May
20

Electronics Repair FAQ and Testimonials-Part 30

By

Hi Jestine , Thankyou for the info on the dvd video machine , i checked the power suply and found the 5 volt line to one of the chips rather low due to a resister loosing value in other words it was open circuit causing a loss of voltage to one of the chips also on checking the tape mechanism i fount that one of the cogs were out of line , Thanks once again .

James

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Goodday. Jestine can I replace a resistor 2. 2RJ 5w with a 5w 3K3J on a TV power supply.

2.2R means 2.2 ohm and you can’t replace with a 3.3 k ohm resistor . However you can replace with a 3.3 ohm resistor.

Jestine
http://www.JestineYong.com

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Hi Jestine,

I am a regular reader of your monthly repair newsletter. It provides very helpful information and I am learning a lot from them.

I wonder if I could ask you for a help.

I am having a problem in finding what type of a Horizontal Output Transistor is used in Samsung TV model CS-29k40mq. Can’t read it from the existing (burnt) HOT and I don’t have schematics.

Your help would be much appreciated.

Regards

Henry

In this case you have to test out several HOT part number. Once on for few minutes off the machine and see if the HOT is warm or hot. If it is warm then you can use, if it is hot you have to find another part number.

Jestine

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Dear Sir,

Thanks a lot for your mail. I always look at your blogs. From your blogs I have got so many important things which would be helpful in my servicing life.

I wish your success in life.

 

Best regards

Shahjahan

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Hi dear Jestin,

 

hop my mail find you in a good time.

i have a problem with a SONY tv that i just bought it. it was a used tv. the moment bought it, it was not working normally. when you plugged it to AC power (220) it was not coming unless you tapped with hands, after tapping it was coming with good picture and sounds.

i thought that it might have Dry joints and if i re-solder the dryjoints, it will work.

actullay it had a lot of dry joints and i re-soldered them all. but the tv is still not fixed.

some mistake i made. after re-soldering the dryjoints i forgate to connect the Degaussing coil plug too, so when connect the tv to AC220 there was one resistor (470 ohm 5% 3watt)next to this  ”Degaussing coil plug” and it smoked. so i suddenly disconnect the tv, but still this resistor has reading and the color is changed.

after this the tv is not coming even with tapping it. when you plug it AC outlet it just prouduce a sound like “Donggg”, the power lED is ON, no hight voltage and not the heaters are ON. and finally it is not coming.

it you do a voltage test in it you can get the following.

-in the base of HOT no volgate

-in the collector of HOT some voltage

-in the maing filter capicitor you can get both AC and DC voltage (300+)

-in the STR 60707 vcc pin you can get an infinet voltage (AC & DC) while this volgate must by 15v dc.

-sometimes if you touch the STR heatsink or three resistor (15K ohm) near it, it shakes you like AC 220, that means it has AC voltage in it.

-the pissistor is getting hot

So i don’t know where the fault is and i would like you to help me.

Best regards, and thank you very much.

Naseem

HI Naseem,

This is definitely a dry joints. The first thing is, is all the output voltages from the power supply good and stable? If yes then did the TV have high voltage or not? if not check the B+ supply to the flyback and make sure there is a pulse signal to the base of the HOT.

Jestine

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I canot stop reading ur books Mr yong.This is greate and i dont know how to thank you about the knowledge u r sharing with me and others.

I have deside to read all ur boks 10 times each other and u know what!!?? it is not bothering at all hehehe it becoming much more intresting every time i star read:):)

Every time i read ur books i find something new.

Now i dedicate my time to SMPS book and i must learn  those 11 circuits.

U r so wonderfull Mr young im sory i canot be in ur class there so i can learn directly from u but in the future i hope i will se u live

so i can thnx to u directly.

THank you so much again from ur friend from macedonia.

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Hi Gasant,

Today I remove a component because I wanted to see what is was. At that time I knew it was a Fet on the primary side of smps. However it turned out to be a 5 legged power ic. Am I correct to say fet and the pwm ic is combined in one as there is no other pwm ic in that vicinity.

Yes you are right.

After resoldering it back on the board and with part no CQ0765RT I could now check pins.

1)      Drain—-650V

2)      Gnd

3)      Vcc—– Which I assumes is input volts  is– 20V

4)      Vfb

5)      Sync

This is where I get confused. Am I allowed to do this procedure regarding drain measurements.
1)  Black probe to hot negative

You are correct.

2) Red probe on drain

Usually the voltage is high in this pin.

or secondary winding pin of primary side of transformer
3) I get a reading of 420+ v to/on  secondary winding pin of transformer

Does that sound right.

No you can’t test the secondary winding because it is a high frequency ac and your meter can’t test it.
The value that you got was in correct. You need to measure the dc voltage after the diode (that is connected to the secondary winding pin). It is common sense because when you get good dc output voltage then it is not necessary to check on the ac voltage.
Problem 2

I have tried the secondary voltage output line test after diode by using analog meter on x1 ohm range.
Red probe to cold  negative and test with black probe.
Will you please help me with some advice.

