Hello all ElectronicNoobBlog viewers,
Few day’s ago i got a 9V 7A very old (198x) years switching PSU.
It was “thrown away” because it was blowing fuse inside PSU and in power installation – so short was very massive:).
First after opening i spot swollen filter capacitor at 220V side.
I removed that filter cap (both) and replace with new one, then put new fuse in PSU and connect into power…
Bam! blown… fuses in lab goes off.
Fuse was very dark, so it’s mean massive short and lot’s of current passing.
To confirm, i soldered in place of FUSE 120W lamp and try again. Lamp was glow at full brightness with little flickering.
I started from checking rectifier diodes, and found one shorted.
I don’t have same type, so i replace all four with higher current and voltage.
It was little tight but still looks pretty.
Power again, lamp glow very very little in 1 second (when charging capacitors) and goes off.
After confirming output voltage i remove lamp, put fuse and put everything back for 24H test. – Work perfect!
Here are pictures from repair. You can spot “shorted” diode on meter (i measure working for contrast).
