BAM - BANG - BOOM!
Good Day to the gang,
it's not only the (in)famous RIFA filter caps that can cause us much grief - other RFI filters can emit that magic smoke, too :-(
Today, my GRUNDIG PN300 power supplies have
both decided to let me down. If you are not familair with this model: These are quite nice, linear, triple output power supplies from the 90s, when GRUNDIG's history as a manufacturer of T&M equipment was already on its way to its bitter end. They feature two independent outputs for up to 30V and 2.3A and one fixed 5V/2A output. They can also be used as a simple curvetracer as they feature a GPIB/serial interface. Based on a toroidal transformer, they are quite reliable.
Well, quite...I own two of these, both were maintained (minor repairs) and calibrated by myself.
The first unit had a stuck relay, so instead of 5V DC, it provided 25V DC for a brief moment.
Thankfully, I still had my index finger on the OUTPUT ON button and so I had managed to switched it off even before the current limiter cut it out.
Then the second unit came to replace it and after about 1.5 hrs of operation under very light load conditions, I heard the magic "ZZZZZZZZP - BANG!" noise we all love so much.
I have acted immediately, identified what equipment had failed and down to the basement with it. Turned out that the RFI-filter has decided to throw in the towel and it began to spit its guts out. I had a quick clean up with window cleaner and a brush, blew the excess off with pressurized air and gave it a good rinse with IPA/alcohol. Some kitchen paper soaked up the liquid and I have repeated this twice after I had removed the internal assembly that holds the on/off switch and the line voltage switch. I have just ordered a replacement RF-filter that shall arrive early next week. Until then, this bugger dries on the heating.
BUGGERS! Have a good weekend, all.
THDplusN_bad