is that as i conect the AC plug to the aoutlet the monitor turns on for few seconds and turns off.
i checked the power supply volteg output and see that in is ok. 15V and 5V .i checked all the componnets and did not fing any defects.capacitors diodes .are ok.
i cant fegure what to do next .
the model is:MJ9BNK
of new vision
thank you

david

HI David,
You mean the power turn off or the display went off? The power LED still on or off? If the power led is off and you get good voltages at the mainboard then the MCU is at fault.

Jestine

=========================

Hi Paul,

Thank you for sending back the link for the bonus reports, when I get time
I will build these two projects.

Ok noted.

The history of this SMPS is that it comes from an Oympus BXF50 microscope
which has been damaged with water through a leaking roof. It has a
separate power control board (connected via ribbon cable) which is used to
adjust the intensity of a 12V 100 Watt Halogen bulb. The display board has
a LED array that lights up to indicate the users choice of intensity done
through a sliding potentiometer. The SMPS uses a circuit to power up the
AC supply (Q3 I think) which is working i.e. We get AC mains power to the
bridge rectifier (D1).

Noted.

The fault is identified as no power output to the 12V 100 Watt Halogen
bulb however the display LEDS are constantly flickering at a low level and
don not responds to moving the pot up and down. I have already done some
investigations and am now removing components to test them but it is
taking a long time.

I have already done the following and am now having to look much deeper
which is where I am going to use your ebook. I think I have identified the
components correctly below!

1) Swapped out the bridge rectifier (D1)
2) Changed power FET (Q2)
3) Changed switching triac (Q1)
4) Changed voltage regulator (IC20)
5) Tested shottky diodes (D20 & D21)

None of the above actions made any difference and the waveforms remained
exactly the same (I have an oscilloscope, a DMM and analogue MM). However
I have learnt through your book to use the hot ground for my scope probe
clip on the AC side which I need to try out and see what the waveforms
look like then.

My gut feeling is that the issue is on the DC side, the DC waveform looks
very un-rectified and sits at a low potential, definitely not 12 V.

Assuming if I’m the one who is repairing the power supply, I will remove the power transformer and check all components (I mean all components) since the water could easily short one or more components in it. If you have an ESR meter and the Blue ring tester your troubleshooting job will be must easier because you can find out bad e-cap and check for shorted primary winding in the power transformer. Yes I know it will take lots of time but since the circuit already been hit by the water the only choice we have is to remove one by one the component and test it off board. Please keep me update on this repair.

Thanks so much for your time.

No problem.

Jestine

=========================

HI Richard,

How are you?

I’m fine thank you.

I hope your keeping busy.

At current busy cleaning up the office because need to renovate.

I’m having a problem with a NEC LCD1555V 15 inch LCD computer monitor. I know its an old one. Ive attached pictures of it and was wondering if you have seen this power supply. The primary supply is good but I have no secondary supplies. I have 3.3volts and 4.9volts on U1 a SMD IC that I’m thinking is the power IC but I cant find any data on it. It is number 203X6 PXAW. Let me know what you think. Thanks for your time and help.

Sometimes manufacturers came out with different part number but with the same internal spec. I found one in the link below but i cannot confirm if it is the same as the above part number. You may need to compare the 203×6 IC pin in the power board with the datasheet of NCP1203D60.

http://pdf1.alldatasheet.com/datasheet-pdf/view/83111/ONSEMI/NCP1203D60R2.html

If all the components check to be good in the power supply then you may need to replace the ic and retest.

Here is a website that sell the part:

http://www.utsource.net/NCP1203D60.html

Jestine
http://www.JestineYong.com

================================

HI Lito,

gud day sir justine,

Good day!

my customer bring on to me a dead pc. I shorted the PS-on then the atx pwer go on, I connect with the motherboard, then the cpu goes up, but the monitor has blink. I check the 12v on the yellow cable of the atx pwr supply. i got 11volts. where do the culprit hiding sir?

Try check the filter capacitor first located in the secondary side using blue esr meter.

I have also one pc monitor when you power up theres a tic-tic sound.

Follow the link below:

http://www.electronicrepairguide.com/testing-flyback-transformer.html

dvd player also brought in lexing brand made in china, when you power up the dvd drive will continuesly open and close…i reheat and reset the cable connector on all terminal going to to mainboard.

it can be the problem of bad laser because if the laser does not work no feedback signal will be sent back to the mainboard thus the mainboard will eject the cd. Before this make sure the power supply is generating good and stable output voltages.

Jestine
http://www.BestElectronicArticles.com

==============================

mr jestine

i checked the supply voltag on the conector that connects the power supply to the video card

there is 15 volt and 5 volts even after the display shuts down.so i understand that the power suplly works good.

i do not have good lamps for cheking .that is way i disconect one by one i did not know it is not corect to do it.

is there any thing more i can check on the boards excluding the lamps.

thank you

david

HI David,

make sure the ballast capacitor are good, no dry joints in the high voltage transformer and that the top and bottom backlight high voltage transformer have similar ohm reading. If all check to be good then suspect one of the backlight have problem. you need a good backlight to make the comparison.

Jestine

=============================

Hi Jestine,

I send you a short video of the actual dim display problem
of the LG TV. I will try to do the isolation method and inform you of the result.
Can you send me total price of the blue esr meter and blue ring tester plus
shipping charges here in Jeddah Saudi Arabia. Thank you very much for your support.

