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Electronics Repair Questions/Answers and Testimonials-Part 36

By Jestine Yong on October 9, 2012

Hi Jestine

Just thought I would email to let you know how much I enjoy your Monthly newsletters

I find them interesting and full of practical solutions

Just wish I could attended one of your training courses

Keep up the good work would be lost without you

Thanks

David

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Hi Ola,

sir,
1. can I use 1N4148 zener in place of 1N4148 silicon doide.

1N4148 is a silicon signal diode and is not a zener diode thus is no need to find replaement. It is easy to get from board or from any electronic shop.

2. Can I use recovery rectifier doide 50-1000v, 2A in place of bulk doide at inverter circuit of Dell lcd e172fpb (100v, 3A).

I suggest that you use back the same type of diode with same or higher rating.

3. Can I replace ic cd4015b with cd4011b. Thanks.

Both are different thus you need to look for the original one.

Jestine

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Hi Mr. Yong,

After having waited for a full week, the ordered resistor and power IC finally arrived. So, I immediately replace the defective e-cap, resistor and the power IC. Once done, the power supply came back to life and delivers the expected output voltages.

Then, I put back the power supply into the Scientific Atlanta Explorer 3200 cable TV digital terminal, I connected the power supply to the main board, turned ON the unit and it starts to work as expected.

Another successful repair!

Thanks to you!

Stephane

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Thanks very much you are great you doing wonderful job to help the electronics technician know what to do exactly, i want to ask you have you ever work on Thomson tv model number 40N90NH22N, the tv came to me for repair but only standby light come on, if i press the power button nothing happen it will not come on to screen what you think might be the problem?

Hi Abdoulie,
I have not repair that model before but for any tv that have stand by light on the problem could be due to bad cpu, bad eeprom ic, bad optoisolator circuit or even the main power supply have problem. Did you get any supply voltage to the main power, power ic? If the cpu did not send out any signal then the opto isolator ic or relay (if the tv use a relay) will not conduct. if not conduct then there will be no output voltages from the main power supply.

Jestine

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How are you sir?i have been reading books i would like to ask a
question,how does a power supply without a RELAY switches on from an
ON COMMAND to switch the whole power supply

It uses the optoisolator ic to turn on the power ic in the mainboard to produce the full output power. The signal from the opto ic is coming from the cpu at the secondary side.

Jestine
http://www.JestineYong.com

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Hello Mr. Jestine

I am working on a Samsung Monitor (CRT), the fault is horizontal wavy lines on the picture. I have checked for dry solder on CRT board and even replaced the CRT base, but problems remain same. Sometimes picture becomes normal but after few minute, wavy lines starts . I have attached the video for your reference. The problem appears like a dry solder but there is no dry solder and no crack on board. Is this the symptom of CRT fault. Finally i have decided to replace the CRT. Please suggest your opinion.

Regards

Gopal Sharma

Hi Gopal,

No it is not a crt fault. it could be the problem of bad horizontal/vertical oscillator ic, bad cpu or even eeprom. If you have the scope you need to monitor the output waveform of the vertical/horizontal output to see if it is stable or not. If not stable then direct replace the horizontal/vertical oscillator ic.

Jestine

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Hi Jestine ,

Want to find out from you , can i replace ic UC3842B with UC3843AN . Thanks

Hi Chong,

Some power supply can work but to some it will not work and even if it work sometimes it could give minor interference problem. I suggest that you replace with the same part number.

Jestine
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Hi Jestine, I have a question for you. Have you ever come across components in a power supply that are hard to de-solder? How do you go about de-soldering the component without damaging the trace or the components?

Best Regards,

Andre Gopee

Hi Andre,

Lead free solder usually need much higher temperature to melt it. I suggest that you get a higher wattage of solder gun with the right tip to do the job. You may also ask any electronic shop in your country to remmend the good solder gun for the job.

Jestine

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hello Mr jestine

how are you?

why when i test good led with analogue meter at x1 its good and bright

but at 10k its behave look like normal diode but (without bright )

my question : why it doesn't bright

Hi,

I'm fine thanks. Because the ampere in x10 k is too small (probably in microamp) while in x1 Ohm have about 150 ma.

