Electronics > Repair
Fixing Rohde & Schwarz FSIG (FSEA, FSIQ...) Ascom power supply
dl7oab:
Hello all.
I repaired this type of PS of my ZVC 5 years ago.
Back then, I replaced two leaky electrolytic capacitors and cleaned the pcb.
Unfortunately I didn't replace all of them.
Now it starts to fail again sometimes and I want to replace all electrolytic capacitors.
As so often it seems that they are a also weak point in this PS.
Does anybody have a list of electrolytic capacitors with capacity and voltage values, so that I can buy them before take my ZVC out of service and disassembling the PS?
Regards Matthias
Seiji53:
Hello. - Hello.
Attached is a picture of the electrolytic condenser information mounted on the power supply board.
There are two types of power supply boards. One with an electrolytic condenser of 10uF/50V and the other with 47uF/50V. (The part described on line 2)
We recommend replacing all electrolytic condensers on this board except the 470uF/630V. The total number of capacitors is 40.
The defective LM358 is caused by a leaking electrolytic capacitor (220uF/25V) attached to the sub-board above it. Therefore, if the LM358 is defective, the surrounding components should also be checked and replaced.
There was a mistake in the text, and the following is the corrected content.
condenser => Capacitor
47uF/50V=>47uF/63V
Andi555:
Hello,
I try to repair this PSU as well. I got a signal analyser with completly dead PSU without any blown mains fuse at the socket.
After disassembly there was only one visual dead capacitor on the PFC side. After removing it the Short disapeared.
Without the SMD capacitor the big mains capacitor mounted sideways only charges up to about 19V at regular line voltage -> nothing happens, -> only very small mains current consumption
When I charge the capacitor with an external DC PSU up to 70V the 12V standby voltage comes alive.
It seems to me that the PFC circuit responsible for charging the main filter cap is dead.
What do you guys suggest to continue measuring. I am a bit lost without a schematic and layout.
Shouldn't the main filter cap always charge to line voltage even the PFC is off? The PFC charges the capacitor only higher?
I realy appreciate any help, thank you in advance
Harry_22:
Hi Andi555!
Next week I will find broken PS and have a look for PFC.
ML4821 is responsible for PFC work.
Please find in attachment the connection diagram for PS standalone test.
73
Harry
Harry_22:
--- Quote from: Andi555 on September 06, 2024, 06:01:00 pm ---Hello,
Without the SMD capacitor the big mains capacitor mounted sideways only charges up to about 19V at regular line voltage -> nothing happens, -> only very small mains current consumption
--- End quote ---
Hi!
Even with inactive PFC, the voltage across the output capacitor should be up to peak rectified voltage. But you have significantly less.
Let's look at the example diagram from datasheet to see what could cause this.
ML4821 operates with the current sence resistor. Most likely it overheated and burned out as a result of SMD capacitor short.
Could you find it on PCB and check.
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