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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
onyxx
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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.

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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
Andy

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.

Tom

Reply to
Tom MacIntyre

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