Repair tip: Viewsonic VG700b

BRAND: Viewsonic

MODEL: VG700b
SIZE: 17"

PROBLEM: GREEN PWR LED STEADY ON. NO PICTURE. NO CCFL FLASH.
SOLUTION: CHECKED PWR/MAIN BOARD FOR OUTPUT VOLTAGES TO INVERTER BOARD. FOUND 12V AND 3.3V. NOTHING WITH 5V. ASSUMED THE PROBLEM WAS ON THE PWR SUPPLY SIDE OF THINGS, AS THERE WAS NO 5V WITH BLACK LEAD TO CHASSIS GND. TRACED 5V PIN DOWN CIRCUIT AND DID FIND VOLTAGE (AGAIN WITH BLK LEAD TO CHS GND). DISCOVERED THAT 5V WAS PRESENT AT OUTPUT PIN WHEN BLK DMM LEAD WAS PLACED ON PIN AND RED PROBED TO SOURCE. BASICALLY THERE WAS 5V GOING ALL THE WAY UP TO THE OUTPUT PIN, WHY IT DIDN'T REGISTER WITH REFERENCE TO CHASSIS GND, UNKNOWN. SO WITH THIS INFORMATION, THE INVERTER WAS NOW SUSPECT. I FOUND THE 12V FUSE BLOWN ON IT. MUST SOMEHOW TIE INTO 5V CIRCUIT AND ALLOW IT TO COMPLETE. FUSE WAS RATED AT 4 AMPS, REPLACED WITH 5 AMP. WORKS GREAT!!!


UPDATE: USING A HIGHER RATED FUSE CAUSED A FIRE TO START INSIDE THIS MONITOR. WHICH QUICKLY SPREAD THROUGHOUT MY HOME AND DESTROYED EVERYTHING I HAVE EVER OWNED. I THINK NEXT TIME I'LL USE THE 4 AMP FUSE.
 
PS. Don't tell my insurance company about this little slip-up. Thx!

Dell E172FPb REPAIR TIP

BRAND: DELL

 

MODEL: E172FPb

 

SIZE: 17"

 

PROBLEM: GREEN PWR LED
FLASHES. ABOUT ONE SECOND INTERVALS. NO PICTURE SEEN AT ALL.

 

SOLUTION: ONE (OR BOTH)
2SC5707 TRANSISTORS WERE FOUND SHORT. THERE ARE 4 TOTAL ON THE BOARD. 2 PER CCFL
DRIVER. THESE WORK IN CONJUNCTION WITH ONE ANOTHER, SO WHEN ONE GOES OUT, MIGHT
AS WELL CHANGE THEM BOTH OUT, AS DAMAGE MAY HAVE BEEN DONE TO THE OTHER AS WELL.
WHEN THESE GUYS FAIL, IT USUALLY TAKES OUT THE PF751 FUSE (3A BELL) WITH IT. IN
THIS CASE IT DID NOT. SCREEN WORKS GREAT NOW!

 

gateway fpd1730

 

The gateway fpd1730 monitor is so easy to fix I was surprised. What fails is a mini brown colored fuse on the small board that is next to the main board. I remove that 4 amp fuse and solder jumper leads to the connections and then install a 5 amp fuse. If this doesn't fix the problem and the screen flashes for a second there are two transformers on that same small board. What happened is the solder gets hot on these connections and when they cool off the solder doesn't give a good connection. All I do is resolder all of the leads on those transformers. I have fixed 4 of these monitors and all 4 repairs have been reliable. That inverter board is listed for sale online for 75.00 and I would say my repairs take maybe 15 minutes and you can get your monitor up and running a lot cheaper. I did buy some magnifier glasses that help me but those were only 2.00 surplus compared to 12.00 at Walmart and 18.00 at Barnes and Noble. Gateway screwed a bunch of people with this model LCD screen but since it is so easy to fix my hat is off to Gateway

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More Tips…

Troubleshooting DELL E173FPB LCD Monitor with power blink symptom is quite easy if you know the right procedure to test it. There are two sections in the monitor that can cause power to blink. It is either primary or secondary section or even sometimes both sections can be faulty. So to isolate as which section is giving problem. I used an automobile 12 volt light bulb (brake light) and connect it between the 12 volt supply line and cold ground with the fuse removed.

