Resonant Switching Power Supply

meins_da

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Feb 23, 2019
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Hello,

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.


Peter



image_lplfxm.jpg
 
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:
http://www.ti.com/lit/ds/symlink/tl594.pdf
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.
 
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.
 
Partially agree, check the diode, but also dying capacitors may be a problem and cause high current drain.
 
Hello

so after some time, i have now time to must repair this power supply! Thanks to all users how help me!
Ok, now i will start with repairing.

At the Moment. The first time the powersupply starts and work correct, but if i power off and power on in About 1 Minute the power supply will tick...

@winny which Diode do you mean? All at the top of the Picture?

Should i Change all output capacitors?

Thanks

Peter


P.S.: I attached a Picture without cables at the Output.

image_dyvrqo.jpg

image_ztnppe.jpg
 
So today i have Change all caps at the Output - no difference.
I only find out, if the voltage on R2 or R2 is About 20V i can Restart the power supply without any Problems....
 
Update!
I want to test the System with a electronic load. With 12V you can start with 2A. Then i would test the -12V as next Output voltage, the load says always 0V. After a time of waiting switch the power supply on and i have -12V on the Pins. Now i must find out how they generate the -12V.
 
meins_da said:
Update!
I want to test the System with a electronic load. With 12V you can start with 2A. Then i would test the -12V as next Output voltage, the load says always 0V. After a time of waiting switch the power supply on and i have -12V on the Pins. Now i must find out how they generate the -12V.
here are the voltages

there is a crowbar on the 5v line... activates around 6v

image_zilsaq.jpg
 
Because it is working normally sometimes, it appears it is not a diode shorted.
OK, so the crowbar (over-voltage clamp) may be activating?

What load(s) are you connecting to it?
Are you loading all the rails?
If you start the unit with different loads, does it get the problem tic-tic?
eg, small load
medium load,
full load
You may need some load on each output voltage rail especially the main +5V rail.
 
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