Jestine

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Hi jestine,

I must confess,i'm really enjoying your smpsrepair ebook,nice work.

However,under i/p protection and EMI filtering ccts,you mentioned;X&Y capacitors for differential and common modes EMI reduction.why are they X&Y?
What is differential mode EMI and common?.Thanks.

Michael

Hi Michael,

Please visit the link below and you will have better understanding because it has pictures in it:

http://www.murata.com/products/emc/knowhow/pdf/26to30.pdf

Jestine

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Hello sir
How are you?i hope you are fine with dairly activities,am fine too.
I want to know more about current sense resistor,how can identify this
is current sense resistor,how it is look like,its minimum and maximum
value,the place where is used in the circuits like Tv /Monitor
circuits,its image will be very helpfull if you send together with my
answers.
Have a good day
Thanks.

Hi Amosi,

Current sense is just like a normal resistor and has a value from 0.1 ohm to about 0.68 ohm and it is located in the primary side nearby the power fet. If you see only one low ohm resistor in the primary side that one is the current sense resistor.

Jestine

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Hi,

1=I have a china tv which I got from client crt was burnt at the 180v wires I
resolder wires sound is ok but heaters are not on.I changed three transistors
on CRT i.e.C2482,A1015,LOPT even miccro i-c LA76931k G2 is 542v problem remain
the same

Heater voltage from flyback and if flyback did not energize it will not produce ac voltage to heater element. You need to make sure there is B+ supply and pulse signal to HOT.

2=The other China keeps on blowing the line drive transistor.I change
Lopt&capacitors which were swollen around the lopt but no good results.

Check this link:

https://www.jestineyong.com/why-horizontal-output-transistor-in-crt-monitor-get-shorted/

3=I got Sinotec it has horizontal line I changed vertical I-C,swollen
capcitors around i-c I also micro i-c LA76810as but good results

Check the supply voltage voltage and the vertical yoke coil for open circuit.

4=Lastly I got SINOTEC COMBO(DVD PLAYER)This one gives horizontal line sound
is ok Ireplaced the vertical i-c,micro i-c 8823CPNG5RH6 and its eeprom. I
think you will help me on this problem .I got these tvs in JUNE last year

Check the supply voltage voltage and the vertical yoke coil for open circuit.

Jestine

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

Hi Jestine, I am repairing a Power rectifier and I am following the steps from your book; Chapter 11 on the simple steps for voltage testing and Step 1, I measure the AC input, measured Ok, then the Filter Cap, measured Ok, but when I reach the power IC I got 0.7 volts so I trace back to a SMD resistor what looks like the start up resistor, but I am a little confuse as to the value of the SMD resistor. Its marking is 01X which I believe to be 10 ohms with a tolerance of less than 1 %, when I measure it out of circuit I am getting 50 ohms which means that its value has gone high. What is confusing me is the I thought the start up resistors value suppose to be off high value and off high wattage. This resistor package is very tiny., could be 1/20W or 1/16W. Can I replace this resistor with a normal resistor and a tolerance of 1 %? Let me know what you think.

Hi Andre,

Then I suppose the low ohm resistor could be a protection resistor. Some ICs will not get supply from the start up resistor. It will get the supply straight from the source (about 300vdc) and the supply will be lowered down in the IC itself. Try check pin 8 (HV) of the ic 1203p60 and you will know what I mean:

http://pdf1.alldatasheet.com/datasheet-pdf/view/83116/ONSEMI/1203P60.html

Jestine
http://www.JestineYong.com

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Dear Jestine,

Thanks for your email.

I am the computer engineer in Hong Kong. I have so many default ATX power supply default.

Most of the problem is that when the computer turn on for some min, then it turn off at once.

When I change the power supply and it is ok.

I have the ATX power supply voltage testor and test all the default power supply is low voltage.

Would you mind to help how to fix the problem?

The brand is SPI and Gigabyte.

I am looking forward to receiving your reply soon.

Thanks

Banny

Hi Banny,

There could be few faults to your power supply problem. It can be bad filter caps in primary and secondary side. Bad secondary side IC or even bad components in the optoisolator ic circuit (if have). Sometimes resistance value change can happen in the secondary side as well.

