PS503/Repairs: Difference between revisions

Revision as of 14:11, 23 February 2024

Tektronix PS503A Power Supply Restoration by NFM @ YouTube

PS503A Manual

There are errors in the circuit drawing:

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.
R48 is missing on the grid location table. It is in F1.
Other parts are missing on the grid location table (Q25, ...)

PS503A: Instable Output/Output voltage is decreasing with time

Problem: The output is instable (±100 mV) and is decreasing with time. 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).

C34 is shorted by the output-on button. So, replacing C34 with a tantalum capacitor is not recommended.

PS503A: Replacing the voltage indicator light bulb with a LED

to preserve the effect that the indicator lights up with higher output voltage, some resistor have to be changed.

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)
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)
The LED should be pushed as deep as possible into the bulb holder, so it holds the yellow plastic window part in place.
Choose R48/R148 and R55/R155 according the chosen LED (LED current and power dissipation of the resistor)
R48 is missing on the grid location table. It is in F1.

Pictures

DC current thru C34 (12 V / 10 mA limit)

@@ Line 3: / Line 3: @@
 ==PS503A Manual==
-There is an error in the circuit drawing: 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.
+There are errors in the circuit drawing:
+* 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.
+* R48 is missing on the grid location table. It is in F1.
+* Other parts are missing on the grid location table (Q25, ...)
 ==PS503A: Instable Output/Output voltage is decreasing with time==
-The output is instable (±100 mV) and is decreasing with time.
+Problem: The output is instable (±100 mV) and is decreasing with time.
-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).
+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).
 C34 is shorted by the output-on button. So, replacing C34 with a tantalum capacitor is not recommended.
+==PS503A: Replacing the voltage indicator light bulb with a LED==
+to preserve the effect that the indicator lights up with higher output voltage, some resistor have to be changed.
+* 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)
+* 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)
+* The LED should be pushed as deep as possible into the bulb holder, so it holds the yellow plastic window part in place.
+* Choose R48/R148 and R55/R155 according the chosen LED (LED current and power dissipation of the resistor)
+* R48 is missing on the grid location table. It is in F1.