Help with a fault ????

I did a google search on the serial number and go nowhere sorry I can not help more at this moment.

TELL US THE CHASSIS NUMBER THAT SHOULD BE ON THE BACK OF THE SET Have you taken the f$$$$$$ back off the set and seen if the heater still run, or give us more of a clue, come on do a bit more than just tell the useless serial number.

I am hoping someone here may be able to help me with solving an intermittent fault with our family TV....... PLEASE ?. It is a Phillips 21PT2012 / 79R and has what I think is the serial number of BZ000231 723707 on the back cover. The fault manifests itself as sudden loss of all picture, and light from the screen and loss of sound at the same time, anywhere from 5 seconds to a few minutes from switch on. This started a week or so ago, and a turn off seemed to fix it, and now it will not run longer than a minute or so without dying. It seems like the HT supply drops out suddenly, but as I understand it the power supply rails for all the circuitry on this type of appliance may very well all come from one switching supply, and a fault there could wipe out everything? I have a reasonable understanding of electronics, and a good Fluke multimeter, but no cct. diagram, and no experience with TVs. Any suggestions? I think that the set is about 4 years old, and I guess it must be some component that is built to a commercial standard starting to break down, but I was hoping that there may be hope rather than junking it? Thanks for any assistance.

Tim

Hi,

To be honest you are better off getting it to the technician. Philips TVs are generally difficult to fix. Lots of the times problems are quite weird, especially in newer sets.

If you never worked on TV -- IT IS DANGEROUS AND CAN KILL YOU!!!!!! It does not matter how experienced you are with electronics.

Does TV flashes red light when fault occurs? Does Tv reacts to a mechanical shock?

How is B+ when running and when fault occurs? I would check horizontal stage, especially HV caps for the sign of stress. Also I would try to run power supply on dummy load to isolate power supply.

Rudolf P.S. If in Melbourne, I can take a look at it

It may be anything really. One of teh first steps

Always worth inspecting the soldering - most likely lead free solder and inherently unreliable!

First up, be aware that inexperience and TV repair are an extremely hazardous combination. Most TV's have a live chassis, and voltages present can certainly kill.

The failure could be the common DC rail, which will wipe out pic+sound. Or it could be an EHT fault which pulls the common rail down. Or it could be as simple as a dodgy power supply input component.

Clues to check for: any "zap" sound as it collapses; any ticking sound (often faint) once the set has shut down; any smell.

Most sets are fairly generic inside, so an experienced TV tech without a circuit can go a long way, whereas a novice needs a schematic.

Yep, take it to your local TV service tech and keep him in business. You'll spend more time mucking around on your own than what an expert is worth.

TV's are dangerous too, don't play with them.

Dave :)

I dont know much about TV's but what is that ticking sound?

Can't hear it - can you describe it for me? Is it a bomb?

It is the sound of the main SMPS trying to get up, then collapsing under fault/short condition, then trying again.

Ticking sound is pointing to the horizontal fault. I would suspect FBT.

Rudolf

Not necessarily, it can be caused by almost any overload on the SMPS secondary making the PSU repeatedly shut down and attempt restart, a high ESR electrolytic almost anywhere in the supply chain can screw up the regulation with similar results.

FBT is quite common to fail in Philips.

Anyway, without having a TV on the bench one can only guess. I already suggested to run PS on a dummy load and monitor B+.

Rudolf

The OP mentioned flyback lines as the set shut down or attempted to restart, Philips have had a lot of CRT problems in recent years - gently tapping the tube neck with a screwdriver handle might reveal the cause if this is the case.