Jestine

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I want to repair huawei HG553 vodafone station router. When I switch on it no lights. Then I touch each components. I have seen that Boardcom BCM6358 chip is getting very very hot.
I couldn't realize that is this chip is getting hot due to the chip fault or any kind of related component error.

Please help me to repair this router.
I appreciate that if you provide me step by step guide. I don't know where to start repair this router.
I have read your article that you have written before few years ago about router repair. But I couldn't find it now.

Thanks

Hi Narada,

If the chip is too hot to be touch then either the chip itself have problem or the supply voltage is too high. For your information it is not easy to find parts for router.

Jestine

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Hi Jestine,

I have an uncertainly in doing a capacitor replacement and I believe you can help me here.

I am to replace a faulty capacitor, and I have a capacitor of equivalent specs but with connecting terminal outside of casing.

Can I still use this capacitor? If so, are there any implication I may need to be aware of? Attached are the two capaciors.

If you can help, I'd really appreciate that.

Thanks and regards,

Baptist

Hi Baptist,

You can replace the capacitor as long as it has the same or slightly higher microfarad. This means if you have 82 uf cap with 120 volt you can replace with a 100uf cap with 120 or 150 volt. If you are using an external pin cap then you may need to use a shrink tube to cover the metal connector.

Jestine

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Hi Mr. Jestine,

I just have a couple of question for you. Last March of this year I bought these BlueRing Tester and the ESR Meter to you.
I just want to ask you if I can use my Blue Ring Tester to test speaker voice call? My other question is can the ESR Meter capable of testing
electrolytics caps rated 400Volts? Hoping for your reply. Thanks.

Raymund

Hi Raymund,
Yes you can use esr meter to test on 400 volt cap. You just need to jot down your own chart of a good cap and compare it with the one you want to check. As for testing speaker please visit the link below and check on number "8".

http://members.ozemail.com.au/~bobpar/esrhints.htm

Jestine

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Message Body:
Thanks Jestine for the feedback about the Blue Ring Tester that you sent me, really appreciate your efforts.

I still do not know where to find the ECG Philips Master Replacement Guide, it is fustrating to go to the internet cafe, look for a particular Ic then you don't get to find anything related to it for confirmation of the Voltage supply.

Can help with the link for the latest release of up-to-date replacement guide?

I also tried to google Tech Publication recommended from your e-book 'Testing Components like the Professional' to no avail.

Have a superb day!

Hi Jonannes,

Thanks for the support. The ECG replacement book is no longer in the marker because it was bought by nte (www.nteinc.com). You can visit www.sayal.com to get the latest NTE book.

Have a good day!

Jestine

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Jestine,

I have your eBook on repairing SMPS, and I have been benefiting from your monthly newsletters.

I have quite a bit of experience as an electronics tech troubleshooting, reverse-engineering and repairing conventional power supplies as well as other more complex electronics equipment, but have just recently developed the need to understand and repair SMPS. Your book was a great help in grasping the concepts utilized by the SMPS technology. I have recently successfully repaired several Kepco RMX-28A units for one of our test benches. I have also learned quite a bit about the CFL bulb technology, actually repairing some of the electronic ballasts. I appreciate your sharing your experience and insights in this area. Thanks.

Lplett

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

Hi, i have an LG Flatron W1934-BN,the screen goes on for 8minutes then it reverts to standby,then it stays for 10minutes on standby then it comes on again.What could be the possible prblem.

Hi,

Make sure the voltage from the voltage regulator ic in the mainboard is good. If it is good then the problem could be a program in the MCU ic.

Jestine

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Dear Yong,

What is the full form of "CCFL". In your review I can not understand clearly the use of the tester. Where I put or connect the tester and for what? Please explain me elaborately.

Thanks, till then…..

Hi Amitava,

CCFL is Cold Cathode Fluorescent Lamp. The tester has a black and front tip . Just connect the black probe and front tip to any ccfl lamp-that's it. Here is the backlight photo:

http://www.byfort.com/ccfl/CCFL31.jpg

Jestine

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

Secondly i have a sharp crt tv that have the problem of horizontal line i have replace the vartical i/c with good one, the voltage supply to the i/c is 24v i also replace all the capasitors at the vartical side and yoke coil but still there is horizontal line. Please i need your helf.

