Repairing Fortron 400W active pfc

[denkomenko]

Gratz from Bulgaria, sorry for the lenguage errors.

When the PSU came to me it was with broken chip FSDM311, 2ohm smd resistor from the "+" on the 400V cap and broken TL431. I replace them and trough 100W lamp its works, the voltages was great. When i put it on my PC after 3 sec it blows Now the 2ohm resistor is demaged again and the zener diode to pin3 of the FSDM311. Can you help with the value of the zener and can someone explain me what happened and why

thanks

[everell]

Re: Repairing Fortron 400W active pfc

Sounds like this psu might be having problems other than the DM311 which is the 5 volt standby circuit. First, take a look at the two APFC FET transistors and the main switching transistor. Look for shorts or leaky transistors. I am suspecting that one of your AFPC transistors is giving trouble. Do you have a voltmeter with which to measure volts and resistance? Have you had much training in electronics?

If the transistors are good, the DM311 circuit is not that complicated and I will try to guide you through some troubleshooting.

[everell]

Re: Repairing Fortron 400W active pfc

I took apart my Sparkle (Fortron) FSP 400-60GLC and the pc board looks just like the one in your picture.The missing resistor R44 is 2 ohms. The zener Z42 is a protection zener for the feedback pin. This pin should never go above 5 volts, so a 5.1 volt zener, a 5.6 volt zener, or even a 6.2 volt zener should work. In this circuit I have used both 5.1 volt zener and 5.6 volt zener. Either worked fine for me. I even ran the circuit without the zener, and it will work.

To start properly, the R4A resistor (1 meg) must provide startup current to pin 5. Make sure this resistor is not open. Once it tries to start, the chip gets its power (Vcc) at pin 2. The filter capacitor C13 (22 uF/50 volts) might be causing some trouble. I would change it just to be on the safe side. Do a quick check on R42 (2 ohms), D41 D40, and Z4. These parts are all part of the Vcc circuit.

You drew high current through the DM311 which blew R44 (2 ohms), the DM311 chip, and the TL431 regulator. There is an optoisolator (M3) between the DM311 and the TL431 regulator. You may have had a high voltage short which blew out this optoisolator. I would change it. You can probably find another one on a junked out power supply, if available. Carefully measure R46, R49, R48, and R47 in the TL431 regulator circuit. One of these resistors may have changed value when the TL431 blew out.

And finally, the protection snubber, used to prevent reverse kickback voltage to the DM311 output might have a bad component, which is D42 (which might be shorted), R43 (1 meg which might be open), and C42.

Check all of these components, and we will be better able to decide what happened. One more thing, sometimes the transformer shorts. Measure resistance from DM311 pins 6, 7, and 8 (all 3 tied together) to the plus side of the main capacitor (you marked this point with a +). This should measure about 6 ohms. This measures R44 (2 ohms) in series with the transformer primary which should be about 4 ohms. If you only get about 2 ohms instead of 6 ohms, the transformer primary is shorted.

Let us know what you find so we will know how your project turned out.