Electronics Repair Questions and Testimonials- Part 35
Hi M. Yong,
Few weeks ago I purchase your book "SMPS Repair guide" and I would like to say
a huge thank you It is a real benefit for me to follow a guide to fix most of power supply
on the market. I increased my speed (Save my time !) to analyse and test the smps and save my money in consequence.
Thanks Mr. Yong, I really like these news letters that you always sent. It has over the period of time improve my level of studies and also it has greatly improve my skill of work in my workshop, that my workshop had became the number one in my area.
So thanks for the hard work, may God bless you.
i hope you are well today,
i am just writng to you to give you an update on the amp i was trying to fix,
the resistors turned out to be okay you were correct,
i replaced the following,
TWO/ 3.15AMP FUSES(QUICK BLOW)
FIVE/ SPADE CONNECTERS
TWO/ TIP35C TRANSISTORS
ONE/ MPSA55 TRANSISTOR
TWO/SMD 101 RESISTORS
TWO/AMP ICS TL072CD (as recommended by you)
and im pleased to say the amp is now working,
THANK YOU Jestine for your help
its took me about two years,but i am slowly building up my equipment,and trying to do as you advice through your ebooks and blogs etc,
i have just got to buy your switch mode power supply ebook now when i can afford it,and i think i will have all your books,i normally repair all the different types of game consoles,but the economy is so bad here that i am trying to learn to repair other things as much as i can,how are you finding getting work,where you live,is it a struggle,thank you again,and il be in touch soon with my new adventures in electronics,
what does it mean,a component is shorting another to ground?
Lets take capacitor as an example. If you check with your analog meter the needle will kick up and move back to original position. If this capacitor is shorted this mean the pointer will kick up either way and remain in the low ohm and stays there. This meanif this capacitor is connected between a supply line to ground and if this capacitor shorted it means the component is shorting to ground.
what is IC signature?
Below is the link to typical component signature. It can also be transistor or ic signature:
I am from Eritrea
I am working on an LG Tv board(universal board type) for repair.The problem is when the TV is turned on,the horizontal transistor is hit by an overvoltage.I removed the transistor and measured the voltage at the collector.it reads 220v DC,instead of 90-115V dc.primary side is OK.I replaced transistors and zener diodes at the secondary.Now the collector voltage reads 110V dc.When I turned on the TV,it worked fine for some minutes and the horizontal transistor shot dead again.Collector voltage is 220V dc.Which part of the tv circuit drives the to such a high level out of the power supply regulator circuit?Where could be the problem?
Check the component in the secondary side of optoisolator ic. An increase in resistor value will cause an increase in the B+ voltage. If no bad component, direct replace the opto ic and TL431 and retest.
1.when using voltimeter to test voltage,how many voltage should i expect at the legs of the primary power transformer and which of the pins is the voltage found?
YOU can't test the ac voltage because it is a high pulse ac.Your meter will give a unstable and corrupt reading. test the dc voltage after the secondary output diodes.
2.when testing the voltage of the inverter transformer,should i use ac or dc and what range should i set my analogue meter?
Set your meter to highest range and it is ac.
3. what causes the lcd monitor screen to shut down when the brightness is increase?
power supply itself have problem. When you increase the brightness it will draw more current and if the power supply can't live up to that current (due to the problem in the power supply itself), it will shutdown.
4. what causes the monitor not to turn off and manage to turn off,i refuses to on again untill the power cable is removed and plug again?
It can be the power supply or mainboard problem.
5.in your ebook,i never fully understand the start circuit.i s start circuit the cable connection between the control panel switch and the main boaed or the cable connection between the mainboard and power supply board or just tell me the exact place it is found and how i will know it.pls explain it better than your ebook?
Start circuit has nothing to do with the control or cable connection. Start circuit got the 12 volt supply but can't channel to the inverter ic because it has to wait for ON signal from the MCU.Once the MCU sends out the ON signal then only the start circuit conduct and allow the 12 volt supply to the inverter ic.
6.if the power led is on and no display,can i say the start circuit is working?
Start circuit working is when you see 12 volt measured in the vcc pin of inverter ic. It can be 12v, 14 v, 5 volt and etc and depending on the model.
Thanks for your hardworking for sending us your monthtly newsletter. Sir i have a crt panasonic television 26inch on my bech i think the problem of this tv is on power supply, the problem is that when you turn it on the voltage at the secondry side will disappair in few second. I have use dommy load to test the power supply, when i turn the the power on the bold will light up in few second and goes off. I test the resistors located at the primary side but i will not find the the problem, so i decided to tell you to get your helf. Thanks
If this tv is using optoic and tl431 ic please do direct replace these ic and retest and also check the surrounding components especially resistors on the secondary side of optoisolator ic .
