Make sure you get quality caps when you replace them.
BE CAREFUL. THERE IS A VERY LARGE ENERGY HAZARD IN THESE CHARGED CAPS SO BE SURE TO OBSERVE PROPER SAFETY PRECAUTIONS!
Here is what I recommend once you get your new caps to "form" them properly before installation.
1. Using your PL700 frame power supply (unless you have a 100V DC power supply, unlikely), run a ground jumper clip from the copper ground bus bar between the 2 bulk caps in your amp to the minus terminal of your new cap that you intend to install.
2. Next using a jumper with a 2K ohm 2W resistor in series connect one end to the plus rail inside the Phase Linear amp power supply. Attach the other end to the positive terminal of your new cap that you intend to install.
3. Hook your DMM across the 2K ohm resistor with the positive DMM lead at the power supply end of the resistor and the negative DMM lead on the end of the resistor that goes to the cap being formed.
4. Apply power to the Phase Linear power supply.
5. As the cap being formed charges up you will see the voltage across the 2K ohm resistor start at a very high voltage and then gradually decrease as the cap reaches full charge.
6. Allow it to "form" for a long time. I run the caps that I sell for the PL400 for 2 days prior to shipping.
7. Once your forming time is complete, measure the leakage current for the caps at voltage by dividing the voltage observed across the 2K ohm resistor by the resistance (2000) to get the leakage current in microamps. Accept caps that have less than 50 uA of leakage at rated voltage and reject those that do not. 50uA translates to 100 mV across the resistor. You should see the voltage plateau at this very low level and stay there for many hours and only fluctuate a few millivolts, this indicates that the forming process has worked. If you see the current bottom out and then start rising again, this is generally not a good sign and you should watch this carefully.
8. Before removing the caps from forming, be sure to discharge them first by turning off the PL frame and letting the cap bleed down through the 2K ohm resistor. This takes a long time. Measure and check for near zero voltage on the cap being formed before you disconnect the test leads.
9. MOST OF ALL, BE CAREFUL. THERE IS A VERY LARGE ENERGY HAZARD IN THESE CHARGED CAPS SO BE SURE TO OBSERVE PROPER SAFETY PRECAUTIONS!
10. If all these steps check out, repeat for the next cap.
11. Once done, install the caps.
Forming is a process of building up the aluminum oxide coating on the capacitor foil inside the capacitor "jelly roll". The oxide acts as an additional insulator against capacitor breakdown and leakage. It is an electrochemical process that takes place when you do this. Once done and put into service, the capacitor will settle in at the voltage that it typically sees in the final application and adjust its oxide layer to suit. Caps that have been in storage a long time, especially at elevated temperatures tend to lose some of this oxide coating on the foil and leak more. These caps may take a longer time to properly form. Most recover fine but some do not. Those that do not should not be used.
BE CAREFUL. THERE IS A VERY LARGE ENERGY HAZARD IN THESE CHARGED CAPS SO BE SURE TO OBSERVE PROPER SAFETY PRECAUTIONS!
Here is what I recommend once you get your new caps to "form" them properly before installation.
1. Using your PL700 frame power supply (unless you have a 100V DC power supply, unlikely), run a ground jumper clip from the copper ground bus bar between the 2 bulk caps in your amp to the minus terminal of your new cap that you intend to install.
2. Next using a jumper with a 2K ohm 2W resistor in series connect one end to the plus rail inside the Phase Linear amp power supply. Attach the other end to the positive terminal of your new cap that you intend to install.
3. Hook your DMM across the 2K ohm resistor with the positive DMM lead at the power supply end of the resistor and the negative DMM lead on the end of the resistor that goes to the cap being formed.
4. Apply power to the Phase Linear power supply.
5. As the cap being formed charges up you will see the voltage across the 2K ohm resistor start at a very high voltage and then gradually decrease as the cap reaches full charge.
6. Allow it to "form" for a long time. I run the caps that I sell for the PL400 for 2 days prior to shipping.
7. Once your forming time is complete, measure the leakage current for the caps at voltage by dividing the voltage observed across the 2K ohm resistor by the resistance (2000) to get the leakage current in microamps. Accept caps that have less than 50 uA of leakage at rated voltage and reject those that do not. 50uA translates to 100 mV across the resistor. You should see the voltage plateau at this very low level and stay there for many hours and only fluctuate a few millivolts, this indicates that the forming process has worked. If you see the current bottom out and then start rising again, this is generally not a good sign and you should watch this carefully.
8. Before removing the caps from forming, be sure to discharge them first by turning off the PL frame and letting the cap bleed down through the 2K ohm resistor. This takes a long time. Measure and check for near zero voltage on the cap being formed before you disconnect the test leads.
9. MOST OF ALL, BE CAREFUL. THERE IS A VERY LARGE ENERGY HAZARD IN THESE CHARGED CAPS SO BE SURE TO OBSERVE PROPER SAFETY PRECAUTIONS!
10. If all these steps check out, repeat for the next cap.
11. Once done, install the caps.
Forming is a process of building up the aluminum oxide coating on the capacitor foil inside the capacitor "jelly roll". The oxide acts as an additional insulator against capacitor breakdown and leakage. It is an electrochemical process that takes place when you do this. Once done and put into service, the capacitor will settle in at the voltage that it typically sees in the final application and adjust its oxide layer to suit. Caps that have been in storage a long time, especially at elevated temperatures tend to lose some of this oxide coating on the foil and leak more. These caps may take a longer time to properly form. Most recover fine but some do not. Those that do not should not be used.