Hello,

I have read the FAQ for the newsgroup, but I'm pretty new when it comes to
monitor repairs.

I have a 21" Viewsonic P815 that won't display any picture at all. When
you plug the unit in and power it up the front LED light indicates power,
and also switches from green to orange if there is no video signal
attached. The very back of the neck glows, and after about 10 seconds or
so the monitor emits a high-pitched whine/pop for just a brief second
which causes the other monitor in the area to wobble a bit (is this the
auto-degauss kicking in?). Screen is always completely off (no static).

My research online seems to suggest that I should be checking the
horizontal output transistor first, but I'm unsure of what it looks like
or where I should connect my probes. Any books you'd recommend on
where to learn this stuff?

I'm not really vested in this monitor, but I picked it up for free and
figured there may be something relatively inexpensive and easy for me to
fix with my basic grasp of electronics. Anybody that can offer me some
tips or diagrams on how to proceed would be great. I checked the fuse on
the mainboard for continuity already, so that wasn't it.

Thanks,
Shaun

Without the proper technical training, supervised monitor service practice,
and service manuals, this would be very difficult to service. By the sounds
of your question, you should get some supervision. These monitors can be
very dangerous (safety hazard) to mess in. The power drive to the horiz
output is very high in current and the voltages under operation are also
very high.

The HV generator, sometimes referred to as the horiz output transistor is on
a heat sync near to the flyback transformer. If it is blown, then most
likely there are other parts that have also failed. Upon replacement, the
cause of failure must also be serviced.

Also, the scan amplifier sections can be at fault, including the power
supply itself. The tech would start by verifying the power supply
performance first, before directly getting in to the horiz output stage.

--

Greetings,

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


"Shaun Guth" wrote in message
news Hello,

I have read the FAQ for the newsgroup, but I'm pretty new when it comes to
monitor repairs.

I have a 21" Viewsonic P815 that won't display any picture at all. When
you plug the unit in and power it up the front LED light indicates power,
and also switches from green to orange if there is no video signal
attached. The very back of the neck glows, and after about 10 seconds or
so the monitor emits a high-pitched whine/pop for just a brief second
which causes the other monitor in the area to wobble a bit (is this the
auto-degauss kicking in?). Screen is always completely off (no static).

My research online seems to suggest that I should be checking the
horizontal output transistor first, but I'm unsure of what it looks like
or where I should connect my probes. Any books you'd recommend on
where to learn this stuff?

I'm not really vested in this monitor, but I picked it up for free and
figured there may be something relatively inexpensive and easy for me to
fix with my basic grasp of electronics. Anybody that can offer me some
tips or diagrams on how to proceed would be great. I checked the fuse on
the mainboard for continuity already, so that wasn't it.

Thanks,
Shaun

"Shaun Guth" wrote in message news
My research online seems to suggest that I should be checking the
horizontal output transistor first, but I'm unsure of what it looks like
or where I should connect my probes.

I have just completed a repair of 19" PS790 with similar symptoms
and I have fixed it with replacing this transistor with $6 NTE2958
bought at www.mouser.com - it is working as it was before...

Transistor will be located near the high voltage transformer area...
On a radiator, probably together with some diodes...
Both transistor and diodes will be in the TO220 case - transisor
will be in the isolated TO220 (without metal back plate).
This is power MOSFET transistor so expect it to behave like
mosfet when checking it... Mine had shorted channel.

In my case it was required to adjust tube voltages on the back
of the high-voltage transformer - needed to fixed focus...

Also, because of the shorted transistor, there was one burned
resistor in the +79V branch filter. It was serial with a small coil
and the electrolitic capacitor (the one for 100V). I just replaced
it with a small short, since I do not have the correct sub-ohm value.
I do not see anything wrong on the picture coming from this change.

Of course, your monitor will be a little different, so you have to
work with it on your own to find out...

On Wed, 31 Mar 2004 11:36:49 -0500, Jerry G. wrote:
The HV generator, sometimes referred to as the horiz output transistor is on
a heat sync near to the flyback transformer. If it is blown, then most
likely there are other parts that have also failed. Upon replacement, the
cause of failure must also be serviced.

Also, the scan amplifier sections can be at fault, including the power
supply itself. The tech would start by verifying the power supply
performance first, before directly getting in to the horiz output stage.

Thanks to both of you for your help, I guess I'll just dump the monitor
off on someone else for the time being. Getting in way over my head by
the sounds of things

Shaun