First of all i want to thanks to your e-books i have a lot of learn about power supply and lcd monitor Repair. for now i'm starting to apply to repair a lcd monitor since before no have me idea to repair lcd monitor but when i read your e-book LCD Monitor easy to understand not like the other book. sir, i have a question regarding the CTX LCD Monitor have problem in power supply when i test the voltage output 5v ok but 12v no have i try to check the primary filter capacitor, Bridge Rectifier, Power IC, Non Polar cap, and SMP Transformer all is good then when i swictch the power supply i heard the sound like tik tik tik like that. sorry my english hope if not clear.
Thanks for the support on my ebook. You mentioned that there are 5 volt output but 12 volt is zero. I just want to know if the 12 volt coming out from the schottky diode or from a voltage regulator ic?
If the 12 volt is coming out from a schottky diode this meanthe schottky diode could have open circuit bad filter cap along the 12 volt line an open secondary winding in transformer which is very rare or the load have something shorted causing the 12 volt to drop to zero.
Try remove componenrt along the 12 volt line or cut off the 12 volt line from reaching the inverter board. this way you can isolate to see if the power supply problem or the inverter board have problem.
Hello sir. Please i need your helps . 1 – i have one LG TV 21FU6TL SQUARE TUBE .the problems is in horizontal circuit . If i on this tv it will not full in both sides . I open it , i can see some coil around the fly back which was burn , and EW IC TDA8145 with one transistor beside it A1659H was also burn , i change all these components but still it not full , the raster is in middle , and i notice that this A1659H is too hot , the output of this IC TDA8145 was connected to base of this transistor . Help me .
The only thing you can do is to check all the components corresponding to the burn component. there must be some other components that had gone bad. Make sure the transistor collector pin have about 10 to 20 volt.
2 . I have one hitachi tv C2114TE , if i on this tv the fly back will spark , and it will cutoff some times it may show and still sparking. i suggest that the fly back was damaged , i now change it, but it do the same thing , i now remove the yoke wire , it not spark , i change the yoke . And it still sparking again . Now the problems is now 2 . Because now the color not bright anymore , it dull in picture
Sparking can be due to:
B+ voltage too high causing the high voltage to "Jump out" or arc over to nearby part. Make sure the B+ voltage is according to the TV spec.
Tv Is Going to Stand By Mode After 10 sec.No output voltage from the Power supply.if i want i can on it again but it goes same thing happen Again .
This means the CPU or eeprom could have trigger the standby mode. Make sure the supply voltage to both the ics are good and the cpu crystal have sine wave. If the voltage and signal check to be good you may need to replace the cpu and eeprom and retest. Before that make sure the remote control is not pointing to the tv. Sometimes a bad remote control could cause such problem.
i need your help on some problems i am having in the attachment i send, this type of power supply get bad very bad easly it is suppose to be given 47v dc and very often i am getting a lower voltage such as 27v dc. can you tell me which component could be possibe going bad?
Lower voltage than normal can be due to:
testing the power supply without connecting to the mainboard /load
bad low ohms resistor in the primary side.
Bad filter cap in the primary and secondary side
Bad optoisolator ic or even tl431 ic.
I have a Scientific Atlanta Explorer 3200 cable TV digital terminal which is totally dead. When I opened it, I immediately noticed that the power supply main fuse was blown. So, I removed the power supply from the device to have a closer look at it and I saw some burnt marks around the solder joints for two of the four diodes of the bridge rectifier. I tested the main fuse socket with a 100 watts light bulb and it lits like the sun. So, the problem is definitely not just the fuse. So, I removed and tested the main filter capacitor's capacitance and resistance. Both (capacitance and resistance) tests returned good results.
After having reinstalled the main filter capacitor and replaced the fuse and all four diodes of the bridge rectifier, and make sure that the 100 watts light bulb does not lit when connected across the main fuse socket, I checked the voltage across the main filter capacitor and the power IC VCC pin (see IMAGE-A for tests results). About the power IC (ICE 2A265), according to its datasheet, the VCC pin should be between 8.5 VDC and 21 VDC. So, at 12.5 VDC, I guess it is correct. What do you think?
Yes it should be ok to run on that voltage.
I also checked the voltage coming in and out of the transformer (see IMAGE-A). What I'm not sure is if I should use the cold or hot ground. As you can see from IMAGE-A, only two pins have input voltage reading. As for the output voltage, using the cold ground I get no voltage at all, but using the hot ground I get a 58 VDC on all pins. So, what is the right voltage test for a transformer, using the cold or hot ground?
Is the transformer's input and output voltages look normal?
Should I keep investigating on the primary or the secondary side of the transformer?
Which particular component do you suggest to check?
Thanks for having taken the time to read.
