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| * [https://www.youtube.com/watch?v=h5ZH7e3sXbo Tektronix PS503A Power Supply Restoration] by NFM @ YouTube | | * [https://www.youtube.com/watch?v=--AbTooK15s Tektronix PS503 and PS503A Dual Power Supply Repairs] by Bob Haas, VintageTEK Museum @ YouTube |
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| ==PS503A Manual==
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| There are errors in the circuit drawing:
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| * All amplifiers are connected to +5 V or -5 V. In fact they are connected to the +6.2 V or -6.2 V supply.
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| * R48 is missing on the grid location table. It is in F1.
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| * Other parts are missing on the grid location table (Q25, ...)
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| ==PS503A: Instable Output/Output voltage is decreasing with time==
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| Problem: The output is instable (±100 mV) and is decreasing with time.
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| Solution: The faulty part was C34 (4.7 µF/50 V). C34 stabilises the reference voltage. Measuring C34 with an RLC-meter shows no fault: 5.0 µF and a serial resistance of 5 Ω. The faulty behaviour of C34 can only be seen by applying a DC voltage (see picture).
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| C34 is shorted by the output-on button. So, replacing C34 with a tantalum capacitor is not recommended.
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| ==PS503A: Replacing the voltage indicator light bulb with a LED==
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| to preserve the effect that the indicator lights up with higher output voltage, some resistor have to be changed.
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| * R48 (+ output) and R148 (- output) limits the low current that will always flow when the output is ON. This current will flow at 0 V output voltage. (supplied by +33 V / -33 V)
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| * R55 (+ output) and R155 (- output) limits the high current that will be added to the low current according to the output voltage. (supplied by the 0 to 20 V output voltage)
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| * The LED should be pushed as deep as possible into the bulb holder, so it holds the yellow plastic window part in place.
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| * Choose R48/R148 and R55/R155 according the chosen LED (LED current and power dissipation of the resistor)
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| * R48 is missing on the grid location table. It is in F1.
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| ==Pictures==
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| <gallery>
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| PS503A - Current C34.png|DC current thru C34 (12 V / 10 mA limit)
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| </gallery>
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| [[Category:Instrument repair reports]] | | [[Category:Instrument repair reports]] |