 

If the bulb still blink chances is very high the power primary section have problem.

 

Do not overlook the other voltages line as well such as the 3.3 and 5 volts. If any components shorted that gets the supply from the 5 and 3.3 volts, the power also may blink.

 

If the 12 volts bulb lights up we can assume that the power supply is working fine and something shorted further down the line that makes the power supply to blink. If the bulb lights and you continue to check the power section, it will be going to waste your time. You should now concentrate on the secondary section circuit such as the four transistors C5707 that drive the high voltage transformer in the inverter board.

 

Just think these transistors like horizontal output transistor (HOT) in the CRT monitor that drive the flyback transformer where it worked so hard and chances for it to breakdown is very high. Checking the four transistors off board found one of them have a shorted reading with an ohmmeter.. This transistor can get faulty by itself or it could be some others components that caused it to develop a short circuit such as a defective high voltage transformer but all of the four high voltage transformers checked to be okay with ringer and ohmmeter test.

 

Now, here is the secret that I’m going to reveal. If you just replace the defective transistor only, chances is very high the transistor or another C5707 transistor will breakdown again. Usually what a technician does is to test the other transistors with either an analog or digital meter. If you use both meters to test the transistors then you have missed out on the faulty transistor because both meters won’t reveal to you the hfe reading of the transistors. Only some digital meters have the hfe checking feature. In other words, you have to use test the hfe reading of a transistor. Although you can replace the other three transistors directly, why not we do some detective work to find the cause of the problem?

 

 

Using the Peak electronic atlas component analyzer, I could clearly see the different between a good and a bad transistor. A good C5707 transistor has hfe reading from 320 to about 390 but the bad one reads 467! The other two C5707 transistors have reading about 350. In the above case only two C5707 transistors were replaced and you save the other two. I had burn in test this LCD monitor for many days and it worked perfectly fine.

Conclusion- Whether you repair the DELL E173FPB LCD Monitor or any other model such as the E172FPB or E171FPB, basically the testing method is the same. You could also use this testing procedure on other brand of LCD Monitor too.

 

 

 

Repairing the DELL E153Fpc LCD Monitor with the complaint of display shutdown after few seconds (power LED still on) was not difficult. Normally when this type of problem happens, we would

 

first suspect the inverter board,

then the filter capacitors and

lastly the main board.

 

A defective in one of the lamps and a faulty TL1451AC PWM IC or inverter ic may caused the display to shutdown as well.

 

 If the lamp is defective, it will send a feedback to pin 3 or 14 of TL1451AC IC and caused it to stop producing output signal thus the display just shut off once you switch it on. The power board is using a SG6841D pwm ic and a FQPF7N80 power fet . If this power section blow, it is quite easy to troubleshoot because it has fewer components. You can also use other part numbers to substitute the power fet.

 

 

As usual, after opening up the cover, I would first check for any burnt components, loose connector, cracked board, dry joints and etc before doing the voltage test. As for the lamps, I would check it last because lamps were seldom spoilt. Upon scanning for any bad components before starting the voltage test, I found a filter capacitor that had turned into darker color. Using the ESR meter revealed the ESR ohm has shoot up to 12 ohms. This filter capacitor located at C922 with the value of 1000 micro farad 16 volt. If you don’t have the ESR meter you can always use the digital capacitance meter. The value that I got from measuring the bad capacitor was 57 microfarad. If you don’t have ESR meter, make sure you get one-it’s fast and accurate.

 

Now, the question is why a filter capacitor can cause the display to shutdown? If you carefully see the picture, I’ve drawn the yellow path to show you how the voltage is flowing. By the way, the voltage at the bad filter capacitor line is 12 volt. The voltage passed through a SMD transistor in the start circuit and flow straight to pin 9 (VCC) of TL1451AC IC. In order to let the 12 volt to flow through the transistor and reach the vcc pin of the ic, first, a ‘on’ signal must be sent from the main board to trigger the transistor. If no signal send to the transistors (off signal), both transistors can’t be turned on and no voltage will follow through the ic. Thus if the main board or any of the start circuit components spoilt, there will be power but no display because the TL1451AC would not send signal to the Royer type L, C resonant and boost circuit, so no high voltage produced by the high voltage transformer and this will lead to no display.