It could be an open vertical yoke coil or no vertical signal coming from the jungle ic.

Jestine

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

another excellent newsletter, What would be a excellent Newsletter would be what is the most lucrative product to repairout of your
list of EProducts repair guides on your site. What breaks down most and what people will turn in for repair at a reasonable price?
For example Laptops breakdown alot but the market is saturated with repairmen or repairladies. LCD monitor are very inexpensive
so repair may not be a option just buy a new one. As for as the PS3 is concerned less than 1.0% fail compared to the XBox 360
at 30%. Well thats in the US of course.
I allways welcome your professional comments.

Thanks,

John

Hi John,

Thanks for your email. Learning electronics repair is not a must in repairing consumer electronics equipment. One can always work in the industries below

cctv/alarm/door access
car parking system,
medical electronics,
automotive electronics
industrial electronics/cnc machine
beauty equipment repair
Cash register repair
and etc

Electronics repair will never go obsolete.

Hope this helps.

Jestine

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Hi Jestine,

I need some advice on my 21” Dell screen which keeps going off after an hour or more of normal operation.. The symptoms are When first switched on it works well. After an hour or so the screen all of a sudden gets bright and in a flash the image is lost from the screen. The power indicator is always on. When I toggle the analog/digital button at the bottom of the screen switches the image comes and off. After a while (maybe 10 mins)when I try it again it comes on and stays and then goes off after some duration. Could be a component is volatile with heat? Have you come across this and what could be the problem? Regards.

Wilson

Hi Wilson,

It could be bulged e-cap problem. Make sure no bulged e-caps and dry joints in the high voltage transformer. Sometimes a weak backlight may cause similar problem.

Jestine

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12 Comments

Andre Gopee

October 10, 2012 at 6:56 pm

Jestine, Ilove reading your news Letter, It give me insperation. Keep up the good work.
Andre

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Reply
- Jestine Yong
  
  October 10, 2012 at 8:35 pm
  
  Hi Andre,
  
  You are welcome!
  
  Jestine
  
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Hem

October 11, 2012 at 11:53 am

Sir, can i get IC 8 pins number in an electric Grass Trimmer Model :Flymo Samurai TMET 1000XT variable speed module with one Triac. IC number was clean by supplier .Thanks...

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Reply
- Jestine Yong
  
  October 12, 2012 at 9:13 pm
  
  Hi Hem,
  
  Sorry I do not have info on such equipment. The only way is to find the schematic to get the exact part number.
  
  Jestine
  
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Hem

October 11, 2012 at 11:58 am

Sir, I have a LED monitor Viewsonic when i switch ON ok and it go black after a few second .What the cause ????

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Reply
- Jestine Yong
  
  October 12, 2012 at 9:01 pm
  
  Hi Hem,
  
  Have you check if there is any supply voltage to the LED driver iC? Or when you say go black in few seconds, is the power LED also off?
  
  Jestine
  
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dicksy

October 14, 2012 at 11:00 am

hi jestin
i enjoy ur monthly newsletters and find them interesting and full of practical solutions.thank you verymuch.
have a good day
dicksy

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Reply
- Jestine Yong
  
  October 15, 2012 at 1:40 am
  
  Hi Dicksky,
  
  You are welcome.
  
  Jestine
  
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Engineer Aqdus

October 16, 2012 at 5:10 am

dear Jestine yong,
i would like to ask question about smps ,my laptop charger is based on smps design and it has low output power problem ,model of charger is Dell PA-1131-02 plz let me know about the suspected portion of supply which is need to be troubleshoot
thx

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Reply
- Jestine Yong
  
  October 17, 2012 at 5:26 am
  
  HI Engineer,
  
  It could be bad filter caps.
  
  Jestine
  
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rex algon

December 8, 2018 at 12:13 pm

dear sir jestine,

i have a little question to you ...why ic-LA76931k gets hot in a 1minute to up...what's the cause?kindly give me some tips ...that's in advance...

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Reply
- Jestine Yong
  
  December 10, 2018 at 11:44 am
  
  Hi Rex,
  
  It can be the IC itself is shorted or a too high incoming DC supply voltage.
  
  Jestine
  
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