Electronics Repair Questions/Answers and Testimonials- Part 81
1.LCD MONITOR HP MODEL 1702 (no display )
i’m check all the capacitor look no problem.
First is all the output voltages from the power supply good and stable? Did the inverter ic get the supply voltage?
2.LCD MONITOR DELL E193FPc (Dsipplay off affter few second)
One of the backlight bad could cause display to shutdown. Make sure the output voltages are good and stable and no dry joints in the high voltage transformer.
Are you meaning to say that even the yoke coil checked OK with the blue ring tester ( horizontal 8 rings; vertical 2-3 rings ), there is still a chance that the yoke coil has another problem causing the spark to the picture aquadaq?
Yes but this kind of condition is very rare. I have seen only few tubes with this kind of problem after so many years in the repair line.
Another question is about the logo of an IC labelled as IC1006 in the photo attached. To know the code&marking better of a semiconductor device one should know the maker of it. Do you know the brand / make of this logo. This IC is from the mainboard of a 19" Samsung LCD TV.
Sorry i do not know the manufacturer. Nowadays there are so many type of LOGO’s in the market. The above part seems to be a 3.3 volt voltage regulator.
2 days after returning the set to the owner, he brought back the set with exactly the same problem. Then I tried to replace the white optocoupler near the 78L05 regulator IC, and the monitor works normal again, so far so good.
The type of the white optocoupler was from rarely used one, and I replaced it with PC123.
Good to hear that it is working now.
Hi Jestine,i would like to know what do yo mean by COLD GROUND in your Testing electonic component book.
Cold ground is the earth ground in the secondary side of power supply. Whenever you want to check the voltage at the secondary side you need to connect the black probe to cold ground and the red probe to the supply.
And one thing i would like to know .I have a laminating machine which is over heating when switch mode is on cold you got an idea what cause the element to heat up on cold.
I have not repair such machine before but from your description it seems that there was a signal that had trigger the heating element circuit and you need to locate where the signal was from? If you have the schematic then your job will be much easier to locate the problem.
Thank you for your help with this problem.
I am confused about the problem and the results I am getting.
If I got the 120V at HOT Collector but the voltages were low and then when I put the light bulb in place of the HOT and the light bulb lit up and the low voltages jumped up to about a volt or two above normal what is that telling me? Is that saying the PS is working OK but there is a problem in the HOT circuit?
Different model have different B+ voltage. If the B+ voltage is 120 and after putting in the light bulb you got about 125 volt then it is normal and the power supply is working. The reason we use light bulb is to isolate which circuit that have problem. If the + is only 70 volt and after placing in the light bulb and you got 120volt then this indicates the high voltage area have problem and not the power supply. If after putting in the light bulb the voltage still 70 volt then the problem is in the power supply side.
I was not getting any drive signal from the HOT driver transistor but I think that was because the IC’s or a circuit related to the IC’s was not getting enough voltage to generate everything for the correct output.
Notes. Yes the h/v ic must first get a good supply voltage before it can generate a pulse to HOT.
hi jestine how r u ,hope fine.
I’m fine thank you.
1.there is a capacitor and resistor connected between hot ground and cold ground .why?
To reduce the main interference
2.to measure the backlight connector ac voltage by analog meter,which range we have to select?
select to the highest.
3.in smps ,a smpt have 4 legs in primary.one goes to +of filter cap and another to drain of fet.another to connections are for what?
For feedback or dc voltage to power ic.
in a mobile charger(old type) smps,primary winding
have only two pins?can u pls explain why some have 4 pins and some have 2 in primary?
2 pins no feedback
4.i have built a lopt tester designed by bob parker.
a.i connected the test leads to primary of smpt of a working smps, it shows 6 leds.when i shorted a diode in secondary only 2 leds are glowing.this shows that secondary line is good.by this test i want to know tester is good or bad?or still have faults?
Most of the flyback tester tested on smps transformer will show 4 to 8 LEDs and thus your tester is good.
b.pls tell me the component so that all leds should glow ,when i tested.
Try check the primary winding of a 14/15 " monitor flyback.
c.what shold be the maximum length of test leads?
For this tester it should be about 30 to 40cm
can i put a multimeter test leads for hot collector and cold ground?
No you can’t because HOT collector have more than 1000 volt.
d.if its good ballast choke minimum how many led"s must glow?
2 to 3 Leds
Thankyou so much for your valuable information regarding electronical components .As I am into this field so this information will help me in repairing equipments that will give better service .
As per now I am in need of a circuit map of HP CRT monitor D8896.I have problems with the EHT section. The transistor BU2520 is blowing everytime it is being fixed.Ihave checked all the surrounding components conected to the horizontal section.