In your case, since the bridge diode already shorted this mean there is chances the power ic may have kaput. Try check all the components in the primary side which include the optoisolator ic. If all check to be good direct replace the ic and retest. Check also for shorted secondary output diodes.
By the way you are not recommended to test on the transformer output pin because they are high pulse ac voltage which your meter can't support it. measure the dc voltage after the secondary output diodes with the black probe to cold ground. If you get dc voltage this means the transformer ad the primary is working. If you get zero volt this mean there is problem in the primary side.
Hope you're fine upon reading this letter of mine.As
usual i have another question about repairing lcd monitor.It is about
the lcd monitor HANNS.G HW191D it's 19'' lcd i'm not sure if you're
familiar this kind of brand.The problem i was encounter about this lcd
is that when power on the monitor the power led lit but there was no
display on the monitor about 2-3 seconds the lcd suddenly shutdown
then with in 2 seconds the monitor start automatically on its own.I
did measure the standby 5volts found unstable in sequence with the
power led on 'n off state.I try to disconnect the connector from the
main and measure again the standby 5volts found stable.I was
suspecting that the main board was the problemt.Am i right jestine
that the culprit is the main board?how does the main board act as
start up cicuit?what particular chips or ic involve the
operation?..Hoping that in your hectic schedule you maybe able to
share solution regarding this problem..
Thanks and more power to you..
First you need to make sure the output from the power supply are good and stable. Next you need to make sure the output from the voltage regulator ICs in the main board are good too such as 2.5 v or 3.3 volt. If the voltage is good then chances is high the MCU chip in the main board have problem.
I would like to thank you for your books.Since I had them I have gained confident on my pratical skills.
I know I said it before but It is coming from the bottom of my heart.I can tell it is the best investment ever.
You need to know that to be blessed by my GOD.
You are trully a good man.
Hi Sir Jestine,
Good Day Sir.
It's been a long time sir i did not email you about the problem that i encountered in my repair field. this time sir i'm gonna need your help again.
Sir friend of mind bring his Dell LCD monitor at home, its dead set sir, the fuse is blow sir. In my experience i already know that the power transistor got shorted, so i'll just replace the transistor and it will power up again. So i told my friend to buy the transistor, after he buy the transistor i installed it right away and change the fuse and power it up right away. the monitor get back to life, but after few seconds the monitor is back to dead set again. i've check the rectifier diode and it check find. and also look for swollen capacitors, i'de replace 3 bulky capacitor already. all other capacitor look okey and i didn't mind to check time. Sir what i know is if the power transistor got shorted again, meaning their is a bad output capacitor or bad output diode in the circuit. i'd check them already and it tested good. Sir pls help the transistor keep on blowing. i dont know what to do.
Thank you so much sir and God bless.
Gil Labis Jr.
If the transistor is shorted you may need to direct replace the power ic and check all the primary side for some other bad component. If there is a a one low ohm resistor (0.22 to 0.47ohm resistor then direct replace it.
Hi Mr Yong, its Lwazi here in RSA. I would like to thank you so much for yo help when i needed it the most. Its about the part number STK 396-130. The web address u sent me realy helped a lot, i got the ic and it worked so well that the tv is now working again. Thank you very much, i appreciate. Thank u for the monthly newsletter that u send me. Thank you again. Lwazi Malisa
One of my users tells me her flat screen monitor, Dell E196FPB has issue. What is happening is every few minutes the monitor will show that her 'workstation is locked'. She needs to enter her password to get back to desktop. At first I think the PC is the issue but PC checked out fine. I put a known good monitor on her PC and now all is well. This leads me to suspect the monitor ? Could the monitor cause the PC to go to 'workstation is locked' every few minutes. As I said installed new LCD and issue resolved.
I've not seen a monitor that can cause the workstation to "lock". Try take the monitor and run from other pc and if the problem still the same then the monitor itself have problem. You may have to check if there is any stuck front button that could cause it to lock.
Message: Thanks a lot for the great advice. My RCA model F36650 gave out on me the other day and I found out that I'm going to need to replace my HOT-transistor and the high voltage transformer. I already removed the circuit board and unsoldered both the transistor and the transformer. All I need to do is find repalcement parts. I'm taking everything you wrote to heart; I'm looking for a C5148 transistor. I've noticed that some of the C5148 transistors have different writing on the bottom of the model number, for example the one you show reads 8:K, others show 6:H etc.. however mine reads 3D. What does this mean? and do I have to take it into account when replacing my C5148? Do I need to find a replacement model that reads C5148 3D of can I use one of the others ones i.e. C5148, 8:K or 6:H.
I suggest that you visit the link below:
As for the part number if you could find C5148 this mean you could use the part and no need to look for the bottome number.