Samsung syncmaster 450b replaced defective transistor d2125.2e with BU 508 DF then every thing ok for 120 second maximum and then I hear sound like
Like that sound (zezeze…) and then screen vibrate and monitor power off itself

I told you on the other site you can not use BU508 they are crap for monitors use BU2525 if an external damper diode is fitted if it is not fitted then find a "fast" transistor with one at at least 12A collector current.

Rich

Thank you rich for your help
I used BU2525AF (SI-N CTV-HA 1500/800V 12A 45W)but
The same problem and the time of power on decreased
afriend tell me to use BU2525dF!!
please tell me which type can work properly

Hi did you check if the unit has a diode on the PCB connected from the collector track of the HOT to the emiiter track, there may be 2 in series, If not you need a Transistor with an internal damper diode. The other thing to check is the B+ regulator device this maybe a Fet or a bipolar device which often fails when the HOT dies thus when a new HOT is fitted it is also killed as the B+ regulator can not work. I will help you more on Moday as I am at my parents and have no schematics here.

Rich

thank you again but I did not find diode connected from the collector track
So which type of transistor I can use?
I am new in this field so I do not know where the B+ regulator
Is it voltage regulator connected with on / off power switch and how I can check it?
I have also big problem I can not find the schematics for this monitor

Hi can you tell me what the transistor pcb ref is please ie Q???.

Rich

voltage regulator ic 601
the transistor is Q402

did you test your highvoltage transformer?
that might be what you heard.

Hi i have searched high and low but cannot find a schematic for the 450b. Does the transistors Q402 ollector connect to the EHT transformer ? if so it is usually pin 1 and pin 2 is the DC feed, on pin 2 there may be a capacitor check this cap, now how does the DC get to pin 2 is it via a diode from a fet connected to ground or from a fet connected to a high voltage rail trough a coil then to pin 2. If it is from a high voltage rail then check fet. If it is via a diode then remove this diode replace the transistor and use a variable PSU to inject DC into pin 2 use a scope to look at the collector of Q402 wind up psu and observe waveform. I have uploaded a Document to,

http://tibor56.hyperlinx.cz/index.php

called power devices in TV's and monitors.

This explains deflection circuits very well.

Rich

HYa,

You can download the schemas at this
URL:http://www.eserviceinfo.com/download.php?fileid=5715 by two ZIP files. I heard that model 550v is similar to 450b, 450Nb and 550s models. Anyway, ih this website you can find other schematics too.

Cheers,

-Eduardo.

Did you check to post dates Eduardo this was an ancient request.

Rich