Sorry i do not carry any schematic. Try check this link:
Equivalent of c3866?
From my databook the equivalent number are:
2sc3559, 2sc4303, 2sc4517 and 2sc4908
I read one of your articles recipient that checking of integrated circuit can be obtain through the help from oscilloscope.Is it possible also to check using multimeter tester and how accurate the result compare the oscilloscope test equipment?
Oscilloscope is much more accurate in checking a waveform then multimeter. Multimeter can’t be used to test on such circuit.
2.What is the best test equipment that can perform to measure electronics components accurately?
Different components needs different meter to test it. For example Blue ESR meter for electrolytic capacitors and etc. There is no best test equipment.
3. Can we check the capacitor while it is operating using the oscilloscope?
Yes but you must know what type of signal is in the cap pins
4.How many electronics components that oscilloscope can possibly be used to check?
Usually scope is design to check on a circuit and not on a single component.
5.I heard about Nano V.3 digital pocket oscilloscope is it good for measuring electronics appliances like TV,Computer,SMPS, LCD Monitor etc.?
The bandwidth is too small (1 mhz) thus it is not suitable for checking electronics appliances.
what is the difference digital capacitance meter and esr meter? it can do the same function?
ESR meter is much more accurate in checking e-caps while the digital capacitance meter just measure the capacitance. Many times a failed e-cap could have good capacitance but bad ESR Value.
there is 1 shop sell 2nd hand digital capacitance meter for about 80 ringgit, it is worth it to buy?
Digital capacitance meter can be used to check on non polar cap but not recommended to check on e-cap.
Thanks for your reply I have repair tv dead set Brand name Alfaris and i found defective horizontal transistor 1803dfx,
and leak filter
capacitor 100uf/400v if posible i can replace capacitor value is 180uf/400v.
Yes you can.
If you don’t mind i have also question problem tv samsung model#cs21A530fl.
the screen is small like a low voltage i change power supply filter capacitor but same problem
Also the pcb chip ic. the voltage outpot secondary chopper transformer is ok 120 volts.
may be the flyback hi-voltage diode leak.
It could be the horizontal yoke coil shorted or the pincushion transistor/h.size circuitry have problem.
Yes the output of the regulator IC is going to the lcd panel, but I don’t know what is the output voltage since it is only written RDM 117-A ( as the attached photo ). How do we know what is the output voltage should be? Many times I see regulator ICs which don’t write the exact output voltage on other equipment.
I face this kind of problem too. But for LCD Monitor it is usually either 1.8, 2.5 or 3.3 volt.
2 SMD transistors are associated with the input of the regulator IC, one is S72, the other is A32B 2F ( 2F is written with smaller character and perpendicular to the A32B, what is the meaning of this additional smaller coding ?).
Although i could not get the exact answer, to me it is just like a version.
There is another S72 SMD transistor somewhere else with different flick result with analogue meter, is this a good clue that one of the SMD transistor is bad?.
Remove it and short the 3 pins and if you still get different reading then chances is high one of it have problem
Checking these two transistor onboard don’t seem to be a BJT or FET. The SMD Codebook doesn’t have these data. Where could we find the datasheet of them, the revised edition of the Codebook?
Click on the pdf and see the Mechanical data in the pdf file and the marking is S72
Another question is about a SMD resistor written looks like D1C. Have you ever seen this kind of SMD resistor marking?
I have tried to search fro it but sorry no data. No i have not seen such part number before.
Just want to know if i check the primary winding for the power transformer using multimeter, meter shown short circuit that means transformer primary winding good ? if meter shown high resistance means primary winding open circuit???
Primary winding only can be checked by using Ring Tester. Meter is not accurate. It can only check for open circuit.
Hi jestine, how are you doing, thanks alot for the answer, I have another question jestine, please answer me when ever you have a chance cause I know you are very busy, I’m working on a Sanyo LCD TV, I think is 42", symptom: TV doesn’t turn on at all, so, I started cheking voltage on the power supply board just like on a monitor, the brige rectifier gave me 120 AC volts
, then I checked the voltage on the big filter capacitor and I was expecting about 150 or 170 DC volts on the capacitor and it gave me cero point someting ( 0.0292 volts something like that ),my question would be, is the problem between the brige rectifier and the big filter capacitor? I dont have the schematic but I think there are some ceramic capacitors, inductor, diode and the primary side transformer, I already tested an inductor, a diode, the big filter capacitor, they are good, but I still have test the others components. Thanks jestine. Hopefully you give me some tips or advice here.
You need to trace from the output of the bridge to the filter cap. There could be an open path.
