When you first attempt to turn this monitor on it does absolutlely nothing. I checked all the fuses and they are all 0.000 so i can rule that out. Next i checked the voltages at the plug coming off the power supply and i'm not getting +5v, i'm only getting .363v. The caps on the power supply are elite ED series. I checked evey capacitor on the power supply and i found 2 that were out of spec as per the datasheet. I did change the 2 with some used spares i have (lower esr). I'm getting 162v at the large cap.
Next i checked the PWM controller (LD7552BPS). I checked btween ground and vcc and i am not getting a shorted ohm reading. I plugged the power supply in and checked pins 3 & 7 (vcc) but my readings are in the 10v to 14v range and not stable.
I then checked the adjustable shunt regulator (AZ431AZ-EA1). Between the anonode and cathode i'm getting .571 & OL in the diode test mode on my multimeter. I plugged the power supply in and i'm getting .362v at the reference pin of the regulator.
I then checked the octocoupler (PC123). I'm sure if i'm doing this right but from the data sheet the one end has an anode and a cathode so in circuit it measures .571 & .795 so i removed it and it reads .997 & OL out if circuit. I think you need to do an led blink procedure to properly test these but i have never tried it. In circuit with the power supply plugged in i'm getting -55v on the primary side and .363v on the secondary side.
So i am unsure if the .363v readings i'm getting at the octocoupler and the shunt regulator would be my no 5v problem or the voltage fluctuations at the pwm controller. I did check the few diodes and resistors on the board and they check out ok. I also checked the Q901 power mosfet and it checks ok. And the 2 Schottky barrier rectifiers check good also.
So at this point i'm somewhat stumped. Sorry for the novel
Next i checked the PWM controller (LD7552BPS). I checked btween ground and vcc and i am not getting a shorted ohm reading. I plugged the power supply in and checked pins 3 & 7 (vcc) but my readings are in the 10v to 14v range and not stable.
I then checked the adjustable shunt regulator (AZ431AZ-EA1). Between the anonode and cathode i'm getting .571 & OL in the diode test mode on my multimeter. I plugged the power supply in and i'm getting .362v at the reference pin of the regulator.
I then checked the octocoupler (PC123). I'm sure if i'm doing this right but from the data sheet the one end has an anode and a cathode so in circuit it measures .571 & .795 so i removed it and it reads .997 & OL out if circuit. I think you need to do an led blink procedure to properly test these but i have never tried it. In circuit with the power supply plugged in i'm getting -55v on the primary side and .363v on the secondary side.
So i am unsure if the .363v readings i'm getting at the octocoupler and the shunt regulator would be my no 5v problem or the voltage fluctuations at the pwm controller. I did check the few diodes and resistors on the board and they check out ok. I also checked the Q901 power mosfet and it checks ok. And the 2 Schottky barrier rectifiers check good also.
So at this point i'm somewhat stumped. Sorry for the novel
Comment