 

In the above case, the LCD Monitor display shutdown was due to the ripple because of the bad filter capacitor. The ripple caused the TL1451AC IC to be unstable and eventually shutdown the output signal. Replacing only the filter capacitor solved the DELL E153Fpc LCD Monitor shutdown problem.

 

 

Conclusion, don’t always presumed that LCD Monitor is very tough or difficult to repair. From the above article, you could see that the caused of the shutdown problem was only a bad capacitor. If you fully understood how LCD Monitor works, then chances for you to successfully repair the monitor is very high but again it depends on the availability of spare parts. If you ever come across any LCD Monitor sent to you for repair for the first time, go ahead and start troubleshoot it. Who knows one day LCD Monitor repair could become one of the major source of income to you and your business.

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DELL 172FP AND BENQ

BRAND: DELL

MODEL: 172FP

 

BRAND: BENQ

MODEL: 17" MODELS

 

PROBLEM: DELL  172FPx  and BenQ boards are the same. Commonly plagued with CCFL driver issues.

 

SOLUTION: This can be isolated to 99% of the time to the transistor pairs of 2SC5707 located at Q751 etc. Also, PFU9024 transistor is suspect. Any or all of these will likely take out PF751 3Amp Bell Fuse.

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MPC F1750i 17″ LCD Display

BRAND: MPC

 

MODEL: F1750i

 

SIZE: 17"

 

PROBLEM: BACKLIGHT SHUTS OFF AFTER 2-3 SECONDS.

 

SOLUTION: C922 1000/16 CAPACITOR FAILURE. ALSO LOOK FOR BOTTOM BLOW OUTS ON SMALL PURPLE CAPACITORS. REFLOW ALL MAJOR JOINTS AS MANY WILL BE CLOSE TO FAILURE POINT.

 

REPAIRED: DELL E151FPp

 

BRAND: DELL

MODEL: E151FPp

SIZE: 15"

SYMPTOMS: SLIGHT BACKLIGHT FLICKER

CAUSE: 100/25 CAP BAD ON INVERTER BOARD. 

 

REPAIRED: DELL E151FPp

BRAND: DELL

MODEL: E151FPp

SIZE: 15"

SYMPTOMS: NO POWER

CAUSE: 220/25 CAP BLOWN; GREEN PICO FUSE NEAR CAP WAS OPEN.

 

By Jestine Yong…

Tuesday, March 18, 2008, 8:06:35 AM

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Monday, June 13, 2005, 9:11:23 AM

The fast and proven way to accurately test a diode using analog multimeter.

Testing Flyback Transformer - How to Test and When to Replace It

Tuesday, June 07, 2005, 8:08:41 AM

Fast and easy way to understand and testing flyback transformer. Nowadays, more and more monitor comes in with flyback transformers problems. Testing flyback transformers are not difficult if you carefully follow the instruction.

How to Read Zener Diode Code

Thursday, June 02, 2005, 4:01:48 AM

Learn the simple and easy way to read zener diode code number. Many technicians are confused on how to really read a zener diode code. There are many types of code number indicated on its body.

What is EEPROM ?

Monday, May 23, 2005, 11:31:51 AM

Understand the functions of EEPROM and how it fails... EEPROM is also called a non-volatile memory because when power is turned off the stored data in the EEPROM will not be erased or intact.

Electronic Books And Magazines Can Be Among Your Cost Effective Servicing Tools

Monday, May 23, 2005, 11:31:06 AM

The easiest ways to upgrade your electronic repair knowledge is by reading electronic books and magazine. A few dollars spent on the right book or magazine can earn you hundreds of dollars. It opens up a whole new world of never ending knowledge. Always be on the lookout for good books and magazines.

How to Solve Multiple Paper Loading Problem in HP5L and HP6L Laser Printer

Monday, May 23, 2005, 11:30:14 AM

Learn the simple ways to troubleshoot your own laser printer without sending to a laser printer repair center.

How to Read CRT Tube Part Numbers

Monday, May 23, 2005, 11:29:32 AM

Easily and quickly understand the code number of picture tubes or crt...All picture tubes, whether monochrome or color type are identified by a specific code consisting of numbers and letters. The codes are different from each other because different tubes have different characteristics.

What Is A Crystal? And How To Test It

Monday, May 23, 2005, 11:28:53 AM

Simple ways to understand about the functions of crystal and how to check it...

