Tip & How-To about Televison & Video

How to test flyback without taking it out of the board

A) basically it has to be acted upon by a supply voltage of at least 95V

to work.

b) of course, assuming the horizontal deflection oscillator works, same

with the horizontal drive it should generate output voltages on the

secondary terminals

c) the easiest test point to look when it is oscillating is the CRT heater

voltage, the heater lit when flyback is good.

d) having a voltage reading of 75 V or lesser on its primary pins

indicates a bad or partially shorted flyback, assuming your

horizontal output transistor and power supply are good & OK.


These only applies to CRT type TV's.

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monitor no raster power has been ok


Hello,

The screen is blank with no raster at all. There are indications that the channel numbers are changing in the display. This indicates that some of the low voltages are present but these may be derived from the standby supply.
Assuming there is no deflection and no High Voltage, you either have a low voltage power supply problem, bad start up circuit, or bad horizontal output transistor (HOT) or other bad parts in the horizontal deflection.

Check for bad fuses.

(If you have High Voltage as indicated by static electricity on the front of the screen and you hear the high pitched whine of the horizontal deflection when it is turned on, then the following does not apply).

Use an ohmmeter to test the HOT for shorts. If it is bad, look for open fusable resistors or other fuses you did not catch.
Assuming it is good, measure the voltage on the collector-emitter of the HOT (this is safe if there is no deflection). You should see the B+ - probably between 100 and 150 V.
If there is no voltage, you have a low voltage power supply problem and/or you have not found all the bad/open parts.
If there is voltage and no deflection (no high pitched whine and no HIGH VOLTAGE), you probably have a start up problem - all TVs need some kind of circuit to kick start the horizontal deflection until the auxiliary power outputs of the flyback are available. Some Zeniths use a simple multivibrator for this - a couple of transistors. Others power the horizontal osc. IC from a special line-derived voltage. The multivibrator type are sometimes designed to fail if someone keeps turning the set on and off (like kids playing) since the power rating is inadequate.
Test the transistors if it is that type with an ohmmeter. If one is shorted, you have a problem. The usual way a TV service person would test for start up problems is to inject a signal to the base of the HOT of about 15.75 kHz. If the TV then starts and runs once this signal is removed, the diagnosis is confirmed. This is risky - you can blow things up if not careful (including yourself).

If you hear the high pitched whine of the deflection and/or feel some static on the scree, confirm that the horizontal deflection and high voltage are working by adjusting the SCREEN control (probably on the flyback). If you can get a raster then your problem is probably in the video or chroma circuits, not the deflection or high voltage.

hope this helps......

Aug 06, 2010 | SAMTRON 77V 17" CRT Monitor

3 Answers

WS-65903 HD1080


press format key on mitsubishi remote control and try to get full screen.let meknow if it works if not do you have a cable or satellite box and what type?

Jul 04, 2008 | Mitsubishi WS-65869 65" Rear Projection...

1 Answer

I HAVE A 32 INCH SONY TV AND NOW I HAVE SOUND BUT NO PICTURE WHAT IS THIS


If you still have sound, part of the main power supply is working so the problem is restricted to the deflection-related circuits and probably in the horizontal oscillator circuit responsible for producing the high voltage for the CRT as well as the horizontal deflection. Since it died to a 'dot' the vertical deflection circuit may also be supplied by the action of the horizontal circuit. You will need technical help to restore it.
If you had good picture quality before it died, I would recommend having the set repaired and if and when you decide to buy a new set, store this one (repaired) along with a converter box (for the new digital signal) to use when the new set dies, which it will and much sooner than your Sony. 

Apr 22, 2009 | Sony KV-32S45 32" TV

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