A question about this dvd power supply

[marco antonio]

In the connector CN3 I have 5 points where the voltage at 2 and 3 are erronus so according to the schematic could you tell me what could be the voltages at these two terminals. Q4 is a negative voltage regulator -24v. As you can see the voltage
at D4 is low due the winding has low turns. I was forgotten the voltage at 2 and 3 are -18.2 and -17.3 volts measured with the DMM.
rgds
marco

 

[betwixt]

The voltages are probably correct. Pins 2 & 3 are the filament supply to the fluorescent display and are not referenced to ground, they are referenced to pin 1 which is most likely the main supply line to the display.

To get a more accurate result you need to ensure there is some load on these supplies. The best test would be to look at the display in a dark room. If the voltages are correct you should see a dim glow from the filament wires. These are the thin wires that stretch from end to end of the display just inside the front glass. Usually there are two or three of them but sometimes more.

Brian.

 

[marco antonio]

Thanks for your response however when i checked the printer board where the conector is I read 3.3 v for pins 2 and 3 and the DMM is -18v and -17 vaprox. So i also understand them could be the voltages for the display filaments F an -F but the voltages are too high and analizying the circuit I can see how to get this 3.3 voltages.
That is my doubt.
rgds
marco

 

[betwixt]

3.3V is about right for the filament voltage but it has to be measured across pins 2 and 3, not to ground and you should measure it with the display connected.

In this kind of display, the filament is also the cathode connection, they work like vacuum tube triodes where the anode has to be more positive than the cathode for conduction to take place. In this case, the anode is probably ground and the cathode is made negative instead.

If those voltages are there, your problem is elsewhere in the unit. It seems the power supply is working OK.

Brian.