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Electronics Repair Questions/Answers and Testimonials- Part 40

By on December 25, 2012

 

Hello Jestine,
i have been having some problem with components testing and i want to
ask some question.
Considering the test for diode, when its forward bias, a value is
shown on the screen like 419 and when its reverse biased a new value
when gives not much diffence is shown on the meter screen like 550.
with this, will i say the diode is good or bad?

Also the second is this: i have tried reading a capacitor on some
boards but i found that its gives no reading irrespective of capacitor
range both on the micro- and nano- frad range but when i switch to the
resistance range to test, its reads some values, sould i say the
capacitor is good or not?

Hi Emmanuel,
If you measure a normal diode using the diode range test and got two readings means the diode is shorted/leaky. Capacitor have to be tested off board and the value should be tested using digital capacitance meter. A too small capacitor( in pf range) may not be able to register on your meter.

Jestine
 

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So different brands do they use different waveforms and do i have to
look for a diagram for certain brand in terms of waveform and test
point or there is another way?

Hi Thulani,

Waveform that you got from the test points should be the same. If you have the schematic that would be an added advantage. Otherwise you may have to find your own test point to test it.

Jestine

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Thanks mr jestin it was one of your statements an open resistor around pincushion circuit. Thanks you have been so helpful.

Mr Bello

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hi mr jestine you are greate person in that god have bless us with i would like to say thank you for sending me those article they have helped a lot all thou i have some questions for you i was testing tv with only standby mode i tested the powers all get is a missing 5volt that supply the ic m61260 just trace back but i couldnot understand becouse the transistor 2sc2383 on the middle pin i find 11 volt on other pin left and right no power but when i test similar transistors the other middle have 11 volt outer pins 5volt so the 3rd transistor 11v middle and left 6v but right nothing so pls help me.

 

Hi,

It could be the tv cpu not sending an on signal to the transistor to turn it on so that 5 volt can be obtained. Or it could be surrounding one of the resistors already opened circuit. Check also the transistor for leakage.

Jestine

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hi sir jestine 

I hope you will be fine.

I found your article about 19'' samsung lcd monitor.It is very helpful to understand

    the problem related power board.And solution find way.Thanks for the article .I am new in lcd

    repairing so i have  not full confidence to repair lcd because i belong to a little city of m.p.(madhya pradesh) REWA .And i have no latest instruments like CRO, ESR meter etc.yesterday a         21''samsung lcd model no. LA22D404E4R come to my shop for repairing. The problem was no display only standby led blinking.When i open the cover i saw the some chip components like registor, capacitor transistor were burnt beside vga connector slot.The costomar tell me he use the

   lcd in place of computer monitor and the unit works fine but he plug the cable connection in lcd on

   position then the problem create.But i have no replacement part and no idea to find these type of

  component because the part number were burned.so please tell me how to solve  this type of conditions.And  at last my english is weak so please try to understand my matter. Thanks.

HI Shameem,

In your case the only solution is to find the right schematic to locate the exact value or you have to find the exact model for comparison. Other than that it would be hard to repair a board that have many burnt parts.

Jestine

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Dear, Jestine Yong

Firstly I would like to thank you for your information that I found in you 
website which has already helped me to repair my LCD LG Flatron Wide 
L194W-SF which has no supply. But thanks to the step by step video and 
picture it took me few minutes and a little bit of solder following your 
information that I found it great , even someone that don't even know 
nothing about electronics can do it easy. I changed the same capacitors you 
mentioned and I have also ordered them from the link witch you provided for 
the kit. The same day the kit arrived I fix the LCD. I am impressed of how 
accurate you were and I save also MONEY.
Thanks a lot,

Charlie Z,
MALTA

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hi, i have lcd toshiba tv it has sound ok, video ok but no backlght! when i startup the tv displays video with backlight on for one second and backlight switch off.

i tested the power connector between inverter and psu it reads 23v instead of 24v, i also check HVT on the inverter i found one of them doesnt read 300 ohms it is open, but i didnt check secondary caps of psu!

do these problems may be the cause of the problem?

thanks

Hi Amri,

Yes that could be the cause of the problem because all the HVT should have the same ohm range be it in primary or secondary winding.