Regards,
Dindo

HI Dindo,

The tv has a constant display except that there is dark picture in between the time when it is displaying. In that case i don’t think is the crt tube fault. I suggest that you check the G1, G2 and the R,G B points in the crt board and make sure all the voltages are constant assuming you are running the tv under dvd player in the pause mode.

Jestine

================================

Sir,
The company PERFECT THE VISION lcd with DVD . The problem this lcd combos , when power in, the red led is glow then push the power the blue led glow and CCFL tube glow friction of second. Then 30 second later the power led glow red and blue one time.
Scaler bord socket connection, GND-ADJ-BL ON-12V this connection goes to inverter bord . ADJ voltage is 1.28v and when push the power switch BL ON voltage is 5 volt . but 30 second later this 5 volt is miss. This time red and and blue glow one time.
no light on the screen. How i solve this problem.

Yours faithfully
Nihar / Kolkata

Hi Nihar,

This seems to be the problem of a fail MCU. This type of symptom were quite frequent in Samsung LCD . If it can happen to Samsung LCD, it can happen to any LCD. Try spray coolant/freezer to MCU to see if it will still shutdown or not.

Jestine

===============================

do you see any varisor in this circuit?

HI Safdar,

It is difficult to tell from the slightly blur photo because varistor can be like like a capacitor too. Check the board marking, if it is mark as "C" then it is capacitor. if it is mark as "Z" or "V" then it is a varistor.

jestine
http://www.JestineYong.com

===============================

Hi Jaan,

and thank You for tremendous teaching material, a great book-the smps repair book. This will be my hammock reading for the summer along with other books I bought from You.

Thanks for the support!

I’ve got a atx ps, almost new, with no output at all and I’ve located a burnt toroidal coil on the secondary side. The coil has three windings +5V, 8 turns, +12V, 18 turns and -12V also 18 turns (but the -12V windings in- and out-put directions are the opposite of the positive voltages). The temperature has been very high, the enamel on wire has gone away (short circuit between all three windings) and the paint on the ferrite core has evaporated as well.

What do You think could have been the scenario leading to the burnt or blown coil?

The first thing i wish not to see in the atx power supply repair is the toroidal coil. if it burnt then there is no toher way to repair it other than to replace with the same coil. The problem is most of the coil are unique thus we have a hard time finding this part.

Did something break before the burnt coil or did it possibly cause anything else to break?

It can be the quality of the coil itself have problem or shorted components that had caused it to burn. Sometimes a bad fan may cause the coil to run hot and burnt too.

Can I use the same ferrite core and rewind the three windings with the same amount of turns and thread diameter or has the core changed its properties?

You can do that if you have the material and the time but it has to be precise.

Please keep me update on this repair-thanks.

Jestine

==============================

Hi Ross,

First of all, many thanks for your ebook "Troubleshooting and Repairing
Switch Mode Power Supplies". It is a very helpful book.

You are welcome!

I currently have a problem with a SMPS and I was hoping you could help
me. It is a Liteon PA-2461-1A SMPS, and very similar (perhaps
identical?) to the one you have in Figure 1.2 on page 10 of the book.

Noted.

The SMPS has two DC outputs — one is -48V and one is +12V. The -48V
output seems to be working, but the 12V output exhibits the following
symptoms:
* when AC line power is first applied, the output rises to 5V slowly
over around 20seconds.
* It remains at 5V for around 30seconds.
* It then jumps up to 12V and a crackling noise is heard.
* If power is turned off, the output drops to 0V over around 40seconds.
* If I turn AC line power off, and then on again shortly after, the
output goes up to 12V quite quickly, but the times vary.
* If I turn AC line power off, and leave it off for a long period (eg. a
couple of hours), then the symptoms repeat from the beginning.

I have been measuring all the voltages without a load attached. Earlier
on, I did try connecting a load (50Ohm, 50Watt) but it didn’t make any
difference to either the 50V output or the broken 12V output.

I do not have a schematic for this power supply, and I can’t find one on
the internet. I have been attempting to trace the fault using a
"generic" SMPS block diagram, but so far, I have had no luck coming up
with a solution.

Could you offer any advice, or suggestion of what to check.

Have you check the components along the 12 volt line like the filter cap and directly replace the 12 volt output diode?

Also, I was wondering if you could tell me what the function of the two
small transformers on the supply are. There seems to be one small
transformer near each larger switch mode transformer

It can be a feedback transformer but with a schematic of that model it can be well explained.

Jestine

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Jomar

July 9, 2011 at 4:52 pm

hello,

i am one of millions of avid reader to your blogs. i am also into repair hobby it's just that i am that professional or good in such field. i encountered this very simple yet so complicated problem with i currently repaired, a money fake detector wherein one of the 4 big capacitors with part number 105j 400v was busted. ive tried to find it in our local electronics stores but failed to find one. now my question is, what is the best substitute for this? hope you can help me on this. thank you so much in advance.

best regards,
jomar

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admin

July 9, 2011 at 8:40 pm

HI Jomar,

You could use a higher voltage but with the same capacitance or you can use this formula:

http://electronicrepairguide.com/series-and-parallel-capacitors.html

Jestine

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Onyekachukwu

February 7, 2019 at 4:21 am

Hello,my Prof. In electronics, I am very grateful for all article, I know someday we shall see each other face to Learn and share from your ocean of knowledge. Thanks

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