CRT monitor

[felto]

My computer monitor just went on the frizzs.
So I decided to open it up and investigate.
I do not see the obvious burnt component
and also checked out the fuse if it was burnt.
I put a voltmeter on the output transistor
and I get around .6 volts which tells me that it
is probably good.  Can anyone give me some advise
on what can be wrong with my monitor.  I get no power
coming out of the unit when I fire it up.  I would really like to
fix this because it is a sony monitor and payed alot for it.
Any advise will be greatly appreciated. Thanks

 

[windoze killa]

You haven't supplied enough info. What do you mean you don't get any power out of it? Do any of the LEDs light up? When it is on place the back of your hand against the screen and see if the hair on the back of your hand stands up, if it does then you have EHT. Can you smell any brown smells? Did it go bang? Any horizontal or vertical lines? Little dot in the centre of the screen? How did you measure .6V on the O/P transistor (if it is one)? Were you measuring the base, emitter or collector?

If you can answer some of these we maybe able to help more.

 

[SM2GXN]

Just an add to windoze killa excellent post, what brand and model number?

 

[felto]

It is a Sony monitor and I dont remeber the model no.
I do hear it making a sound when it is turns on.
The LED power light does not come on when I
power it up.  The screen remains blank when I
power it on.  As for the output transistor I do get
a .6 volts across collector and emitter when tested.
But I get an open between the Base and the Emitter.
What is EHT?
Let me know if you need more info
Thanks again

 

[SM2GXN]

EHT= high tension.
Some of these horizontal output transistors (HOT) have damper diode built in between collector and emitter that might be the reason why you get .6V, try to swap testleads and if you get same .6 volts the transistor is probably shorted, measure resistance across collector/emitter instead of  diode.
If the HOT is shorted chance is that the step down converter could be faulty as well, if the coil is shorted you might have to wind one by yourself these are usually not an easy to find spare part  ???

 

[windoze killa]

Just to be picky, EHT = Extra High Tension. generally around 26KV for a monitor. A very good reason to be carful when poking around inside. It really hurts. And can leave a little burnt pin hole in your finger. OUCH

 

[felto]

Step down converter you say.
Is that the same as the flyback transformer?
Is there an easy way to check this part
without disconnecting it from the board.

As for the HOT what readings should I get
out of it.  by doing the diode test I think getting
the .6 volts is sufficient no? 

What else can I check on the mainboard that would
likely be the culprit?  Thanks always for your help

 

[felto]

I forgot to ask  you on my last post.
What value should I get when checking
resistance on collector-emitter junction
of the HOT?  Do I set the volt and the
highest resistance scale?  Let me know

 

[SM2GXN]

I don't even know if your monitor has step down converter, a schematic would be a great help, the step down converter supply collector voltage for the HOT, if this converter doesn't work the voltage to the HOT is usually to high and will result in destruction.
Use high res scale I think you would get not less than 1Mohm if you get low reading both ways swap transistor.
Check the model number otherwise all advises will just be a guess  ;D

 

[felto]

Whats a good site in trying to find a replacement for
the Horizontial Output Transistor?
thanks

 

[SM2GXN]

Sounds like you figured out that the HOT was the culprit, about you question, it depends on where you live, what kind of  transistor is it?

 

[felto]

New York City
The part no. for the HOT is C5302
hope that helps

 

[felto]

I have another monitor that has one can I just
swap to into this one.  The part no. is different and
I dont know if these things are interchangeable.
Will that work?

 

[SM2GXN]

C5302=2SC5302 these are japs
No you can not just swap to another transistor unless you know it is an true replacement.
Check the transistor you got in your spare monitor and let me knowwhat type it is.

 

[felto]

The Horizontal Output Transistor from my old monitor
is part no.  DE9704

 

[SM2GXN]

Is DE9704 the marking on your transistor? I'm sorry but never heard of it please check again 

 

[felto]

That part no. is from the working monitor
as for the non-working one the part no.
is C5302

I checked the diode test from C-E junction
and it get a reading of about .4 volts
Is there another test from another junction
that I can hookup my meter to?

 

[ante1]

This is the one: http://wwww.ges.cz/sheet/2/2sc5302.pdf

 

[SM2GXN]

Thank's Ante!
The 2SC5302 doesn't have any damper diode built in between collector and emitter.
If you have unsoldered all legs there should be an infinite resistance between collector and emitter if not then your transistor is smoked, be sure that no legs are in contact with the the pcb traces.