Manual do usuário TELEFUNKEN DPF 7321

[. . . ] ATX power supplies are available from virtually every computer shop. When you buy a new power supply it is obviously safe to assume it will be in perfect working order. But when you buy a (used) power supply at a computer fair or boot fair you want to be sure that it works before you fit it into the case and connect it to the motherboard. The true hobbyists may also want to investigate the exact fault in a broken power supply. [. . . ] The power supply is turned on by closing switch S2. This pulls pin PS_ON sufficiently low via R56. According to the specification this pin should be <0. 8 V at 1. 6 mA. The PWR_ON output, also called PWR_GOOD or PWR_OK, is used by the power supply to show that the most important outputs (+12 V, +5 V and +3. 3 V) are within their limits and can supply a nominal current. When this signal is active, D2 lights up. Since this output can only source 200 µA at a minimum voltage of 2. 4 V, a buffer stage consisting of R11, R12 and T1 has been added. Once the mains is turned on (and D1 and D2 are lit), S1 is used to select the voltage that is connected to the input of amplifier IC1b. S1 is a 2-pole 6-way rotary switch (it has to be a break-before-make type, otherwise you'll introduce shorts in the outputs). The first switch selects the supply voltage to be tested. The common output of this switch is also connected to a PCB pin (via a 100 resistor for protection). It is possible to connect a small voltmeter module to this pin, so that the absolute value of the selected voltage can be seen. This determines the tolerance ranges with respect to the 2. 5 V reference voltage. P1 is used to set the reference levels as accurately as possible. This just leaves the section that joins the output signal from IC1b to the LEDs. This output signal is nominally 2. 5 V and may be a bit more or less when it deviates. But the comparator circuit built round IC3b-d can only indicate negative differences. To get round this problem IC1a inverts the output signal from IC1b. This is followed by an analogue switch that can be controlled using a digital signal. This switch is part of IC2 (a triple analogue multiplexer). The output signal from IC1b and the inverted one from IC1a are connected to inputs Y0 and Y1 of an analogue switch (pins 2 and 1 on IC2). The output of IC1a is also connected to opamp IC3a, which acts as a comparator and compares the signal with the 2. 5 V reference voltage. The output of IC3a acts as the control signal for the analogue switch. [. . . ] Then connect the multimeter between R48 (from the lead nearest the mounting hole) and ground. The voltage at that point should then be adjusted with P1 to give a reading of 2. 00 V. The use of the tester is very straightforward. First connect the supply connector (either the 20-pin or the newer 24-pin) from the ATX power supply under test. [. . . ]