Setting Up as an Electronic Repair Authorized Service Center

Monday, May 23, 2005, 11:23:13 AM

Understand the procedure on how to set up a electronic repair authorized service center...Setting up from scratch as an Authorized Service Center is not an easy job. Your workshop needs to meet the manufacturers' requirement first

Understanding Transistor Data and Replacement

Monday, May 23, 2005, 11:21:52 AM

If, for some reason, you can't get an exact replacement for the transistor that you want to replace, you can refer to one of the transistor substitution guides or book, and try to identify a "near replacement". Beware, however...

What Is A Fuse? And How To Test It

Monday, May 23, 2005, 11:21:27 AM

A fuse is a very thin wire, which either melts or vaporizes when too much current flows through it. The thin wire may be made of aluminum, tin-coated copper or nickel. The resulting open in the circuit stops current flow.

What is ESR Meter?

Monday, May 23, 2005, 11:20:40 AM

All capacitors have a certain amount of resistance to the passage of AC current. ESR (Equivalent Series Resistance) is the sum of all internal resistances of a capacitor measured in Ohms...

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HP F1723 LCD Monitor Repair - No Power

 

This HP1723 17" LCD Monitor came in with the complaint of no power. Upon further inspection I could hear a soft intermittent sound coming from the both front speakers. Since the speakers can produce some sound, this indicates that the power supply should be working fine and it may be some bad components located at the secondary side that had caused the power supply voltage to drop not to start. The power LED doesn't light because the signal was coming from the Microcontroller (MCU) IC. This means that if the MCU did not receive the right voltage from the power supply, it will not send output voltage to the power LED.

As usual, to open LCD Monitor cover , one have to be careful of not scratching or leaving a mark on the plastic casing otherwise the customer may not want to accept his or her broken or badly scratch LCD Monitor. Once the cover have been removed, you have to remove another four screws (two at each side) in order to take out the power/inverter and the Main board. For some LCD Monitors, the moment you have open the cover, you could easily remove all the boards.

The power supply and the inverter circuit are in one board while the Main board and the audio board are in separate board. As mentioned before in my previous articles, I do not immediately begin to troubleshoot and repair any board unless I have scanned all the components with my eyes first. The power supply/inverter board look very new and the most obvious sign that I could see was two filter capacitors (1000uf 16 Volt) had a slight bulge on top of its casing. I believe these bulged electrolytic capacitors that had caused the power supply not to function properly. I have checked all other e-caps too but all found to be good.

Usually whenever a filter capacitor located at the secondary side of switch mode power supply (SMPS) have a too high ESR value, the voltage will drop more than half causing many circuits won't work. Since I already found the bad e-caps, I have to be certain that the secondary diodes (this LCD Monitor is using Schottky diodes) don't go faulty or leaky too. Upon checking the Schottky diodes (part number are SRF20100C and SP10150) I found both of them to be working fine. Replacing only the two bad e-caps with a good one solved the LCD Monitor problem.

Now get this, if you want to be good in any electronic equipment repair, if possible analyze other circuits too. That means if you every time replace only the fuse and the bridge rectifier you won't learn anything beyond that problem and you will get bored easily. Let's take my case for example, after the replacement of the capacitors I will usually analyze other circuits too like finding out what kind of part numbers certain components are using, which type of the inverter circuit is belong to i.e. Buck Royer or direct drive?, why each backlight circuit are using four ballast capacitors?, How many backlights the LCD Monitor is using, what is the inverter IC part number, what is the supply voltage to the inverter IC? How many LED bar lighted up when test on the secondary winding of the high voltage transformer? What would happen if I pull out one of the backlight (will it still work or shut down?). What is the brightness line voltage if set to minimum and maximum? You have to answer all of these questions if you want to be good at LCD Monitor repair. You can apply this kind of questions on other electronic equipment too. This is a continuous process of learning how to be good in electronic repair.

I don't want you to replace caps or fuse everyday without knowing how other circuits function or what are the components used in other circuits. Although to analyze other circuits take you lots of time but I can guarantee you that the time you have spent are worth it. You won't be able to go far if you have set your thinking by just changing components and not knowing the surrounding. If you want to improve in electronic repair then you need a change of mindset in you and only you yourself can make the different! Try this approach and I believe troubleshooting electronic or LCD Monitor repair will never be the same again. Have a great and a fantastic year!