1000+ Volts at B+

[onyxx]

Hello, i am working on a 15 inch color monitor. I have a 150W light
bulb connected and when i turn the monitor on, it starts to pulsate for
about 10 seconds at 2hz(+-)So it pulsates like 15 to 20 times and then
it stays at normal brightness. During all of this the monitor is NOT
connected to a PC, but when i do it statrs to pusate again but this
time indefenetly. I´ve tried changing the refresh rate and this causes
the pulses to speed up, so if i go from 800x600/50hz to 800x600/60hz,
the pulsating goes from about 1hz to 2hz and if I pull the VGA
connector the pulsating stops. Should i try a bigger light bulb?
I also get over 1000Vdc (DMM goes blank)both at the chopper
transistor´s and HOT´s drain pin. What controls B+ voltage? is it
just the HOT or is there a voltage regulator somewhere?
I am looking for a bad V regulatro or maybe a bad resistor somewhere,
Am I in the right direction here?
Thanks.

 

[Sam Goldwasser]

Hello, i am working on a 15 inch color monitor. I have a 150W light
bulb connected and when i turn the monitor on, it starts to pulsate for
about 10 seconds at 2hz(+-)So it pulsates like 15 to 20 times and then
it stays at normal brightness. During all of this the monitor is NOT
connected to a PC, but when i do it statrs to pusate again but this
time indefenetly. I´ve tried changing the refresh rate and this causes
the pulses to speed up, so if i go from 800x600/50hz to 800x600/60hz,
the pulsating goes from about 1hz to 2hz and if I pull the VGA
connector the pulsating stops. Should i try a bigger light bulb?
I also get over 1000Vdc (DMM goes blank)both at the chopper
transistor´s and HOT´s drain pin. What controls B+ voltage? is it
just the HOT or is there a voltage regulator somewhere?
I am looking for a bad V regulatro or maybe a bad resistor somewhere,
Am I in the right direction here?

What were the original symptoms?

100 W may be a bit low for a 15 inch monitor to come up properly with a
signal.

P.S. Don't put your poor DMM on those terminals! If it does come up
properly, the DMM may not survive.

--- sam | Sci.Electronics.Repair FAQ: http://www.repairfaq.org/
Repair | Main Table of Contents: http://www.repairfaq.org/REPAIR/
+Lasers | Sam's Laser FAQ: http://www.repairfaq.org/sam/lasersam.htm
| Mirror Sites: http://www.repairfaq.org/REPAIR/F_mirror.html

Important: Anything sent to the email address in the message header above is
ignored unless my full name is included in the subject line. Or, you can
contact me via the Feedback Form in the FAQs.

 

[crazy frog]

check the H-OUT transistor and any
caps in the power supply near hot spots
that may dry out the caps, disconnect the
h-out transistor before useing youre metre
to check the power supply, then use a light
bolb and connect it to ground and the collector
side of the h-out transistor on the board
with no transistor connected
it should be 120-150volts.

Hello, i am working on a 15 inch color monitor. I have a 150W light
bulb connected and when i turn the monitor on, it starts to pulsate for
about 10 seconds at 2hz(+-)So it pulsates like 15 to 20 times and then
it stays at normal brightness. During all of this the monitor is NOT
connected to a PC, but when i do it statrs to pusate again but this
time indefenetly. I´ve tried changing the refresh rate and this causes
the pulses to speed up, so if i go from 800x600/50hz to 800x600/60hz,
the pulsating goes from about 1hz to 2hz and if I pull the VGA
connector the pulsating stops. Should i try a bigger light bulb?
I also get over 1000Vdc (DMM goes blank)both at the chopper
transistor´s and HOT´s drain pin. What controls B+ voltage? is it
just the HOT or is there a voltage regulator somewhere?
I am looking for a bad V regulatro or maybe a bad resistor somewhere,
Am I in the right direction here?
Thanks.

 

[Andy]

Hi
are you using a scope, Digital or Analogue Meter?. There can be a difference
due to the waveform. I am not sure what to expect at flyback frequencies. I
am only happy when I get the same voltages as on the circuit diagram
(schematic)
Andy

Hello, i am working on a 15 inch color monitor. I have a 150W light
bulb connected and when i turn the monitor on, it starts to pulsate for
about 10 seconds at 2hz(+-)So it pulsates like 15 to 20 times and then
it stays at normal brightness. During all of this the monitor is NOT
connected to a PC, but when i do it statrs to pusate again but this
time indefenetly. I´ve tried changing the refresh rate and this causes
the pulses to speed up, so if i go from 800x600/50hz to 800x600/60hz,
the pulsating goes from about 1hz to 2hz and if I pull the VGA
connector the pulsating stops. Should i try a bigger light bulb?
I also get over 1000Vdc (DMM goes blank)both at the chopper
transistor´s and HOT´s drain pin. What controls B+ voltage? is it
just the HOT or is there a voltage regulator somewhere?
I am looking for a bad V regulatro or maybe a bad resistor somewhere,
Am I in the right direction here?
Thanks.

 

[Tom MacIntyre]

Hello, i am working on a 15 inch color monitor. I have a 150W light
bulb connected and when i turn the monitor on, it starts to pulsate for
about 10 seconds at 2hz(+-)So it pulsates like 15 to 20 times and then
it stays at normal brightness.

If it is at normal brightness...

During all of this the monitor is NOT
connected to a PC, but when i do it statrs to pusate again but this
time indefenetly. I´ve tried changing the refresh rate and this causes
the pulses to speed up, so if i go from 800x600/50hz to 800x600/60hz,
the pulsating goes from about 1hz to 2hz and if I pull the VGA
connector the pulsating stops. Should i try a bigger light bulb?
I also get over 1000Vdc (DMM goes blank)both at the chopper
transistor´s and HOT´s drain pin.

....it is no wonder that the DMM is complaining...if only I could
remember what "drain" means...FET terminal...equivalent to collector
or emmiter? Can't remember...if emitter, something weird is going on.
Hmmm.

Tom