Philips TV 21PT128A/71R: Irregular picture size & shape problem

A TV repair problem that I had recently encountered is with a Philips 21PT128A/71R which exhibited irregular picture size and shape.

TV troubles like this usually indicates a problem with filter capacitors so I visually checked electrolytic capacitors on the main PCB.
One electrolytic capacitor on board location C2453 looked suspicious with its slightly bulging top. Checking the part using a capacitance meter, it read 3 microfarad instead of its indicated value of 680uF/35V.
 I replaced the capacitor with an available part on hand with a value of 1000uF/50V which restored normal size and shape to the picture.
The capacitor is a filter for the +25V scan-derived supply from the flyback transformer.

Samsung TV CS-29Z58MQ: three colored lines on top of picture

I have recently encountered in my repair work a Samsung Slim Fit CRT TV model# CS-29Z58MQ with a problem of three horizontal blanking lines appearing at the top edge of the screen. According, to the customer the problem started with just one line but after some time an additional two lines also appeared on the edge of the picture.
I inspected the board and tried to spot some bulging capacitors with signs of electrolyte leakage which usually cause this kind of picture abnormalities but found none.
Upon closer inspection of the solder side of the main board I saw signs of dry solder on resistors R428 (1.5 ohms, 1W) and on R413 (1ohm, 1W). These two resistors are connected in series with the Flyback transformer's 16.5V supply pin to the vertical output IC LA78045. The resistors are located at the rear edge of the main board beside the flyback transformer.
After resoldering the dry solder on the resistors the three colored lines on top of the picture disappeared.

Daewoo TV DTQ-2072 repeated blowing of fuse

Where can the problem be if the main fuse in the TV power supply blows fuse repeatedly?
This was a problem I have encountered with a Daewoo TV model# DTQ-2072. The fuse blows even when the IC regulator  STR-59041 has been replaced. To isolate the cause of the problem, I replaced the fuse again and disconnenected the PTC thermistor on board location RH02.
I plugged the set to AC outlet and powered up the set from standby. The picture and sound came up but the picture has color smears(dynamic misconvergence) on the sides of the screen - a result of disconnecting the thermistor which passes momentary current to the degaussing coil.
An ohmmeter check on the thermistor shows that it has developed a higher resistance. Opening the plastic case of the PTC thermistor revealed that the thermistor discs are burnt.
Replacing the PTC thermistor eliminated the  color stains on the picture and solved the problem of  blowing of fuse.

Sony TV KV-25JXR20 reduced horizontal width problem

The owner of a Sony TV with model number KV-25JXR20 complained of the reduced horizontal width of the picture of his TV. He also observed "blinking" of the picture which must be his description of intermittent blanking of the picture.
During my initial observation of the problem I also noticed that the vertical size of the picture is in overscan - or stretched - resulting to vertical mislinearity and the presence of red, blue and green blanking lines at the top edge of the picture.
I suspected capacitors with changed values in the vertical deflection circuit and the horizontal deflection or pin correction circuits. Since the TV is already in the vicinity of being ten years of age, I also considered the possibility of dry solder joints.
Since there was no obvious bulging capacitors in my initial inspection of the main PCB I proceeded to resolder the deflection circuits and some parts of the chopper transformer, filter capacitors and rectifier diodes in the secondary circuit of the power supply.
After the soldering exercise, I powered-up the TV again to check if the problem was solved. I was not much surprised to see that the problem still persists since there was not really any obvious cracked or dried up solder joints on the TV's circuit board.
Doing another visual inspection on the component side of the PCB, I noticed the slight bulge on the top of a filter capacitor that was sitting beside the chopper transformer. I desoldered the capacitor and found out that it is a 100uF/160V electrolytic capacitor on PCB location number C609. A look under the capacitor revealed signs of electrolyte leakage. With the capacitor leads still hot from contact with the soldering iron I can still see the electrolyte boiling out of one of the capacitor leads.
By replacing this capacitor only, I was able to solved both the problem with reduced horizontal width and vertical mislinearity.

How to fix an Epson Printer C45 stripping gears noise problem

Most problems that occur in an electromechanical equipment is caused by mechanical rather than electrical defects. And most mechanical defects reveals itself by performing a visual inspection of the mechanical parts. Being able to open the equipment and looking at the parts under the cover is almost halfway to solving the problem.

Take the case of a problem with an Epson C45 printer which I have encountered just recently. The ink cartridge carrier will move to the left side slowly then back to the right side again. As the ink cartridge carrier nears its park position a stripping gear noise is heard and the cartridge carrier appears blocked in completing its travel.

From here on there is no other way to go but to open the unit and inspect what the problem is from inside.

To open the printer I removed one screw located between the label and AC plug terminal at the back of the machine.



To remove the top cover there are four locks that need to be unhooked using a small flat screw driver.

Two of the locks can be found at the back on the lower left and right side of the unit. These locks can be unhooked by pushing through the small rectangular holes.

The other two locks are located at the front and can be accessed through the small rectangular holes located at the bottom corners of the base cabinet. I inserted the flat screwdriver blade through the holes and pried the hooks loose.

