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Electronics Repair Questions/Answers and Testimonials -Part 66

By Jestine Yong on October 23, 2010

Hello Mr Yong

Sincerely speaking, you are a sort of genious. With your books, for the very first time, I’ve discovered a real course of electronic repair practice. No useless gossiping, each of books is a rich goldmine for every technician young or not.

G R PONTY

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Hi Jestine,
Your LCD monitor repair book is excellent.

Best regards,
Nikola

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hi jestine,
thanks for your resource materials, you have really added value to my skills. i really appreciate.

Wilson

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I have a Vintron 14 Inch colour monitor. There was a problem with metal dust getting inside the monitor. I found that MOSFET 6N60 and SMPS controller UC3842 were damaged. I replaced them and the monitor now turn on without problem. But as soon as there is data signal from the computer, the orange light too turns off. Please let me know where should I check.

Thanks,

HI Sumod,

If the output voltages from the SMPS are good and stable and the CPU is receiving 5 volt then suspect a bad CPU.

Jestine

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Hello Jestine, here are the attached images, what is this? Is it a type of diode setup you’ve seen before?
It is from a automobile security alarm system

Thanks, Nick

HI Nick,

It has similar setup (connection) like a schottky diode except that each diode is pointing the opposite way. Schottky diode have two diodes pointing to the same direction and mostly found in the power supply secondary section. You can use an analog meter to test each diode to see if it good or bad. I’m not sure about automobile circuit but if there is AC enter the center pin you can expect DC voltage at both sides of the pins.

Jestine

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HI Beh,

refer to your fifth book how to make your own blur buster. section of the book
I understand that:
1- i have to find a good fbt from my salvage parts

Yes.

2- i have to cut all the pins and must be cover with the epoxy glue not flammable

Yes.

3-i have to solder to pro par wire and must be solder to ground of the fbt and also must be covered with tape
and solder to good ground of the board

Yes.

4- i have to make another hole in my high voltage cap and send my second high voltage wire that is coming from my buster in to it and must be arc free

Yes.

5- i have to place this blur buster some where near convergence board of the tv or monitor
am i right and this fbt will work as buster of monitor?

Yes you are right!

Jestine

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Mr. Young

I have a question regarding lg 47lg70- ug

I have no backlights – working voltage is correct going to backlight inverter boards have gone thru the trouble shoot service manual – there is a picture and sound just back light inverters not turning on

Any insights

Thanks Allen

HI Allen,

If there is supply voltage to the inverter ic and no output waveform to the high voltage transformer then suspect a bad inverter ic or bad corresponding components.

Jestine

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Hi Jestine ,

On page 8 you say that the knob on the voltage supply must be slowly increased and watch the current draw. I want to know what is the maximum voltage I should use before that bad component starts to get hot. For example, if VCC is 5V on that part of the circuit , turn the voltage up to say 2.5V or 3V ?

Watniegh Chang

HI Watneigh,

It depends on how severe is the short circuit is. Sometimes when it reach one point something volt, you could see the current consumption already shot up!

Jestine

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Hi S,

Many, many thanks for confirming my understandings. Now, I feel very more comfortable to test and interpret ESR results.

You are welcome!

So, I retested again all the removed e-caps (from the motherboard) and again I stumbled on an e-cap that I’m not sure if it is good or not. This time it’s the ohm results that are not so clear. This e-cap is a 330µF @ 25v, rated at 0.26 (based on the chart and on how you told me to calculate an uncharted value). First, I tested it (off-board) with my ESR meter and it returns a 0.05 ohm. Could be good, but because it looks a bit low, I decided to test it with an analog multimeter (just as you suggested in your last reply). So, to confirm its state, I took my analog multimeter (which looks pretty much like the one that appears in your books’ photos), set the Ohm range to X1, made the tests (both ways), then to X10 and made the tests again (both ways). At that point, I was still not sure and a bit confused about the results. So, I got back to your books and read again page 98 and 99, from your book “Testing Electronics Components”, and also page 91, from your book “LCD Monitor Repair” (about SMD capacitors). If I understand correctly what you clearly said in those books (about testing capacitors with an analog multimeter in the Ohm range), no reading (needle staying at infinity – with test probes both ways) means the capacitor is shorted.

No reading when tested both ways means it is open. It depends on the value you are checking. If the microfarad is big you will see that the needle will kick up and then gradually go down very fast to infinity and this cap is good.

If there is a charge and a discharge (needle flicks up and down to infinity – with test probes both ways) it means the capacitor is good.

Not 100% because you still need to test the ESR value and the value of the capacitor capacitance.

