The Shenzhen Mastech HY3003-3 DC power supply is a linear triple output power supply with two adjustable 30V/3A outputs and one fixed 5V/3A output. It has an LED panel meter for each supply for voltage and current readout. Not surprising the calibration wasn’t perfect. So In an unrelated attempt to repair the 5V banana jacks, I decided to figure out how to calibrate it. It turns out it’s not too difficult.
WARNING – PROCEED AT YOUR OWN RISK. I am in no way liable for you hurting yourself or damaging your equipment.
Here is the procedure:
1) Remove the six sheet metal cover screws, three from each side and remove the top cover.
2) Power on the power supply and give it a few minutes to stabilize (thermally).
3) The LED seven segment displays are mounted on a green FR4 PCB with two WS7107CPL DMM chips – one for each supply.
4) Locate trimmer W1, it is located immediately adjacent to the WS7107. Using a millivolt DMM, set the voltage across pin 36 with respect to pin 35 to 100mV. Mine was 105mV prior to adjustment.
5) Set the power supply to maximum voltage – around 34V and plug a DMM into the output banana jacks. Now, locate trimmer W2 and adjust it so the panel meter agrees with the DMM.
6) Repeat for the second power supply and your done!