Re: Fortron FSP300-60ATV repair
Back to the Power Q/Fortron power supply. After recapping, time to apply power and see what the 5vsb is doing. Nothing. Since it is a two transistor circuit and been through high temperature, I decided to simply gut the two transistor circuit and install a DM311 pwm chip. Put my LED tester on the main power supply connector and applied power. 5vsb LED came on.....success! So I grabbed my voltmeter to check the 5vsb voltage, and was surprised to find that it measured 17 volts. Yes, 17 volts.....a "regulated" 17 volts. Looks like the protection provided by the DM311 is overcurrent or overpower protection, NOT overvoltage protection. This is the first time I have ever seen a DM311 circuit go overvoltage.
The two key components to set the voltage level are the 431 regulator chip and the optoisolator chip. I decided to change the optoisolator chip first. Using a pullout optoisolator from another power supply, I installed it and applied power. Now it measures 5.2 volts. Now I am confident the 5vsb is fixed, no critical capacitor to worry about, and it will probably run for a long time. Now that the 5vsb is fixed, I can move on to troubleshoot the rest of the power supply.
Back to the Power Q/Fortron power supply. After recapping, time to apply power and see what the 5vsb is doing. Nothing. Since it is a two transistor circuit and been through high temperature, I decided to simply gut the two transistor circuit and install a DM311 pwm chip. Put my LED tester on the main power supply connector and applied power. 5vsb LED came on.....success! So I grabbed my voltmeter to check the 5vsb voltage, and was surprised to find that it measured 17 volts. Yes, 17 volts.....a "regulated" 17 volts. Looks like the protection provided by the DM311 is overcurrent or overpower protection, NOT overvoltage protection. This is the first time I have ever seen a DM311 circuit go overvoltage.
The two key components to set the voltage level are the 431 regulator chip and the optoisolator chip. I decided to change the optoisolator chip first. Using a pullout optoisolator from another power supply, I installed it and applied power. Now it measures 5.2 volts. Now I am confident the 5vsb is fixed, no critical capacitor to worry about, and it will probably run for a long time. Now that the 5vsb is fixed, I can move on to troubleshoot the rest of the power supply.
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