Finally, if there is a steady ohm reading (needle staying away from infinity – with test probes both ways or not) it means the capacitor is bad.

If you set to x 1 ohm and both ways show that it stay at low ohm then the cap is shorted.

But, the e-cap I tested (the 330µF @ 25v e-cap) did not yield results as clear as what I described and I cannot clearly and without any doubt interpret those results (see “E-Cap_Ohm_Data.pdf”).

If my understandings are correct, three tests tell me that the capacitor is good, but a fourth one (where it stays at 750 ohms) tells me that the capacitor could be bad. Which test should I believe? Can you enlighten my understanding of how to correctly interpret results from a ohm test using an analog multimeter with (what looks like – to me) ambiguous results?

Actually it was confusing to use the analog meter to find out the overall health of a capacitor. What we can do with the analog meter is to confirm that it have no short circuit. If it can charge and discharge then we know it has no short circuit and we proceed to test it with esr meter or digital capacitance meter.

Also, I have a question about ESR meter versus multimeter in Ohm range. With an ESR meter, based on a given “normal” value, a lower ohm reading (than normal – excluding 0.01 or 0.00) means just enough (or low) resistance and a high ohm reading (than normal) means too much (or high) resistance. Now, I know we cannot test ESR with an analog multimeter (that’s why ESR meter exists) but, is the needle position of an analog multimeter in Ohm range can be interpreted the same way as the needle position of an ESR meter,

I mean the more the needle goes away from the infinity (lower ohm) less resistance the e-cap have and the more the needle is near the infinity (higher ohm) more resistance the e-cap have, or is it the opposite?

No both meters reads the ohm value differently. The ohm value that we got when we check on capacitor using analog meter does not represent how good the capacitor is. But for ESR meter, the ohm value that we get is very significant to know if the cap is bad, marginal or good.

Jestine

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HI Kelly,

From the photo, it seems that there is one standby power supply and another one was Main power supply. When you get the 5 volt, this means the standby power supply is working. When you did not get the 12 and 24 volt, i believe the main power supply is not running. In order for the main power supply to work one of the optoisolator IC must get a On signal from a source and this source could be the motherboard.

Did you connect the power supply to the motherboard? The CPU in the motherboard will first receive the 5 volt and then it sill send a signal to the optoisolator ic to trigger the main power supply so that you will get the full output voltage of 12 and 24 volt. Bad optoisolator IC, corresponding components and bad CPU will cause the main power supply not to work. You have to check on these circuits or components. It could also bad components in the primary side of main power supply.

Jestine

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Hi Alex,

Thank you for your newsletter.

You are welcome!

By the way, Where can I get the circuit of opto isolator IC?

From any diagram that you can download from the internet. If you need the spec then you may need to visit this link of datasheet to look for it.

https://www.jestineyong.com/?cat=61

Actually, I am looking for optoisolator P520, P521 & P620 which are used in servo amplifier for CNC machine.

P stands for TLP520, TLP 521 and TLP 620.

http://www.alldatasheet.com/view.jsp?Searchword=TLP521

And can you recommend some book on servo amplifier especially in troubleshooting.

Sorry, i have not across such book. May be you can try search it from amazon.com

Have a good day!

Jestine

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HI Eric,

i Jestine, How are you ? Hope all is well with you and your family.

I’m fine thank you.

My Monitor has gone down. Whenever i power up my computer the monitor keeps going on and off by itself. there is a click from the relay the power light comes on but then it goes away. i connected it to the isolation transformer but when i press the power button it continues to make this clicking sound from the relay and pulls the voltage meter on the isolation transformer to zero . What is causing this behaviour ? is the relay bad ? or some other component has gone bad. I need you help on where to begin in order to locate this problem Thanks. (the power light keeps changing form orange to green, green to orange continuously).
Thank you.

If the output voltage from the smps are good and stable then suspect a bad CPU or bad eeprom ic data. The relay signal is coming from a transistor that triggered by the CPU signal. If this CPU produce a continuous high and low signal thus your relay will click. Make sure also no shorted components in the high voltage area.

Jestine

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Dear Sir,

Good evening. Hope you are fine. I have one question about ATX SMPS is that it is working in some motherboard but in some other motherboard it do not start. I have measured the output voltages and found all voltages are ok. But in place of -12v I am getting -10.3v. I have changed the filter capacitor related to this voltage but the voltage is same. My question is what it may be the problem whether it is smps transformer problem or something else.

Thanking you

HI Gopal,

Try replace the big round coil if all other components have checked to be good.

Jestine

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HI Frank,

It looks like I need to get some funds together for the other equipment before I buy your ebook.

No problem. Equipment is very helpful in speeding up our repair job.

