1000+ Volts at B+

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=B4ve 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=B4s and HOT=B4s 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.

Reply to
Loading thread data ...

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:

formatting link
Repair | Main Table of Contents:
formatting link

+Lasers | Sam's Laser FAQ:
formatting link
| Mirror Sites:
formatting link

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.

Reply to
Sam Goldwasser

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.

Reply to
crazy frog

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

Reply to

If it is at normal brightness...

...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.


Reply to
Tom MacIntyre

ElectronDepot website is not affiliated with any of the manufacturers or service providers discussed here. All logos and trade names are the property of their respective owners.