Quote:
Originally Posted by Bullabill
Does anyone know where I might buy a suitable replacement power supply?
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I did not see one or even the part number for the whole power supply. Power circuit board assembly VEP01558C? I didnt see one on ebay or the web either but somewhere there is one or both. Its a nice idea.
Quote:
Originally Posted by Bullabill
when I check the voltage at pin 1 of IC1 I can't get a reading anything like the 58.0 on the power supply schematic. Using the ac. scale between the pin and the low side of the bridge gives me 256 volts which is about half of the p-p figure of the 'scope notation. No matter what combination of meter settings ac, dc, and probe positions I can't see anything close to the 58.0 figure.
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ground point.JPG
The schematic specifies where to place the ground probe when looking for the 58 volts on pin 1( I think that should be 58 volts dc measured with a volt meter)Its kind of fuzzy but looks like you want to put ground reference on pin 3 of IC 1
The waveform is shown there at pin 1 as a 520 volt peak to peak squarewave and although it does not specify frequency it shows a picture of an oscilliscope display at 5 micro seconds per division so if the waveform made a complete cycle in one division the frequency would be 1 divided by .000005 or 200 khz. If in two divisions 100 khz. Schematic does not specify but for the sake of argument say the frequency is something around 40 to 200 khz.
The ac input side of the schematic goes to a full wave bridge rectifier but the low side of the bridge is never refrenced to ground (hence the use of the opto isolater) it is just chopped up ac going into the transformer (at a rate of 100 or so kilohertz). I think this is called PWM pulse width modulation.
Theoretically (not that I recommend it without factory instructions) you could isolate all the switching regulator stuff on the left side of the page and drive the power transformet with line ac through a variac and get some activity on the output of the power supply (RCA televisions used to have a factory taught method for troublehsooting their chopper power supplies where you jumpered the primary winding on the flyback transformer and used a variac). That was 1980's technology we are looking at 2000's technology.
Would the output side of the power supply have any voltage at all if the oscillator/chopper was not working?
All outputs would be high or low or all have excell noise? What if the chopper was doing its job? Havent you already found confirmed failed componets on the output side of the transformer ?
I am interested in this circuit also due to similar design in my AG-1980 vcr(s) Please let me know if you learn anything about the cause.