– I have a cheap voltmeter but no capacitance reading
– need a digital capacitance meter – do you have any recommendations? range of capacitance?

Try buy this model TES 1500 Digital capacitance meter.

– Blue ESR tester – I think I can borrow one from a neighbor. If not, I’ll have to purchase.

You need this meter because this meter had helped me solve lots of repair problems.

– Blue Ring tester – not sure what this is and what it tests. Is it to test transformers?

Yes, it test coils like transformer, B+ coil, flyback and crt yoke coils.

– isolation transformer – I think I know where I can purchase two identical (120VAC to ?) transformers to make one. I couldn’t believe how expensive they were.

Jestine

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Hi Muhammad,

Hi.Thank you for yours repay ,this type of power supply we are only reapir in this country,i dont have any diagrame or trouble shooting chart,Just experience and hit and trail the main problem in usualy in control card !which consist several coupler you can not check voltage inside just cold test what yours advised?

If you would like to make a certain test i suggest that you solder with wires on the few testing points.

Do you have any article about soldering technique?i want to increased my knowledge about soldering.

Try search from youtube .com and you could see lots of video on soldering techniques.

Jestine

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Sir,
I found in a monitor 2200mf/10v capacitor and 470mf/16v, both 105 degree are bulged, can i replace them by 2200mf/50v and 470mf/50v and 85 degree .
Thank you sir.

HI Uday,

You can use the 85 degree cap but the working voltage is too high (50v). Find one that is rated 25 volt and it should be good because it is cheaper and have the space as compare to the 50 volt that is expensive and consume more space.

Jestine

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Hi Jestine,
I have another question about H/V ic of crt Tv how can be determine if it is defefective or not,how can get voltage mesurement out put of vertical and hozontal..thanks nilo..

HI Nilo,

The best to determine if the ic is good or bad is to use scope. If there is supply voltage but no proper output waveform then suspect the ic or corresponding components have problem.

Jestine

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Hi Jestine!
What tools do use to Desolder components from double sided boards?
I’m having difficulty with this!
Regards
Riaan

HI Riaan,

Usually i just use my normal hakko 981 gun and a desoldering pump to do the job. It require patience and take sometime. If you want to do it fast you can invest on this tool:

http://www.mcmelectronics.com/product/HAKKO-P808KIT-/94-410

Jestine

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HI Anand,

Is ther a different between a flyback of a t.v and a monitor (p.C.)

Yes, the monitor flyback have internal capacitor and tv flyback do not have it.

How can a test a flybackt of a t.v. with the ringtester.

Please visit this website:

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

How many winding does a t.v. flyback has.

Generally it has one primary winding and few secondary windings.

And how tot test all those winding.

For testing primary winding you can visit the link above. Since the secondary winding rarely have problem thus we do not test it. Blue ring tester can’t be used to check on secondary winding because the inductance value is too low. We can only use ohm meter to check and make sure the winding does not short to other windings.

Jestine

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Hi Jestine,

I have today purchased your Testing Electronic Components book and am very impressed with it and the extra reports.

Best regards,

Andy

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HI Simon,

The best is to use back the same type as certain monitor will cause the HOT to run hot and blow after sometimes.

Jestine
http://www.JestineYong.com

Hi Jestine,

Is it advisable to replace an A-type HOT with a

D-type HOT.

Regards

Molefi

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HI James,

thanks for the information on switch mode power supply.its so useful and informative i also like the simple way you use to explain it.

You are welcome!

Please help me with this,i have noticed that in some switch mode power supplies especially on the CRT TVs, i have seen this on some Tedelex tv’s that at the power supply it commonly uses BU508A,the heat sink where this transistor is mounted will over heat and later the transistor will blow,my question is what causes the over heat

The base drive signal to the transistor have problem. Make sure the corresponding components are good especially the electrolytic capacitor. Please visit this link that can shed some light for you:

https://www.jestineyong.com/?p=403

Have a good day!

Jestine

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HI Roger,

sir,now the tester is working well,i tried to check a 2.4 and 10 v zener,now it register ok to the meter

Congratulation.

,,,,by way,im preparing the second tester,pwm ic to assemble,,,,this two tester is package in one repurbish ups box,,i put only one 12 0 12 transformer,,to supply the two tester,,,and im using a single pole,douple throw sw.2 pcs,,,,when i sw.on in up position,the zener tester will operate,,while the pwm-ic is in off position,,, and when i sw.down the pwm-ic will operate,,and the zener is in off positon,,,thanks sir,,,god bless..,

Not bad, you have a creative ideas! God bless you too.

