Electronics > Repair
Fixing Rohde & Schwarz FSIG (FSEA, FSIQ...) Ascom power supply
Harry_22:
I found PS with a similar malfunction. SMD capacitor also burned out.
Unfortunately the customer tried to fix it himself but did it carelessly.
The circuit is a little more complicated (please see the picture). There is a soft start on the IGBT transistor. Check it and both MOSFETs.
Andi555:
Thank you very much,
I will test the boards with you info the upcoming days.
There is a IGBT / Mosfet ? beside the rectifier which switches the recified DC (Minus) filter cap to Ground (Rectifier) -> Maybe this is some kind of overvoltage protection ?
Harry_22:
Hi Andi555!
I added soft start resistor to the diagram above. In my PS it burned out and was replaced with 20 Ohms. Through this resistor a smooth charge of the 470uF capacitor is carried out. Then the transistor opens shunting the resistor.
Most likely this resistor burned out.
Check all the parts circled in red.
Andi555:
Thank you Harry for your detailed description!
One hint: The diode symbol right beside the 6,3A fuse is drawn in the oposite orientation. I checked all the marked parts and indeed the 20Ohm start resistor is burnt to "open". The soldering joint also looks like it heated up for a long time.
For the test setup I shorted the resistor and turned up my variac slowly .... -> The PSU now works! :clap:
The burned capacitor is still not in place, maybe it is not realy necessary. Do you know the value? Otherwise I will leave it open.
Jarek:
Hello
I soldered one like this.
https://pl.farnell.com/murata/grj55dr72j224kwj1l/cap-0-22-f-630v-10-x7r-2220/dp/2218826
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