After the four locks have been unhooked...




















... the top cover can now be removed.

Once inside the machine I noticed the ink cartridge carrier pressing against a white lever which must be the object preventing it to reach park position.


I pushed the ink cartridge carrier a little bit back...



... then pushed the lever towards the cartridge...



and it snapped into place, no need to use force.
















I plugged the printer to AC outlet, pressed the power button, tested the unit and found it to be working just fine.

Troubleshooting Philips CTV 21PT3932: Black OSD problem

Symptom: Black on-screen display(OSD)
Cure: Replace diode BZX79-C3V9 on board location 6601.
Repair Details:
Set used the L9.1A chassis.
Picture and sound is good; the only thing obviously wrong was that the OSD was black.
When the +3.3V supply going to the microprocessor was measured actual voltage reading was at about +5V. This indicated that the +3.3V supply regulator circuit was defective. The +3.3V supply was restored to its specified voltage output when the BZX79-C3V9 was replaced. Normal color was also restored to the OSD.

Don Matsuda's "Electronic Troubleshooting" - revisited

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The other week, I had an opportunity once again to browse through the book by Don Matsuda “Electronic Troubleshooting”. This was a book that I was fortunate to have bought - and read - many years ago when I was just starting out on doing electronic repairs professionally.

In the preface to his book Don Matsuda notes that Troubleshooting has its own rules. He notes further that the rules are derived from everyday practice and must be taught from the point of view of practice.

Matsuda starts out the book by mapping out a “game plan” for troubleshooting. The game plan is divided into 5 phases.

Phase 1: The Outside

Starts the troubleshooting approach from outside of the equipment under complain. Identify the symptoms. Make the preliminary inspection of the equipment by operating it and evaluating its performance. Decide whether the trouble is in the equipment or the environment. Interview the user to get a background of the problem from his standpoint. Let him know of any problem you see or foresee be before you start out work on the equipment.

Phase 2: The Gateways Into The Circuits

This is when the troubleshooter goes deeper into the root of the problem and begins an approach into the “gateways into the circuits” . Two of these gateways are the input and output devices. Troubles in electronic equipments can be caused by a malfunctioning input device and symptoms will show up at the output. Or the output device itself is defective. Symptoms can be clues that our four senses can pick up or can be measured by our test instruments. An analysis of the symptom is a step towards finding out the right cure.

Phase 3: Working Your Way In

This involves getting down to the nitty-gritty of instrumentation work. DC voltages have to be measured and bad voltages pinpointed. Trace a signal and identify the stage in its path where it deteriorated.

Phase 4: Nailing Down The Bad Part

This involves locating the defect to the bad part. After pinpointing the defective section a test of its components should reveal the defective part/s.

Phase 5: Cooking

This is what is sometimes called 'burn-in test'. After the bad parts have been replaced the equipment is operated for about 20 minutes or longer depending on the type of fault.

In the book, Matsuda also presents some general strategies in troubleshooting. These are:

1. Trial and Error; Divide and Conquer. If something does not work, try another solution. Cut up problems into little ones and deal with them one at a time. Follow up on one of your hunches, if it turns out to be wrong, at least you have eliminated it as a possibility. Troubleshooting is not a cut-and-dried process. But keeping the game plan in mind will keep us from getting sidetracked.

2. Questioning and Thinking Things Over . Question all leads you come across. Poll all possibilities.

3. Playing the Percentages. Troubleshooters pay special attention to parts or sections in an equipment that have a high failure rate. Parts and sections under great heat, electrical and mechanical stress have the highest failure rate.

4. The Divide-in-Half Procedure; Divide and Conquer. Mentally divide a circuit in half and test each half. When you identify the bad half divide it again and test. This dividing and testing is repeated until the defective part is located. This is faster than testing the parts one by one.
   In Steve Litt's 10 Step Universal Troubleshooting Process, the Divide and Conquer procedure is also discussed in detail.

5. Doing the Easy Things First. “When the odds seem pretty equal – and sometimes when they're not – it is best to do the easiest thing first.... At least you will quickly eliminate a possibility and feel better about taking on the more difficult and time-consuming alternative.”

The book then continues by giving valuable discussions and tips on doing voltage tests: what bad voltages tell, which part must be causing the problem. Also very informative are the sections and chapters on checking transistor circuits, amplifiers, power supplies, high voltage circuits, oscillators, high frequency circuits, TV, linear and digital ICs.

Also, the section discussing the “Nature and Frequency of Parts Failures” gives valuable tips on what parts fail most often. The book reveals that the part that fails most often are transistors. Capacitors come in second place as the part that has the highest failure rate. Resistors come third. And then coils and transformers.

In the last chapter of the book which deals with troubleshooting intermittent tough dog troubles, Matsuda advices to get hold of a piece of discarded electronic equipment that a pro technician has wisely turned down and get ready for some real troubleshooting. “However, it is a challenge and a real learning experience, even if you fail.”

In troubleshooting as in life, failure teaches as much as success.

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