Wtb: Tutor for Schematics

troxel

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Seriously, I need someone to hold my hand on a few examples so I can get a better understanding. I know most of the basic and just need help putting it all together. If you can help, shoot me a PM. I will compensate for time.
 
There are lots of websites out there that go over reading schematics in detail. First learn all the symbols and abbreviations and most of the rest will be obvious.
 
I know the symbols and abbreviations. Just not quite sure of the "flow". Do you have any good references?
 
My approach to "flow" is to start from whatever isn't working and just follow the wires until they get to components.

Check those components, move on.
 
Thanks for the help so far. Maybe an example will help me more. I am starting to understand basic logic gates, flip flops, mux, demux, decoders, etc. I think it's actually more the components that are throwing me off. At least with chips you know inputs and outputs and have a general idea of flow.

Let's say I am having problems with the +5 on this PS. Can someone mark on the schematic with arrows that direction of flow starting from the output?

I realize there are multiple paths, but this is where I get confused at. I started the path, but come to the first point (1), and not sure if it keeps going left or down. I traced the down path to the IC, and was thinking that was an output, but looking up the chip looks like its Noninverted input. So that means the +5 is coming from the left (across the coil and by c24, c25)?

Hope I can post the photo, if not I will delete it.
 
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The +5v is fed from the lower half of T3 in the diagram - the AC signal coming into T3 is stepped down and convertered to DC through the 2 diodes (rectifiers) FD1 (what the label looks like on the diagram).

IC1 - not sure what it is doing right now without a part number, but the 5v could be power for it - or it could be regulating the 5v
 
That helps some. Thanks LJ. The IC1 is KA7500B or TL494CN (NTE 1729). Any other thoughts? What's going on with the T1 part of the circuit?
 
That helps some. Thanks LJ. The IC1 is KA7500B or TL494CN (NTE 1729). Any other thoughts? What's going on with the T1 part of the circuit?

The T1 section in this case looks like it is only there to help with stabalization of the +5v using pulse width modulation control (IC1).

Ok, the long form of circuit operation (hope this helps and makes sense):

The power supply is essentially controlled by IC1. When power transistors Q1 and Q2 are closed, then Q3 and Q4 are opened. When we want to open one from power transistors (Q1, Q2), then we have to close his exciting transistor (Q3, Q4). Current goes via R17 and D5 and one winding T1. This current excite voltage on base of power transistor and due to positive feedback transistor goes quickly to saturation. When the impulse is finished, then both exciting transistors goes to open. Positive feedback dissapears and overshoot on the exciting winding quickly closes power transistor. After it is process repetead with second transistor. Transistors Q1 and Q2 alternately connects one end of primary winding to positive or negative voltage. Power branch goes from emitor of Q1 (collector Q2) through the second winding of exciting transformer T1. Next through capacitor C7 and primary winding of main transformer T3 to the virtual center of supply voltage.

Output voltage stabilisation is achived by feeding back the output voltage back to IC1 (pin 1). From the internal 5-V reference regulator (pin 14 IC1) goes reference voltage through the voltage divider R?/R21 to inverting input on IC1(pin 2). Feedback R20, C13 provides stability of the regulator. Voltage from error amplifier is compared to the ramp voltage across capacitor C11. When the output voltage is decreased, then voltage on the error amplifier is decreased also. Exciting pulse is longer, power transistors Q1 and Q2 are longer opened, width of pulse before output coil is grater and output power is increased. The second error amplifier is blocked by voltage on the pin 15 IC1.

[edit to add] T1 is there mainly for isolation between the low voltage and high voltage sides.
 
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