Mitac LCD monitor - which is HOT transistor ???

[mike]

I have a faulty Mitac LCD flat monitor, model LC552 ( MT15EX6M ) - it
has a problem that I am told is probably du to the horizontal output
transistor - I have the schematic for the monitor, but need help
identifying which transistor on the board is the HOT ???

There are various listed on the parts list, numbers being :

75307D
2SB11245
EZ1084CT
MMBT3904
MMBT3904L

Assuming I am looking for something pretty large looking, the first 3
parts listed are all like this ( the others are all small SMD's ).

Does anyone have any idea which it is likely to be, or where on the
board you would expect it to be placed, i.e. near which other
components ??

I have seen a few mentions of HOT's on other boards and their
placement, but on the LCD monitor it doesnt have an internal power
transformer, tube etc... so I'm at a bit of a loss.

Any help would be much appreciated,

Mike

 

[Steve Bell]

I have a faulty Mitac LCD flat monitor, model LC552 ( MT15EX6M ) - it
has a problem that I am told is probably du to the horizontal output
transistor - I have the schematic for the monitor, but need help
identifying which transistor on the board is the HOT ???

There are various listed on the parts list, numbers being :

75307D
2SB11245
EZ1084CT
MMBT3904
MMBT3904L

Assuming I am looking for something pretty large looking, the first 3
parts listed are all like this ( the others are all small SMD's ).

Does anyone have any idea which it is likely to be, or where on the
board you would expect it to be placed, i.e. near which other
components ??

I have seen a few mentions of HOT's on other boards and their
placement, but on the LCD monitor it doesnt have an internal power
transformer, tube etc... so I'm at a bit of a loss.

Any help would be much appreciated,

Mike

There is no HOT in an LCD display, only in conventional CRT monitors.
Someone is either misleading you or having you on.


Steve Bell

 

[James Sweet]

I have a faulty Mitac LCD flat monitor, model LC552 ( MT15EX6M ) - it
has a problem that I am told is probably du to the horizontal output
transistor - I have the schematic for the monitor, but need help
identifying which transistor on the board is the HOT ???

There are various listed on the parts list, numbers being :

75307D
2SB11245
EZ1084CT
MMBT3904
MMBT3904L

Huh? An LCD monitor doesn't have a HOT, and frankly if you can't identify
the HOT at a glance then you have no chance of succesfully repairing your
monitor.

 

[Jerry Greenberg]

These transistors can all do various types of jobs, depending on the
particular design. Some listed are not generic numbers, and are
manufacture only. Simply going by the numbers it is impossible to know
what they are doing in the particular monitor without having the
service schematics.

As for the HOT (horiz output transitor), I don't want to bust your
balloon, but you were guided wrong about LCD monitors. There is no
scanning as such, so you do not have horiz and vertical scanning.

In the standard LCD monitor, there is a switching power supply, and an
inverter for the back plane lamp drive.

On the back of the panel is logic display processor board, and address
matrix drivers. The A/D may also be built on to this board, or be a
daughter board, or a board on the side.

LCD displays are pixel addressed by a multiplexed drive that is run by
a high speed processor. This technology is very complex, and is not
normaly serviced at the component level. The manufacture normaly
changes the complete board that has failed. When servicing, only some
of the not very difficult parts may be changed at the component
level, if the service cost is not very high to do this. The service
approach is dependend on the phelosphy of the particular manufacture.
They are basicaly all about the same in their service policy.

Most of the failures is in the power supply, and or the lamp inverter.
If the monitor has about 20,000 or more hours of use, it is possible
that the lamps have also failed. In some of these displays the lamps
are an integral part of the display and are not changeable.

Most of the manufactures will not directly sell the parts. They will
tell you to send the monitor in to them for service. They will change
the appropiate module or board to get it working again. If the
manufacture does module or board service level only, their service
department may not even have any detailed schematics. They would only
need the wiring and calibration procedures, and safety testing
information.

Sometimes when adding up the out of warranty service cost and the
shipping cost, it may pay to get a new monitor. The prices of these
monitors have dropped considerably in the last year or so, and are
still dropping.


Jerry Greenberg
http://www.zoom-one.com

 

[David]

Ditto, No doubt the chance of a successful repair is virtually nil.

 

[mike]

Thanks for the info guys, spending time going over the schematic I
managed to work out what most of the trans were doing and had come to
a similar conclusion !

OK then, does anyone have an idea what the problem would be from the
symptoms -

The monitor powers up fine, but as soon as a video signal is
introduced it goes into standy mode ( flashing power light ) ???

Mike

 

[Jerry G.]

Check the refresh rate and resolution that you are driving it with. If it is
out of range for the display, it will go to standby. Start your computer in
the safe mode to check resolution, and refresh rates. The LCD displays run
best in their native mode. Check the user booklet for the proper specs for
your monitor.

If you do not have a monitor that is working to check the computer's display
specs, start the computer in the safe mode with the LCD screen connected.

I am assuming that the monitor is starting up correctly, and can display the
"No Signal" warning when there is no drive from the computer.

Another thought, are you getting the post start-up of the computer displayed
on the LCD screen during the start-up, and windows is not displayed? This
is a re-enforcement of what I am indicating here.

--

Greetings,

Jerry Greenberg GLG Technologies GLG
=========================================
WebPage http://www.zoom-one.com
Electronics http://www.zoom-one.com/electron.htm
=========================================


Thanks for the info guys, spending time going over the schematic I
managed to work out what most of the trans were doing and had come to
a similar conclusion !

OK then, does anyone have an idea what the problem would be from the
symptoms -

The monitor powers up fine, but as soon as a video signal is
introduced it goes into standy mode ( flashing power light ) ???

Mike