My 4-year old 19" Dell (Sony) monitor is having some HV problems. Yesterday
my 12-year old daughter said it "popped" a couple times and the screen
flashed/changed size along with the pop and then returned to normal. She
came to get me immediately and when I got there it seemed to be fine for
about 5 minutes, then popped once and lost the image completely. I turned
off the monitor right away at the switch, waited a few minutes, then tried
to power it back up. It turned on, lost the picture within a fraction of a
second, and began emitting a new barely audible sound. This sounded to me
like a high voltage discharge so I disconnected the unit from the computer
and carried it down to my bench for further analysis.

I opened up the monitor case, removed the right (looking from the rear)
metal HV shield and then plugged in and turned on the monitor without a
video input signal under a low light situation to see if I could identify a
flash/spark that was accompanying the sound. This proved to be very easy
since it was a glass discharge protector located at designation SG901. (It
lit up pretty much like a neon bulb...) I kept it powered up just long
enough to verify that none of the other protectors on the CRT socket board
were lit and that the sound was coming from only the one device. I saw no
obvious arcing or shorts anywhere. My assumption here is that the HV output
has drifted high and the discharge is the protection which was designed to
kick in working as expected.

I have removed the main board, but do not have a schematic. I'd like to
start with the assumption that the protector is working as designed and
check the values of the critical components in this circuit against their
specified values. Unfortunately, I do not have a schematic to identify
which ones they would be. I'm hoping that someone can send me the schematic
and/or their recommendation on fixing the problem.

Prior to encountering this issue, the monitor had worked flawlessly and I
would prefer not to have to purchase a replacement. Thanks in advance for
your assistance and thoughts.

Bob

First try cleaning the spark gap..
Second disconnect the base assembly an see if it arcs whilst disconnected



"Bob Shuman" wrote in message
...
My 4-year old 19" Dell (Sony) monitor is having some HV problems.
Yesterday
my 12-year old daughter said it "popped" a couple times and the screen
flashed/changed size along with the pop and then returned to normal. She
came to get me immediately and when I got there it seemed to be fine for
about 5 minutes, then popped once and lost the image completely. I turned
off the monitor right away at the switch, waited a few minutes, then tried
to power it back up. It turned on, lost the picture within a fraction of
a
second, and began emitting a new barely audible sound. This sounded to me
like a high voltage discharge so I disconnected the unit from the computer
and carried it down to my bench for further analysis.

I opened up the monitor case, removed the right (looking from the rear)
metal HV shield and then plugged in and turned on the monitor without a
video input signal under a low light situation to see if I could identify
a
flash/spark that was accompanying the sound. This proved to be very easy
since it was a glass discharge protector located at designation SG901.
(It
lit up pretty much like a neon bulb...) I kept it powered up just long
enough to verify that none of the other protectors on the CRT socket board
were lit and that the sound was coming from only the one device. I saw no
obvious arcing or shorts anywhere. My assumption here is that the HV
output
has drifted high and the discharge is the protection which was designed to
kick in working as expected.

I have removed the main board, but do not have a schematic. I'd like to
start with the assumption that the protector is working as designed and
check the values of the critical components in this circuit against their
specified values. Unfortunately, I do not have a schematic to identify
which ones they would be. I'm hoping that someone can send me the
schematic
and/or their recommendation on fixing the problem.

Prior to encountering this issue, the monitor had worked flawlessly and I
would prefer not to have to purchase a replacement. Thanks in advance for
your assistance and thoughts.

Bob

Kip,

Thanks for the reply. The device that is sparking is a sealed glass bulb.
It most closely resembles a neon bulb. It has two soldered in leads and the
"spark gap" appears to be inside a gas filled glass cavity. My guess here
is that the electrode distance is fixed and that the distance coupled with
the type of gas inside the bulb probably determines the breakdown voltage.

As such there is no way to clean the spark gap as you have recommended. I
could certainly remove the device and see what happens, or find a
replacement. I may even be able to swap it with one of the other devices on
the CRT socket board which appear to be the same. I am leery of doing this
though right away. I would prefer to test the critical devices first to see
is any has drifted out of spec over time. I also would appreciate getting
the schematic so that I can confirm the other devices are in fact the same
value so could be swapped.

Thanks again. Let me know if you have additional feedback or thoughts.
Sorry for not being more clear on the type of voltage surge device being
employed.

Bob

"kip" wrote in message
.. .
First try cleaning the spark gap..
Second disconnect the base assembly an see if it arcs whilst disconnected

Cleaning the spark gap isn't going to fix it.
Those monitors are notorious for failing focus dividers on the flyback
and capacitors going high esr in the power supply, both of which can
cause the focus voltage to go too high and the spark gap to arc over.

In addition the simple check is to make sure the ground pins on the
flyback are all good. Rarely on some monitors if the divider resistor
ground pin solder connection breaks loose the focus voltage also will
go way high.

Thanks. I have visually inspected all the flyback pins and the solder does
look good. I can retouch all of them as this is fairly simple with the
board out. On the high ESR elecrolytics, which component numbers or do you
suggest I check them all? A quick visual inspection did not yield any that
appeared to be bulging and I did begin to test ESR on the largest PSU
section capacitors, but they checked out low in circuit with the Dick Smith
ESR meter.

What I really need is the schematic so I can see what would cause the
voltage to be high on that particular protection device. I could then
remove leads of suspected resistors, caps, and diodes to test them correctly
with my DMM and the ESR meter.

But, unfortunately without the schematic I can only hunt and peck based on
tracing the conductor paths and this is extremely difficult due to the
density and physical layout (there are several large heat sinks obstructing
view/access). This group has always come through for me in the past ... so
I remain optimistic that someone will be able to help me out.