Jestine

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Thank You Jestine,

I have one more Question are mosfet drivers,IC's also known as PWM ic's.If so,if the Mosfet driver (PWM)ic is supplying high current to the Mosfet can we replace the mosfet with a higher value to resolve this problem or should we replace the Mosfet driver(PWM ic).

Regards,

Uday.

HI Uday,

Mosfet alone in power section is called as power fet. Some of the power fet can be integrated into the pwm ic . If the power fet have problem you can try find a higher spec to replace it but not pwm ic that have the build in mosfet. No matter waht the best is still use back the same part number.

Jestine

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Hi Stephen, 

For the ICs is there any instrument to be used for checking them and do you need to find any resistance or something else?

It depends on what type of ic you are checking. There are many types in the market and generally people use Huntron tracker (huntron.com) to compare the signature of the ics.

Another thing when a TV takes quite a long time to begin seeing the picture what could be the problem?

Bad picture tube or the heater voltage not good (from the flyback).

Jestine

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Hi Jestine

I am facing problem in Samsung Samtron 56v monitor, the problem is when i open vga cable from CPU ,the monitor displays as usual i.e. check signal cable. But when i connect it to cpu, then there is no light and front indicator blinks and relay chatters about three seconds interval. I have checked H.yoke and its related components and not found any defective component. One more symptom i found is that when i open the HOT but vga cable connected then the same result found (LED blink and relay chatters), when i open the vga cable the LED becomes stable.

Hi Gopal,

This is a common fault of bad monitor CPU.

Jestine

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Hi Jestine,

I have a variac which produce AC & DC.
Is it isolated and could be say as isolation transformer? 
Based on the principle of Isolation Transformer, the grounding/earthing is independant.So I did a continuity test at the earthing terminal on primary and secondary side.
It's not continued/shorted each other.So,is that the right way to prove that the transformer is isolated?
Thanks.

Best regards,
zahirin

HI Zahirin,

Unless your variac is fully isolated. I suggest that you visit this link:

http://www.electronicspoint.com/variac-isolation-transformer-t68798.html

Here is my old post:

https://www.jestineyong.com/variac-is-not-an-isolation-transformer/

Jestine

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Good day Sir Jestine,

I am planning to buy insulation tester. What I saw in the electronic store is Wheeler model W-2000 insulation tester. I don't find any website regarding this model. The manual is somewhat lacking in explanation regarding testing of capacitors. Even if I buy this meter, I don't know how to read the result and what should I expect normal reading and abnormal reading of a certain high voltage rating ceramic capacitors. In other words, what should I expect for a normal reading of ceramic capacitor used in TVs, monitors and other high voltage circuits.

Thanks,
Lemuel

HI Lemuel,

I have not use that insualtion tester before thus I can't give advice on this. Try check out the review in my blog post link regarding the meter that can test high voltage ceramic cap:

https://www.jestineyong.com/review-of-the-dy294-digital-transistor-tester-part-1/

Jestine

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Hey Jestine,

 Thanks for your Emails, they always make interesting reading.

 

I have only started with Electronics in the last year or so (although I have always been doing Automotive Electrical). I have made about 10 kits that have been successful. I have made a Pulse Width Modulator kit and although it worked well for a while, it now is not generating a pulse. I have done testing at the IC and it appears that is the fault. I watched one of your videos on YouTube the other night on testing capacitors and you took it out of the circuit. I know that with many components you have to take it out of the circuit to test, but are there any components that can be left in the circuit when testing?

Cheers

 Mark

Hi Mark,

Electrolytic capacitor can be tested in circuit by using ESR meter. Other components that can be tested on board are, fuse, coils, thermister and LED. I prefer to  test other components offboard like diodes, transistors, zener diodes and etc is because it gives a more accurate reading.

