"d6xkr via ElectronicsKB.com" u45258@uwe wrote in message
news:885177717897a@uwe...
Robin Taylor wrote:
actually there is that diode just after the smps transformer but i don't
know
exactly if it is operational or not as it didn't grab my attention. i'll
check on it in the morning.

The Diodes after the the SMPSU are secondary rectifiers, they're most
probably ok.

You are looking for a big diode like this:
http://www.nxp.com/acrobat_download/...ts/BY448_2.pdf
near the line output transistor, this is the transistor most likely
screwed to the aluminium box/heatsink surounding the line output
transformer. http://en.wikipedia.org/wiki/Flyback_transformer

I have seen this diode fail, in a few monitors, when it fails it
effects width and east/west correct,(pincusion).
All this said its been at least 10 years since I was fixing monitors.

Good luck,

Robin

i red this paper which gave me an idea about the larger picture of
horizontal
sync. http://www.repairfaq.org/sam/reppic/horiz-tv.pdf, and i think it
said
the same as you suggested, there is a problem with a peripheral component
around the flyback transformer. i also checked on the flyback trans. and
the
components around it, i found the damper diode and it checked right it's
operational, but it looks like a regular diode except for it's a little
bulky
and brownish in color. i found also another diode that looks like the one
the
datasheet you posted mentioned, it has a glass casing and it's oval in
shape
but it's very small and white and it's operational too.

the numbers of both the diodes are;

1. rg4a bulky one 2. 33ipn small one

finding that every thing is fine with these, i tried to check every
component
around the flyback transformer. every thing checked ok, nothing seemed
damaged, there were two more diodes and they were ok, there was a coil and
it
checked ok too. and a n-p-n BJT and it checked ok too. an elecrolytic
capacitor was there too and it was fine, but i'll recheck on it again may
be
replace it, i already got a new spare one.

not only this i checked on all the FETs on the pcb and they all were n-
channel type and they were fine. i have diode checker in my multi-meter
and
it shows the biasing voltage if the diode is operational. all of the solid
state devices i've checked were ok. all the BJTs around were ok too, and
the
diodes that were away from the flyback transformer were ok too. everything
just looks fine, no burnes, no exploding or leaking devices, or damaged
not
even a small resistor, which adds much to my confusion. does this have any
thing to do with damage to the flyback trans. itself?

hope any solution that fixes this situation appears in the horizon.

thanx

--
Message posted via ElectronicsKB.com
http://www.electronicskb.com/Uwe/For...epair/200808/1

To be honest, I think that you have reached the point where you can't go
much further without a set of schematics and a 'scope. You need to see how
E-W raster correction modulation is achieved, and then to see why it's not
happening. It's usually not quite as straightforward on computer monitors,
as it is on a TV set. This is because the TV set runs at a constant line
rate, so only one condition needs to be corrected for, whereas a monitor has
to run at a number of different line and frame rates. As the line rate
changes, so does the tuning of the flyback transformer, and the deflection
yoke. This results in major width and geometry variations. To compensate for
all these conditions, the E-W correction often takes the form of a FET
modulator stage for the line output HT supply. This is driven from the sync
processor and timebase chip (often a big one at the front of the chassis)
which draws its correction data from the EEPROM. When you change the
parameters via the front panel user controls, these are stored back in the
EEPROM by the same chip. Brightness and contrast data are also stored in
here, as well as auto grey scale and beam current data, which is why the new
blank chip that you tried, didn't work.

I don't know what else to suggest that you do. Did you look on
eserviceinfo.com to see if the Viewsonic with almost the same model number
that's listed, was similar ?

This site claims to have the e653 manual for free, but they need you to sign
up for their newsletter

http://www.protech2u.com/download.html

Arfa