What does +3v3a mean in a schematic

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I dont quite understand.
The 1/2 wave looks like its top has been cut but has a "wave", the full wave part is much better ?
Cool.
Srinath.

There is no such thing here as one being "better" or worse than the other.

The "half wave" was not designed to be a power supply, but a power failure sensing circuit instead. It sends a train of 60Hz pulses to the micro controller on the front board so that as soon as there is one pulse missing the micro knows there is power interruption. This train of pulses has to be clipped by the zener D458 so that it swings between 0V and 5.1V in order to provide with a clearly defined logic "0" and "1" yet without exceeding the maximum amplitude allowed at the micro controller's I/O port.

From the simulations we could see this sensing circuit operates well with a wide range of transformer voltages, from 10.4V rms to 27Vrms.
 
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Hi,
Nattawa looking at your simulation means that they are looking at the zero crossing of the AC to turn On the amplifier to preventing the inrush current at power ON. As soon they see the pulse then they turn ON the amplifier. You will have a pulse when the AC it is positive and also when it is negative since they are taking the signal from the bridge.
 
Hi,
Nattawa looking at your simulation means that they are looking at the zero crossing of the AC to turn On the amplifier to preventing the inrush current at power ON. As soon they see the pulse then they turn ON the amplifier. You will have a pulse when the AC it is positive and also when it is negative since they are taking the signal from the bridge.

Unfortunately, Tauro0221, you took it the wrong way, I'm afraid. In a bridge rectifier circuit the transformer winding has a DC offset equivalent to 1/2 of the bridge output. When you take the negative output of the bridge as the reference potential, or the ground as does in the power board circuit, neither of the transformer winding terminals will ever go below the ground potential, i.e, they never go negative. It is one of the transformer winding terminals, not the bridge output, that the power failure sensing circuit takes signal from. Therefore, zero crossing is out of context here.

I don't know what made you believe any part of the circuit has anything to do with AC zero crossing, as nowhere in the power board design does anything has to do with AC zero crossing. This power board was designed having no zero crossing in mind, which is unnecessary any ways. The inrush current control is implemented by a power resistor R452 10-ohm/30W, and its bypass relay RLY452 is controlled by a simple R-C delay with no reference to mains AC timing.
 
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Hi,
Never mind that was an idea on what they are trying to accomplished by looking at your simulation of the circuit. The most important thing that we need it is a solid +12 volts at the output of the bridge so that when the micro see a positive voltage at the connector pin 2 in return it will turn on positive the base of of Q456 to enable the relays.
 
Relays turning on

There is no such thing here as one being "better" or worse than the other.

The "half wave" was not designed to be a power supply, but a power failure sensing circuit instead. It sends a train of 60Hz pulses to the micro controller on the front board so that as soon as there is one pulse missing the micro knows there is power interruption. This train of pulses has to be clipped by the zener D458 so that it swings between 0V and 5.1V in order to provide with a clearly defined logic "0" and "1" yet without exceeding the maximum amplitude allowed at the micro controller's I/O port.

From the simulations we could see this sensing circuit operates well with a wide range of transformer voltages, from 10.4V rms to 27Vrms.

So these pulses tell the micro chip in the display board that power is not interrupted.
The microchip then sends what voltage to CP458 pin 1 -
Then the full wave rectified section of the T451 is sent to pin 4 of CP458. That is 6v dc - OK why did the 10.4 trafo not make the relays click. I will try it again. In fact I should read my post on that test again. I may have not connected it to the front board, and if I did - and still didn't get the relays clicking. That would mean I have a bad chip in that front board doesn't it. Time to check what is in that circuit then.

Thanks.
Srinath.
 
Hi,
That it is what suppose to happen. Another test that you can do it is remove connector cp458 and jump pin 4 and 1 it will pick the relays. If not you still have a problem on the PS board. By doing the test your are applying 5 volt directly to the base of the transistor. What you doing it is simulating the micro. Remember you must have a minimum of 12 volts DC to pick up the relays.
 
The junction of c466 and r455 has whatever is the DC output of the trafo T451.
That feeds the collectors of transistors - q456, 455 and diodes d465 and d466 and goes to CP457 which turns on the switched power outlets.
What would the effect be on that if I dont have the rated voltage there ?
Will that prevent those relays from clicking.
I am not exactly sure those relays are good, I've run into a few dead relays in a few amps. In fact just 1 has to be bad, the one that has to click first. I am thinking of a 9v battery test for those done outside the board of course.

Cool.
Srinath.
 
Hi,
You can check the board easily by removing the board from the chassis. Connect 120 volts to the AC connector CP454. Jump pins 1 and 2 to the connector CP456. Apply power and check to make sure you have 12 volts going to the relays. Jump pins 1 and 4 at connector CP458 and the two relays should pickup. Remember you must have 12 volts going to the relays.

Warning Bremen take all the precautions when do the test. You are working with HIGH VOLTAGE.
 
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