Jestine

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Hi Sir i know it is the long time without communicating
I have a problem with a 54cm Ultronic TV .
I have found that ceramic cap @ the primary side of the power supply have burned
Changed them and cheched if it is still running on normal voltage.
I switched on the tv all to find out the left and the right side of the screen are coming together 
making the looked squashed in,if you have an idea of what i mean pls try and help.
Thank you.

Hi Benneth,

In this case you may have to check if the B+ voltage to flyback is enought or not. Check also for shorted modulation diode at the flyback area. There is one pincushion transistor that is attached to heatsink-make sure it is not shorted.

Jestine

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Dear Justine, Thanks for the latest newsletter, I found it vary informative
as always, I always enjoy reading them.
I also tried your methoed for finding
the value of a burnt resistor that I
read about in your book How to find burnt resistor values, it worked really
well,thanks for the help and keep up the
good work. Best wishes. George

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Dear Jestine Yong,

   My friend from Canada told me the electronic magazine in Canada vanished. It indicates that those youngsters or hobblists of electronics are getting less so the magazine can't survive. It alos happens in HK that very few youngsters like electronics or science.

   I wonder if the electronic professionals are getting less for the young generation getting popular at online games. Are those repair technicians getting few as well? There is basically no repair shop in HK.

  What do you think of the trend and our prospect as electronic professional ?

Thanks

Frankie Leung

Hi Frankie,

You are right the repair tech is getting lesser most probably due to less profits in the repair trade. But electronics repair is not limit to consumers electronics repair. There are:

industrial electronics
medical electronics
automotive electronics
robotic electronics
beauty equipment electronics
cctv/alarm electronics
car parking electronics
house building electronics
etc.

Jestine

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Thanks alot of  your helping. sometime everyone have eye  but  every time cann't see. At this time ,  your repair books are give the light. So everything can  see. I  also  helping the beginners. Now you are great  person. Very  high power. you are  look like  SUN. I am a candle light.

 I wish to you and your family,  PEACE,HAPPY AND WEALTH in from now on candle  light

kyi tun

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Dear Jestine,
Thanks for the wonderful message, please take care as well. I have enjoyed all your News letters and they have been helpful. Can you please solve the following problem for me.
I connect an LCD monitor to my computer, the following appears on the screen "ANALOG OUT OF RANGE   53.8KHZ / 85HZ"
My computer is Pentium 4 operating software is Windows XP Professional Service Pack 2.

Beat regads.

Redwell 

Hi Redwell,

Try use another monitor to see if the message appear or not if no then change the setting (right click) to run lower resolution. Now put back your old monitor and test it and if the message still appears then the MCU ic in the mainboard have problem.

Jestine

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My aunt from Spain brought a washing machine and dryer here in our country. 

Both machine needs a power of 220 VAC 50Hertz to run correctly but our electric standard here in our country is 220 VAC in 60Hertz. The machine is running in slow motion and the timer is acting weird. I went to electrical store and ask them about it, they advice me to use an AVR ( auto voltage regulator) with 220VAC 50h/60hertz. Is it true Sir?    Thanks a lot Sir and GOD BLESS.

Hi Noli,

I know that it will surely affect the timer but no info on the motor (perhaps it could go overheat). In your case I suggest that you bring along your dryer and test it out on AVR. If it works then buy it .

Jestine.

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HI Jestine,

I want to replace diode RL207 with exact same value number but here in my local market there is not available this type of diode.I chked its datasheet its just a general type diode of 2A, 1000V Peak reverse breakdown voltage.Tell me which diode i could replace this. Can i use TVR4J diode in place of this diode.Can i use fast switching silicone diodes 4 this type of diode with nearly equal e-rating.

Secondly i want to replce NTC 2.5D-11thermister but same this is not available in market.I cheked it with ohmmeter but it showed around full deflection on analogue meter.I suspect it as a faulty. Wht do u think abut this ohm test.If it really faulty, Can i use any fuse in place of this thirmister.Thankx in advance 4 ur guidance.

Naeem

HI Naeem,

You can try UF5404 diode to test it out. A good thermister should have low ohm reading and I guess your thermister is good.

Jestine

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