Trouble shooting a tv- no schematic?

Question

There are many tv technicians who have done it and I would like to know how one can troubleshoot a tv without a schematic please explain in details!!!

Answer 1

DIVIDE AND CONQUER.....find out what it isn't, and it'll lead you to what it is....



Example : No Sound, has picture.

You know the power supply is working, you know the Audio isn't.

You go to the Main audio amp and measure voltages...Do you have your Power to power the Amp? No? Then you check the Audio amp's power circuit.

If you do have power, then you get out your scope and see if you have an audio signal getting to your amp. No SIGNAL?

Then you follow it back to the Audio processor IC and see if that has a working volume control voltage....If it does then you isolate your work around the processor, if it doesn't you look at the volume control voltage......



Divide and Conquer......

Answer 2

I began TV service when very young. My Godfather owned a TV shop in Binghamton NY

After returning home from the ARMY I began OJT in a TV shop .

This was in the early 1970's and TUBES dominated the

repair market . Even back then Picture tubes were changed

quite often as cabinets were solid wood and technology wasn't advancing as fast as today.

By the early 1980's Betamax and VHS VCR;s were growing very popular due to advances in transistors and IC's both design and manufacturing.

It was in this period of my repair experiance I spent alot of time with schematics.

Both an excellant memory and good comprehension of the materials lead me to troubleshoot without a schematic.

This did not happen overnite it actually took 12-14 years.



Basically what I learned was to divide the problem in half.

And continue to divide it in half until the only thing left was the device in question.



An example common to almost all veteran TV techs is this:

Set is DEAD this means NO RASTER and NO SOUND.

If you run your hand over the screen NO STATIC is present

to indicate HV present from ANODE.



The condition of DEAD can start with the A/C line cord

and continue thru the stack (chimney)of the FBT.(Flyback)

So 50% region to start is at the collector the Horiz Output Transistor. Unsolder the collector from the PCB and then

attempt to turn on the TV measure the DC voltage at the foil.

If you have 115-130 volts DC then collector tuning caps

or pin or lin diodes or FBT are BAD. If you have 0-100 v DC

go back to the Power Supply . Voltage near 100 v DC check filter caps . Voltage very low or 0 check rectifiers and regulators and bias resistors.



Now if you have a TV with good red and good blue but NO green the diagnosis would be totally different.

This circuit starts at the RGB outputs of the video jungle

and ends at 3 pins of the CRT

Experiance would sent the tech to the CRT video PCB

to verify BIAS and fitness of three final Video invertor transistors. If they were all nominal the video jungle IC

would be next point checking the output DC bias and

output waveforms with an O-Scope

And if all in the circuit check good a simple jumper wire to ground attached to the Green pin of CRT would answer the

question

Is it the CRT?



The whole point of my answer isn't that there is a trick to troubleshooting without a circuit diagram



The diagram is for those who don't already know the design

Answer 3

One the things a schematic is to tell you what voltages are present at various points through the set, Now if you have a few years experience of fixing TVs on a day to day basis then you get to know what voltage to expect in most of the set, for example--

12volts on tuner marked B+

45volts on tuner lug marked tuning volts.

Power supply B+ depending on make say 125 155 volts .

CRT base board will have 180 volts for video amps , there is a 2 watt resister for each video amp ( 3 ) that the 180 volts is connected to, if you measure the volts on the other end of the resister it should be 30 to 40 volts less. Feel at the resisters ! they would feel warm if they are doing any work !. I could go on but you should see my drift !

I only need the schematic if there is an out of the ordinary fault !!

You could liken this familiarity with the inside of a TV to a cab driver who knows his city like the back of his hand .

Incidentally I have not looked at schematic for a couple of years but I still know my way round , mostly just use a good multimeter. I hope that this has given you some insight into the mysteries of the TV trade .

Cheers Pete

EDIT.

I don`t believe this ! all good answers giving a personal insight into TV serviceing and not a dick head in sight .

I will say for you --thanks you guys for your valuble input.

Cheers Pete

Answer 4

Its called experience. If you have alot of the same units that comes in for repair, you start to remember how thing should look. Also having a degree in electronics will help alot.

Answer 5

You're funny, why don't you try;

hey mechanic how do you repair motors without a manual, give details.

or hey carpenter how do you build a house?

doctor how do you remove a heart?



It's all about knowledge combined with experience.