Jestine

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Hello Jestine,

I’ve already downloaded the ebook, Testing Electronics Components. Your book is great and direct to the point, it’s practical. I’ve already read several electronics book but yours is different, it’s well explained. Thanks a lot for sharing your knowledge.

Regards,

Barnar

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HI Sumod,

Thanks Jestine for the information you provided.

You are welcome!

I de-soldered the output terminals of the SMPS transformer and powered up the Monitor. I saw the power indicator light still turned on. I checked the voltages on the transformer terminal and found that for all the required voltages of 7V, 24V, 60V, 90V, +12V and -12V against the ground, I could get only two voltages on the terminals. Either it was 14V or it was 34V amongst all the terminals. I wanted to know if I should solder back the terminals and again check the voltages. I suspect that I am not going to see any major change.

Now, if I believe that SMPS voltages are a problem, what do you think must be my next action?

It seems that the output voltages from the SMPS are good. If the CPU is receiving 5 volt and the VGA signal cable is connected (no broken horizontal and vertical wire internally) then suspect a bad CPU or EEprom data had corrupted.

Jestine

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HI S,

I hope that you can read this message before answering my last reply (included in this message) because I just found that I totally misinterpreted and misunderstood what you said in your last reply (also included in this message).

In your last reply, when you said: “No reading when tested both ways means it is open.”

Yes.

I implicitly interpreted “open” as a “good” (or normal) condition for an e-cap. This was a BIG ERROR from my part. Since I had no idea about what is an “open” capacitor, I tried to find the answer in your books without any luck. I was so much into your books that I totally forgot that I also have the Bernard Grob’s Basic Electronics book (which you recommended to me – thanks to you).

You are welcome.

So, I started to search this book about the “open” capacitor’s state, then BOOM! I stumbled on chapter 20: “Capacitance”. All the information about capacitors is there, in plain black on white. Now, I know what’s an “open” capacitor’s state (and it’s NOT a “good” – or normal – state).

You are right!

Here’s my all new understandings about capacitor’s tests and the different possible results (indicating the capacitor’s current state) using an Ohm meter (I hope that I get it right this time).

If the capacitor is charging correctly (needle goes away from infinity, up to a very low or 0 ohm, then goes back to infinity – with test probes both ways), it means the capacitor is in a normal state.

Yes.

From that point, if the ESR and the capacitance tests also return a normal state, then the e-cap is good.

Yes

If the needle goes away from infinity, up to a very low or 0 ohm, then goes back and stays away from infinity (with test probes both ways), it means that the capacitor is in a leak state.

Not really, it depends on what value of capacitor you are testing. There are many good capacitors acting this way that’s why i do not use ohm meter to test capacitor. It was very confusing.

If the needle remains at infinity (no reading or very high ohm – with test probes both ways or not), it means that the capacitor has developed an open state.

Yes, if the capacitor value is big (may be more than 1 uf) and if you have set your meter to x 10 k ohm

If the needle goes straight (and remains) at 0 ohm (or at a very low ohm), it means that the capacitor is shorted.

Yes you are right!

Do I get it right (this time)?

Yes you are absolutely correct.

But, as you said in your last reply, no matter what’s the result of the ohm test, the global health of a capacitor can ONLY be confirmed after having made the ESR and the capacitance tests. Right?

Yes and one more test which is the insulation test but it apply only to bigger voltage of capacitor.

Jestine

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Hi Jestine,

Seeking your expert advice on the possible causes of this symptom.

I have replaced the Vertical IC (TDA 9302A) & HV IC (TDA 9115) with No improvment. Also have testing the surrounding components of the Vertical IC but did not find any faulty component.

Thank you in-advance.

HI Tang,

Try direct replace the non polar cap in the vertical area as some will test good but fail when under load. Make sure also the supply voltage is good (some vertical IC have positive and negative supply).

Jestine

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HI James,

Hi Jestine , how are you hope you doing well Jestine,

I’m fine thank you.

anyway to flyback transformer repair its possible ?

It depends what is the problem. If the primary winding shorted then it can’t be repaired. If the internal capacitor shorted (referring to flyback Monitor) then it can be refurbished.

or jest replace only to the new, have a nice day Thanks James

New one is hard to get and expensive. If you can get a new one then yes you may replace it.

Jestine

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Hi Jestine:

When troubleshooting circuits with an external power supply, what type of current readings should I get? Hi? Low? No current? Etc.?

Trying to figure out these readings. Thanks…

HI C,

It depends on the equipment current consumption. For example a CRT 14″ Monitor current consumption is 0.3 ampere and if you get 0.8 ampere then you know there must be something that have shorted.