1)      Diode output no1 * B+ output line not registering any ohms. But I get a dcv reading of 67v

2)       Diode output no2 * Registering ohms slight movement . Dcv 6.6 v. Returns to VFB of power ic   through the opto isolator.

3)      Diode output no3 * Not registering any ohms. But get a dcv of 9v.

4)      Diode output no4 * Registering ohms slight movement . Dcv 6.9 v. Supplies audio control ic  TDA7056A with power

I did two separate tests

Does that mean D1 & D3 has problems somewhere on the board even though  showing dc volts.

First you need to know that you cannot perform separate test on the same line when there is good voltage. As mentioned in the ebook, the ohm and voltage test are different. If all the output voltages are good and normal then it is not necessary to check on the ohm of the diode because the smps is already functioning.  You need to perform the ohm test is when the smps can’t start due to component/s shorted in the secondary side or load. In this case you can use the ohm test to check on the diode and see if the ohm value is increased or not.

Jestine

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hi mr jestine. i have a problem with a lcd monitor ( viewsonic vg500). this monitor uses an external 12V POWER SUPPLY TRANSFORMER. the problem of this monitor is: there are discontinued lines on the entire screen( see joined video). have you ever repaired this fault?

i don’t know if it is a power supply fault or scaler fault, please can you help me. thanks.

If the power supply output voltages are good then the problem could be in the lcd panel or the mainboard. Make sure the mainboard is getting good supply voltages from the voltage regulator ic.

Jestine
http://www.JestineYong.com

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1. sir, i want to know schottky diodes marking code. Please help
s.diode starts with which code ? 2. I saw ‘how make Esr meter’ from
your erg member site but range only 2o ohm. Sir, please give me
another project of esr with high esr range. Like blue esr mtr

 

Hi,

There are thousands of schottky diode part numbers. You need to read the code and find the datasheet. There is one example 1N5817.

AS for the ESR you can see the diagram below but you need the PIC chip to run:

http://www.anatekcorp.com/BlueESR.pdf

Jestine
http://www.JestineYong.com

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hi.jestine..how to check audio toroidal tranfomer with 230v primary input and two sec output.sec side got three wires colour red,black,red and other blue,black,blue..i don know the output voltage ,but filter e cap are 63v 10000uf and 25v 4700uf..becos when i connect these to the main board, the bridge rectifier kbu 804 blow,before that it already blow..can the toroidal tranformer cause the rectifier to blow or tranformer itself break down?need your advice.thanks..urgent.

Hi,

The 63 volt line should have 30 to 35 vac and the 25 volt line should have 10 to 15 vac. If the ac output voltages are within range then the bridge rectifier will not blow. Check also the components after the bridge because if there is components shorted even though the transformer is good the bridge will still blow.

Jestine

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Dear justine,I have found that article to be very valuable. Now I have a question. I wIll try to be breif as possible .Thanks to your excellent book on testing electronic components,I have successfully repaired the power supply  on a stereo amplifier I am working on, and all voltages check normal,however no sound from the speakers. I suspected the muting circuit was the problem, so I tested the voltages per the schematic and found no voltage on pin 4 where voltage should be 13 volts. I removed the two electrolyte capacitors from the circuit for testing. One tests fine on both capacitor testor and analog meter,but the other one tests fine on capaticitor tester but no movement of pointer on analog meter in any range. Capacitor in question is 50v -0.47 mf. My question is, can a capacitor show excellent micro-farad value on capacitor tester and still be defective? Thankyou. sincerely Bob

HI Bob,

Yes i have come across many e-caps that have showed good result and yet failed. You need an ESR meter to test e-caps. You can read this article:

http://www.electronicrepairguide.com/esrmeter.html

Jestine

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Hi Jestine
Anything on Microwave oven repair?

Hi Roger,

Try this link:

http://www.repairfaq.org/sam/micfaq.htm

Jestine
http://www.JestineYong.com

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Dear justine,I have found that article to be very valuable. Now I have a question. I wIll try to be breif as possible .Thanks to your excellent book on testing electronic components,I have successfully repaired the power supply  on a stereo amplifier I am working on, and all voltages check normal,however no sound from the speakers. I suspected the muting circuit was the problem, so I tested the voltages per the schematic and found no voltage on pin 4 where voltage should be 13 volts. I removed the two electrolyte capacitors from the circuit for testing. One tests fine on both capacitor testor and analog meter,but the other one tests fine on capaticitor tester but no movement of pointer on analog meter in any range. Capacitor in question is 50v -0.47 mf. My question is, can a capacitor show excellent micro-farad value on capacitor tester and still be defective? Thankyou. sincerely Bob

HI Bob,

Yes i have came across many e-caps that have showed good result and yet failed. You need an ESR meter to test e-caps.

Jestine

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Hi Gasant,

Perhaps a clarification from you will help me understand.

1)      Is hot transistor and fet the same- they are different even in testing

2)      In the case of hot transistor. The collector is connected to  a flyback pin which has 67v.(pin marked as hy)

Not sure about this tv, usually the collector pin will mark as “C”. This “C” pin have connection with the B+ flyback pin because this is the primary winding of flyback.