Dear Jestine Yong,
On switching ON my PC Monitor, the screen colour went to pink and as I had some
important work which needed to be completed on time, I had to carry on working
with this faulty colour but after working on my files for about five minutes the
screen reverted to its original nice brighter colour. Do you have any idea what
has caused this?
Good day and keep the good work.
It could be a dry joints in the crt board or the vga cable connection intermittently broken. Try open up the monitor and gently tap on the crt board with the handle of your screw driver.
Hope you are fine and good first i want to tell you i have made dick smith flyback tester after soldering the components and connected 6volts to it.
It should be connected with 9 volt battery.
It show one red led on and when i touch it hot output lead with my finger it shows full 8 led on please tell me it is working perfect or something wrong thanks
Yes when you trun on one red led should light up and when you short the probe the led will off. If you check on bigger winding like flyback primary winding it should light up all LEDs.
About your suggestion of: Remove it and short the 3 pins and if you still get different reading then chances is high one of it have problem
Assuming the transistor is a FET we need to test it offboard which is much accurate than checking it on board. The reason i have asked you to short circuit the 3 pins with wire or any metal is to discharge the internal capacitor so when you want to compare that time at least it will give the same reading. In other words, if one fet you did not discharge and the other one you have discharge both will give different result when you compare it.
Hello Mr.Jestine…saya nak minta tips dari Encik Jestine.
Saya sedang troubleshoot sebuah LCD jenama Acer.Masalahnya sekarang screen dia bila switch on power keluar putih aja.Saya dah check capasitor tapi semua dalam keadaan baik.Pada pandangan Encik Jestine bahagian manakah yang menyebabkab screen LCD ni menjadi putih (white screen) ?
Saya harap Encik Jestine dapat membantu.
Sekian,terima kasih saya ucapkan.
Tiada supply voltage ke LCD panel boleh menyebabkan white screen. Dan juga LCD panel board rosak pun bolh menyebabkan white screen. Sila check samada voltan ke LCD controller board.
Sir, i have a problem with sharp tv model 14R2MK2 The problem is that when i turn it on you hear only a tick-tick sound coming out, i cheak the s.m.p.s i found it okey then i disconnet the B+ to the plyback transformer then the standby light come out and no more that tick-tick sound. Sir should i suspect the plyback transformer or their is another componet to suspect?. Thanks
I just started maintenance on older printers with a relatively small, simple smps. These output 36 v dc. I am finding that the broken ones are powering up to full 36v then gradually decrease to 0v then cycle up to the full 36 v dc. This happens repeatedly and I am having trouble finding the component or components to look at. There are several tiny diodes on the pcb. Can you guide me as to what to look at. Thanks
Did you connect the power supply to the board as in certain power supply, it will become cycling if there is no load. Assuming this power supply ca work without load and still cycling then you may need to check all the components in the power side. It can be bad ecap (bad esr), resistor turn into hiher ohm especially the current sense resistor and even semiconductor like diode or transistor that can breakdown when under load. Check those filter caps too at the secondary side for bad ESR.
After I got the S72 pdf file from you, I just knew that the D pin is in the centre. Before I assume the D pin is on the left ( I refer to S71 pins ). So now checking again with analogue meter confirmed it is OK.
This mainboard is using FP5451 dual channel PWM control IC and seemingly this mainboard is using it as dual output switch regulator with 2 pcs of 9435 ( P channel Power-Trench MOSFET ). One 9435 outputs 5V, but the other one output voltage is 0 V. I had tried to replace this 9435, but got the same result. Then I took out the Inductor to see if there is any output voltage from D pin; but unfortunately powering the monitor on without this inductor might have done some harm to the PWM IC or the Power-Trench driving transistor causing this monitor led indicator lit for less than a second now ( both Power -trench output is 0V now ). I don’t know how to hand over this unit to the customer now.
Yes in certain circuit without the complete component (removal of the inductor in your case) it will cause other components to fail.
Could it be one channel of the PWM IC was bad before I took the inductor out, causing no output voltage at inductor?
Yes there is a possibility.
But checking with scope there were waveforms at both OUT1&2.
I suggest that you do a ohm (set to x 1 ) test to compare both the circuit. I hope that you could see the different in the resistance since you said the IC produced good waveform.
Check the vertical ic. make sure no dry joints and the supply voltage is good. If all checked to be good then direct replace and retest.
Hi Justine! I have got problem with customer SUBWOOFER,the STK IC SLA 6023 burnt,but it has two IC the same one of them failed which is that SLA 6023,I try to find another in order to replace bt i didnt get the same IC, so can i use another STK IC which can be the oppose of that one,
You need to replace with the same type of ic. Usually before replacing the ic and turn the set on you need to check the surrounding area first. Have you tryhttp://www.utsource.net ?