Bob

wrote in message
ups.com...
Cleaning the spark gap isn't going to fix it.
Those monitors are notorious for failing focus dividers on the flyback
and capacitors going high esr in the power supply, both of which can
cause the focus voltage to go too high and the spark gap to arc over.

In addition the simple check is to make sure the ground pins on the
flyback are all good. Rarely on some monitors if the divider resistor
ground pin solder connection breaks loose the focus voltage also will
go way high.

Ok Fine the reason I suggested clean the gap was because
I just had one similar on an RCA TV that was in a sort of damp
location and cleaning did the trick.Best of luck trouble shooting
the Monitor .Most probably a bad IHVT or Focus Network if it has one.

kip


kip
"Bob Shuman" wrote in message
...
Kip,

Thanks for the reply. The device that is sparking is a sealed glass bulb.
It most closely resembles a neon bulb. It has two soldered in leads and
the
"spark gap" appears to be inside a gas filled glass cavity. My guess here
is that the electrode distance is fixed and that the distance coupled with
the type of gas inside the bulb probably determines the breakdown voltage.

As such there is no way to clean the spark gap as you have recommended. I
could certainly remove the device and see what happens, or find a
replacement. I may even be able to swap it with one of the other devices
on
the CRT socket board which appear to be the same. I am leery of doing
this
though right away. I would prefer to test the critical devices first to
see
is any has drifted out of spec over time. I also would appreciate getting
the schematic so that I can confirm the other devices are in fact the same
value so could be swapped.

Thanks again. Let me know if you have additional feedback or thoughts.
Sorry for not being more clear on the type of voltage surge device being
employed.

Bob

"kip" wrote in message
.. .
First try cleaning the spark gap..
Second disconnect the base assembly an see if it arcs whilst disconnected

Thanks again for the response. Just wish I had the schematic!

Bob

"kip" wrote in message
.. .
Ok Fine the reason I suggested clean the gap was because
I just had one similar on an RCA TV that was in a sort of damp
location and cleaning did the trick.Best of luck trouble shooting
the Monitor .Most probably a bad IHVT or Focus Network if it has one.

kip

You don't need a schematic to troubleshoot a bad focus resistor
divider.

This might be the info you want:
http://www.eserviceinfo.com/service_...ets_d_400.html

Hopefully will help with any other potential issues.
Be aware that if something happens to corrupt the eeprom that holds the
alignment data, you will have to send it off for repair as hte computer
interface and software to perform an alignment is not cost effective to
buy for only one monitor.

Thanks ... I found my monitor, the Dell P991, on the list and successfully
downloaded three .rar files. What application opens these? I thought they
would be .pdf and could be read with Adobe Acrobat, but I do not think I
have seen a .rar file before. If I can get these open then I can read what
is there and see if this is what I need.

Sorry to be such a pain... I do appreciate directing me here. This site did
not come up when I did a Google search. It appears to have a lot of info
and be from Bulgaria!

Bob

wrote in message
ups.com...
You don't need a schematic to troubleshoot a bad focus resistor
divider.

This might be the info you want:
http://www.eserviceinfo.com/service_...ets_d_400.html

Hopefully will help with any other potential issues.
Be aware that if something happens to corrupt the eeprom that holds the
alignment data, you will have to send it off for repair as hte computer
interface and software to perform an alignment is not cost effective to
buy for only one monitor.

Bob Shuman wrote:
Thanks ... I found my monitor, the Dell P991, on the list and successfully
downloaded three .rar files. What application opens these? I thought they
would be .pdf and could be read with Adobe Acrobat, but I do not think I
have seen a .rar file before. If I can get these open then I can read what
is there and see if this is what I need.

Sorry to be such a pain... I do appreciate directing me here. This site did
not come up when I did a Google search. It appears to have a lot of info
and be from Bulgaria!

Bob

wrote in message
ups.com...

You don't need a schematic to troubleshoot a bad focus resistor
divider.

This might be the info you want:
http://www.eserviceinfo.com/service_...ets_d_400.html

Hopefully will help with any other potential issues.
Be aware that if something happens to corrupt the eeprom that holds the
alignment data, you will have to send it off for repair as hte computer
interface and software to perform an alignment is not cost effective to
buy for only one monitor.




I just plonk rar files into winzip and that works
for me -)-)-)

You need winrar to open them..


"Bob Shuman" wrote in message
...
Thanks ... I found my monitor, the Dell P991, on the list and successfully
downloaded three .rar files. What application opens these? I thought
they
would be .pdf and could be read with Adobe Acrobat, but I do not think I
have seen a .rar file before. If I can get these open then I can read
what
is there and see if this is what I need.

Sorry to be such a pain... I do appreciate directing me here. This site
did
not come up when I did a Google search. It appears to have a lot of info
and be from Bulgaria!

Bob

wrote in message
ups.com...
You don't need a schematic to troubleshoot a bad focus resistor
divider.

This might be the info you want:
http://www.eserviceinfo.com/service_...ets_d_400.html

Hopefully will help with any other potential issues.
Be aware that if something happens to corrupt the eeprom that holds the
alignment data, you will have to send it off for repair as hte computer
interface and software to perform an alignment is not cost effective to
buy for only one monitor.

Thanks. I'll try Winzip first as was suggested, then see if I can find this
other app if needed.

Bob

"kip" wrote in message
.. .
You need winrar to open them..

Kip,

Thanks again. I downloaded winrar and also winDJview to open the .DJVU file
that was inside the .rar archive. This contained the full service manual
and a schematic as well so I think I am good for now.

It never ceases to amaze me how this group always comes through.

Bob