Jestine

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HI Fahmy,

This time I have 1 question regarding component Inductor with body marking YDD 18µH and located near to the Vertical IC. Infact I have doubt on this inductor due to while performing test with blue ring tester the result is no LED lights up, I’ve tried to use the multimeter with resistance test and the pointer kick up. Anyhow when I check the component physical found that there is a magnet and magnetic field on top of the component. Is this a special type of inductor and what is the proper way to check/test this component?. Really appreciate and thanks if you can advised on this matter.

Since this inductor value is small thus the blue ring tester can’t be used to test it. A ohm meter test is adequate or you can get an inductance meter to check the value. Chances for it to go short circuit is very slim.

Jestine

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HI Norraimi,

1. SAYA INGIN BERTANYA…..JIKA SMD RESISTOR TELAH ROSAK…BOLEHKAH IA DIGANTIKAN DENGAN RESISTOR BIASA TETAPI NILAI YG SAMA..?

Ya boleh.

CONTOHNYA : SMD RESISTOR (ROSAK) : 102
RESISTOR BIASA (GANTI) : 1000 OHM.

2. SY ADA SATU LCD MONITOR YG ROSAK…..SETELAH DIPERIKSA..SY DAPATI ADA SMD RESISTOR YG ROSAK (NO. HAMPIR HILANG). SY LIHAT SEPERTI 102 ATAU 103. BAGAIMANA UNTUK SY TAHU NILAI SEBENARNYA….ATAU SY BOLEH CUBA PASANG YG MANA DAHULU…? SY TIADA SERVICE MANUAL UTK RUJUKAN. JENAMA HP, MODEL W1907.

Anda pasang nilai yg tinggi dahulu. Sekiranya ia tidak berfungsi baru letak nilai yg seterusnya.

Jestine

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Hi Jestine,
Can you please help provide me the equivalent parts for 2SK2224.Tks.

Regards,
Chee

HI Chee,

From my databook, the equivalent part numbers are 2SK1463, 2SK1683, 2SK1859, 2SK2147.

Jestine

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salut
_connecteur rètro-eclairage est ce que c’est les 2 fiches cn753 et cn 752 qui ont 2 fil 1 blanc et l’autre rose si oui ya pas de tention; j’ai trouvè que 20vac.
_au pin 9 du ic 751 (tl1451acn) j’ai trouvè que 0.2 v dc
_le transistor a733 pnp, et c945 npn sont en bon etat ainssi que le fus 2a est bon
excusez moi pour le derrangement merci

Salut.

Dans ce cas, le MCU de la carte mère avez un problème, car il ne peut pas envoyer sur le signal pour déclencher le circuit de démarrage. Si le circuit de démarrage ne fonctionnent pas du 12 volts ne s’appliquerait pas à l’IC inverseur tl1451n.

Jestine

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i have a plasma tv model ps50a457p1d.the fault is it has a faint horizontal line at the middle of the screen but through it u can still see the image.the whole screen is full but just the faint line.

Hi Festus,

The y drive upper or the lower board may have problem. Try check if there is any burnt IC or broken track.

Jestine

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HI Jim,

Hope u doing good in god’s grace.

Thanks and I’m fine.

Here’s my questions waiting for u r answers:

1. will a defective LOT makes a resistor in the B+ line blows off when a monitor is powered up(Dell monitor with Acer chassis).?

Yes if the primary winding, internal capacitor or the HOT shorted.

2. what will happen when we rewind different thickness/length coil in a B+ core.?

Increase in B+ voltage. You need to rewind that have the same length and thickness

3. what is the difference between IRF630 & IRF630MF..? can v replace IRF630MF with IRF630..?

Yes both can be replacable.

Jestine

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HI Navneet,

I’ve one vestel psu for lcd tv to repair 17PW15-8. After few second operation the TV is going in standby mode and then again try to comeup (sound and picture appears) then goes again in standby and so onnnnn.

I chilled the IC 807 (SG 3525A) with cold spray, so long cold effect is there the TV function is normal. As the temperature of the IC rises it goes again in the same on and off cycle. During operation I’ve measured the temp.after 17°c it behave like this. I sprayed again to chill the IC It has worked for long period at low temp. I changed the IC but there is no effect. I’ve checked the elctrolyt cond. with esr meter changed all badones with new. Can you please give me some clue?

I believe it could be cause by bad corresponding components. If possible spray only on the components beside the IC and see if there is any changes or not. Make sure that you cover the IC with a paper or plastic.

Jestine

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2 Comments

supreeth

February 13, 2012 at 3:56 pm

how to select resistor value inTLP620

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admin

February 13, 2012 at 8:05 pm

HI Supreeth,

Could you elaborate?

Jestine

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