3)      Is the collector leg supplying power or receiving- the power is coming from the B+ pin. This means The B+ voltage passes through the primary winding and connect directly to “C” pin.

4)      Where is base getting power from. I trace base to a small 4pin transformer. Base is getting a pulse signal from the horizontal driver transformer. And the driver transformer signal is coming from a driver transistor. And this driver transistor is coming from horizontal oscillator ic.

5)      Emitter seems to be earth. Yes you are right

Regarding the small 4 pin transformer. Is it b+ coil.

It is a horizontal driver transformer.

I looked it up in the book. But info states only 2 pins work. I removed this transformer and wires are connected to the other pins. What can it be.

TV Does not have B+ coil except Monitor. The driver transformer should have one primary winding and one secondary winding.

Jestine

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Hi Naseem,

 

the things is that i don’t know exactly where to check (other than HOT, FBT, Main filter Cap, & STR). and i don’t know what is the power IC in this TV. is it the STR6707?

yes you are right STRS6707 is the power ic.

if you show me where to check and how much, and if not good volgate what components to check, that will be very help full. for example when there is no voltage in the base of HOT what components should i check and where is the source of it.

If you get about 100vdc at the B+ and some 12 and 15 volt then you can presume the power supply is good.

another example is why, there is more voltage in vcc pin of STR6707 then it should be.

It could be that the smps transformer is not energized.

i checked the voltage in FBT pins, in 2 pins of it (other than the one which is connect to Collector of HOT) there is 100+ dc voltage, but in the other pins there is no voltage at all.

When you get 100vdc this mean the power supply is working.

again if help me to understand (for this TV) what voltage should be where and how much, and if it is not normall what components to check, and where is the source of it, that will be very help full

For your information this explanation is a big subject it can’t be explained in a single email. Different TV model have it owns output voltages and have different circuit designs too. I suggest that you get Humphrey’s ebook or get TV repair book from amazon by Homer L Davidson. Humphrey’s ebook comes with photos and his personal support and this will make your life easier when troubleshooting tv. It can cut short your learning curve.

Or you can visit this website below where i have found it to be very good:

http://www.repairfaq.org/samnew/tvfaq.htm

Jestine

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Thank’s for sending a message to me and Thank’s very very much for the Troubleshooting tips and repair. I learn a lot of that book,. i have a problem  sir  when connect vga cable the monitor wil shortdown ? may i get a solution sir

Hi,

You may have to check or replace the eeprom and CPU IC. Before that check if the RGB,H and V line from the VGA to CPU have any leaky components or not.

Jestine

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Dear Jestine Yong,

I have a colour problem with a Acer 17 inch AL!715 model and I need your help.

It came with red colour missing.. The vga cable is connected inside and I  have to  remove the LCD cover to check.  I unplugged the a small connecter with 13 holes. On checking with a meter I found there was no connection from the red pin of the vga connecter (to the pc) to the red socket of the 13 holes  socket.. I had to cut near the connector and found there was no connection from the cut red wire to the red pin.

I checked all the wires to see to which pins they are connected. I  marked them (the pins and colour of the wire that is connected to them in my Book). I got a new connector and soldered the wires back according to my marking.

When I tested it all the colors are there.  But the screen comes on green with the word ACER. The desk top colour has also some green color missing. It is dark in some places. When using it seem ok  but some times the green color is missing in some places .

I hope this problem can be fixed with your expertise.

Thank you very much,
Tana

Hi Tana,

LCD Monitor rarely have color problem. I suspect that the work you have done on soldering of the socket/connector. I suggest that you recheck all the signal wires again. Hope the below link can be a help to you:

http://en.wikipedia.org/wiki/VGA_connector

Keep me update on this.

Jestine

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sir how was day,
sir i was repairing crt television 14inch the problem was that the electrolytic capasitor rated 25v,2200uf at the vartical circuit was getting very hot which course the capasitor to blow out. and i replace it with the some capasitor and within a few minute it get hot againt i remove the capasitor complitly out of the board and i make voltage test i find 25v, replace it againt with 35v,100uf but the tv show a horizontal line.Sir what is the possible solution of this problem, can i replace the vatical i/c? or what shall i do. Thanks

Hi,

If the cap is blown then direct replace the vertical ic. Before that make sure the supply voltage to the vertical IC is within range.

Jestine

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I have a Pensonic 21″ TV with a b+ voltage dropped when switch on especially early morning and the standby led blinks it takes about 30 minutes for the b+ voltage to raise up. After that the tv back to normal.I have changed all the related capacitors at the power section either primary or secondary side but the problem still exist. Thanks

HI Andi,

Have you try to connect a light bulb between the B+ and ground line andsee the voltage. If the voltage is stable and good then the problem is in the high voltage side. Probably a leaky flyback or bad surrounding components. If the voltage is not good then check the power supply section. Keep me update on this.

Jestine

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