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Resonant Switching Power Supply

I Need help to repair a Power Supply. It is a very old device but it works very good, better than a new one so thats why i want to repair it.
It is a Resonant Power Technology Inc. RPM-101/4. It seems the same power supply is the RPM-201/4 but this has a additional Output voltage but seems based on the same device.
Sometimes if i switch on the device it works without any Troubles and don't stop working while i am working with this device but most of the time if i switch on power (it has an old one on/off mechanical switch) it make "tak tak tak" with a repeat time About 1 sec.
I already have Change the main Elkos (the red one on the picture). if i messure ith my multimeter the voltage on the Elkos in normal mode i get 48V (bipolar, there is a Center connector on the Transformator). But if don't work i see the value an my multimeter but the it crash down.

i hope you can help me to find the failure.


The tak-tak-tak sound is this power supply trying to start but shutting down again - this is typically because something is drawing too much current.
Or the current overload sense part is being triggered.
Might be over shooting voltage on start-up (try replacing the other electro caps on right side)
Can you make some DC loads with eg 5W resistors & power on to test?

Another common issue in similar PSUs is the resistors R2 + R3 going higher resistance. Maybe measure these guys, should = 47k ohms (lift one end to test with power off >10mins).
Be careful as these two are across main input capacitors and may have a high voltage across them even after switch off.

You will probably need an oscilloscope to go further.
Look at the two chips on the bottom right side TL594, data sheet here:
Check what is happening on pin 3 of each chip. If one chip is pulsing like the tak-tak sound, then check the input pins 1 +16, trace that via parts & board tracks.

Be careful, don't get a shock! The left side is all live to mains and has about 340V DC stored.
Running off solar, DIY & electronics fan :-)
EE by trade here. I design these things for a living.

My guess would be output diode is shorted. Set your multimeter to diode mode and measure source-drain of every mosfet and anode-cathode of every diode and report back.
No. cells
Indexed: 53
Processed ok, not yet indexed: ~1500
Broken down, untested: ~800
Not yet broken down: ~140 kg
Partially agree, check the diode, but also dying capacitors may be a problem and cause high current drain.

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