Monday, September 8, 2014

Blog follower from Philippines want to know a few things about CRT television repair


Good morning, I read your article recently: the Understanding of CRT television critical voltage test points...

I was confused a little bit about the word B+ ...I want to clarify this because as a newbie in the field of electronics, safety first is my goal when rendering my services to others...

My question is this: all transformers “s.m.p.s transformer, drive transformer, and the fly-back” are producing a B+, right?

Transformers do not produce any voltage Alex, they just transform (change)

For example they can step down or step up the voltage/current.

But remember you cannot have the two (current and voltage) being increased or decreased at the same time.

Take for example the transformer used in your radio rated 240VAC to 12VAC.

The 240VAC is stepped down to 12VAC, in this case we will have the voltage decreased but the current will increase and that is why you see the output wires of most step down transformers are thicker than the primary side because of this high current.

For drive transformer this is also step down transformer but in case of drive transformer they are basically used to match impedance.

Here are the list of primary power supply is composed of : 1 Fuse, 1 surge limiter,1 main capacitor,bridge retifier < 4 diode> 1 smps transformer, 2resistors in series ,1 posistor1 ,3 ceramic capacitor, 1 degaussing pin, 1 power pin, many jumper line, 4 signal diode...Secondary output supply is composed of 4
diodes that is carrying a dc voltages taken from smps transformer, filter capacitor ranging to 160v, 100v, 50v,25v,16v and 10v,, right?

Sure Alex, this is a good description of common power supply components found in switch mode power supply (S.M.P.S)

But I have a comment on your remark on the secondary diodes…since the output of any transformer is AC current, that is why we have the secondary output diodes which are used to change(rectify) this AC back to DC current.

The diode only manage to rectify the AC signal into Pulsating Direct Current, this is still not clean enough to be used by the circuits and that is why capacitors comes in handy to smooth this pulsating DC into clean DC ready for use by other circuits.

About horizontal driver series is composed of: 1 driver transformer, 1 driver transistor, driver resistor and the final destination is the HOT Transistor ...Now master my question is where can I find the B+ among the electronics components mentioned above?

The best place get this B+ is at the positive leg of the Capacitor you mentioned earlier rated 160V, whenever you see a capacitor on the circuit and want to guess the voltage on that line it is filtering just consider the working voltage of the capacitor used to filter that line…if it is rated 160V just divide that by 2 and you get 80V…so expect the voltage on the line to be between 80-100, this is just a rough estimate of what to expect thought.

Another good point of getting this B+ is the middle leg (collector) of the HOT transistor.

About R-red, G-green, B-blue cathode pins, at sight , how can we know the RGB cathode pins points? In this regards we need to be accurate pointing pins because the printed layout of all PC board is not the same.

Usually these are labeled like KG, KR, KB and should not be a big issue here Alex.

I am planning to buy a book CRT television repair course thus I am worried1… the pictures you Have shown is not the same with the unit I am for example the picture of pins Fly-back transformer, page 6 of understanding the CRT television critical voltage test points, the B+ is away from the fly-back transformer, it should be the pin of fly-back transformer has a B+. How come the two points has a B+...I am confused...Please show to me the B+ points.

In electronics Alex, what is important is to get the basic concept and then you can apply the same to any other TV model which shows up at your workbench.

Having said that let me say that I have written my book from the technician work bench point of view and you can confirm that from testimonies of satisfied customers who bought this book.

Anyway,,,I am worried to buy a book because it did not show the complete details or picture of B+.

Oh! Alex, this means you status in electronics repair will remain stagnant and this is not a very good report unless you want to change your career to something else.

All the best my friend.

Thank you Master.

Alex Ancheta L.I.B


1 comment:

  1. Mr Alex your qustion is about +B and you have directed and informed by Mr Kimathi that capacitor marked 160V + pin and collector of Hot is the place where you can get +B.Some manufacturer mark flyback pins but others do not.i have buy this book and help me more,My advice to you if you want to stay in this field please buy this book and many others.